Magnetic microwires can present excellent soft magnetic properties and a giant magnetoimpedance e... more Magnetic microwires can present excellent soft magnetic properties and a giant magnetoimpedance effect. In this paper, we present our last results on the effect of postprocessing allowing optimization of the magnetoimpedance effect in Co-rich microwires suitable for magnetic microsensor applications. Giant magnetoimpedance effect improvement was achieved either by annealing or stress-annealing. Annealed Co-rich presents rectangular hysteresis loops. However, an improvement in magnetoimpedance ratio is observed at fairly high annealing temperatures over a wide frequency range. Application of stress during annealing at moderate values of annealing temperatures and stress allows for a remarkable decrease in coercivity and increase in squareness ratio and further giant magnetoimpedance effect improvement. Stress-annealing, carried out at sufficiently high temperatures and/or stress allowed induction of transverse magnetic anisotropy, as well as magnetoimpedance effect improvement. Enhanced magnetoimpedance ratio values for annealed and stress-annealed samples and frequency dependence of the magnetoimpedance are discussed in terms of the radial distribution of the magnetic anisotropy. Accordingly, we demonstrated that the giant magnetoimpedance effect of Co-rich microwires can be tailored by controlling the magnetic anisotropy of Co-rich microwires, using appropriate thermal treatment.
Amorphous soft magnetic microwires have attracted much attention in the area of sensor applicatio... more Amorphous soft magnetic microwires have attracted much attention in the area of sensor applications due to their excellent properties. In this work, we study the influence of annealing treatments (stress and conventional) in the giant magnetoimpedance (GMI) response and the field sensitivity of the soft magnetic Co 69.2 Fe 3.6 Ni 1 B 12.5 Si 11 Mo 1.5 C 1.2 glass-coated microwires. Here we report a remarkable and simultaneous enhancement of GMI effect and field sensitivity. The highest sensitivity of 104%/Oe and the GMI response of 234% were achieved for 300 • C stress-annealed samples at 472 and 236 MPa, respectively. Additionally, we found that stress-annealed microwires exhibit a frequency dependence on maximal GMI response and field sensitivity. These findings are obtained by fine-tuning their magnetoeslastic anisotropies through stress-annealing treatments of as-prepared microwires at the proper temperature and axial applied stress upon annealing. We hope that the results presented here widen the scope of investigations for the future design of soft magnetic materials for sensor purposes.
Thin magnetic wires can present excellent soft magnetic properties (with coercivities up to 4 A/m... more Thin magnetic wires can present excellent soft magnetic properties (with coercivities up to 4 A/m), Giant Magneto-impedance effect, GMI, or rectangular hysteresis loops combined with quite fast domain wall, DW, propagation. In this paper we overview the magnetic properties of thin magnetic wires and post-processing allowing optimization of their magnetic properties for magnetic sensor applications. We concluded that the GMI effect, magnetic softness or DW dynamics of microwires can be tailored by controlling the magnetoelastic anisotropy of as-prepared microwires or controlling their internal stresses and domain structure by appropriate thermal treatment.
We provide an overview of the tools directed to reversible and irreversible transformations of th... more We provide an overview of the tools directed to reversible and irreversible transformations of the magnetic structure of glass-covered microwires. The irreversible tools are the selection of the chemical composition, geometric ratio, and the stress-annealing. For reversible tuning we use the combination of magnetic fields and mechanical stresses. The studies were focused on the giant magnetoimpedance effect and the velocity of the domain walls propagation important for the technological applications. The essential increase of the giant magnetoimpedance effect and the control of the domain wall velocity were achieved as a result of the use of two types of control tools. The performed simulations reflect the real transformation of the helical domain structures experimentally found.
There is a pressing demand to improve the performance of cost-effective soft magnetic materials f... more There is a pressing demand to improve the performance of cost-effective soft magnetic materials for use in high performance sensors and devices. Giant Magneto-impedance effect (GMI), or fast single domain wall (DW) propagation can be observed in properly processed magnetic microwires. In this paper we have identified the routes to obtain microwires with unique combination of magnetic properties allowing observation of fast and single DW propagation and GMI effect in the same microwire. By modifying the annealing conditions, we have found the appropriate regimes allowing achievement of the highest GMI ratio and the fastest DW dynamics. The observed experimental results are discussed considering the radial distribution of magnetic anisotropy and the correlation of GMI effect, and DW dynamics with bulk and surface magnetization processes. Studies of both Fe-and Co-rich microwires, using the magneto-optical Kerr effect, MOKE, provide information on the magnetic structure in the outer shell of microwires. We have demonstrated the existence of the spiral helical structure in both studied microwires. At the same time, torsion mechanical stresses induce helical bistability in the same microwires, which allow us to consider these microwires as materials suitable for sensors based on the large Barkhausen jump.
Cu100−xCoxthin films have been obtained by sputtering (x = 3, 9) and sputter gas aggre-gation (x ... more Cu100−xCoxthin films have been obtained by sputtering (x = 3, 9) and sputter gas aggre-gation (x = 2.5, 7.5) and subsequent annealing at 400◦C for 1 h. We have studied their structural,magnetic, and magnetotransport properties, both for the as-deposited and annealed samples, con-firming the important role of the fabrication method in the properties. The magnetic measurementsand the fitting of the hysteresis loops evidence that as-deposited samples consist of superparam-agnetic (SPM) and/or ferromagnetic clusters, but in the samples obtained by gas aggregation theclusters are greater (with ferromagnetic behavior at room temperature) whereas in the samplesobtained by sputtering, the clusters are smaller and there are also diluted Co atoms in the Cu matrix.The annealing affects negligibly the samples obtained by gas aggregation, but the ones obtainedby sputtering are more affected, appearing greater clusters. This behavior is also reflected in themagnetoresistance (MR) measurements of the samples, with different shapes of the MR curvesdepending on the preparation method: more lineal in the whole range for sputtering, saturationat low fields (about 10 kOe) for gas aggregation. Finally, a Kondo-like minimum in the resistanceversus temperature is found in the samples obtained by sputtering, affected by the magnetic fieldand the annealing. The observed Kondo-like behavior and the influence of annealing on a Kondo-likeminimum in sputtered thin films have been attributed to the presence of diluted Co atoms in the Cumatrix and the Co precipitations from the Co–Cu solid solution upon annealing respectively.
The influence of post-processing conditions on the magnetic properties of amorphous and nanocryst... more The influence of post-processing conditions on the magnetic properties of amorphous and nanocrystalline microwires has been thoroughly analyzed, paying attention to the influence of magnetoelastic, induced and magnetocrystalline anisotropies on the hysteresis loops of Fe-, Ni-, and Co-rich microwires. We showed that magnetic properties of glass-coated microwires can be tuned by the selection of appropriate chemical composition and geometry in as-prepared state or further considerably modified by appropriate post-processing, which consists of either annealing or glass-coated removal. Furthermore, stress-annealing or Joule heating can further effectively modify the magnetic properties of amorphous magnetic microwires owing to induced magnetic anisotropy. Devitrification of microwires can be useful for either magnetic softening or magnetic hardening of the microwires. Depending on the chemical composition of the metallic nucleus and on structural features (grain size, precipitating phases), nanocrystalline microwires can exhibit either soft magnetic properties or semi-hard magnetic properties. We demonstrated that the microwires with coercivities from 1 A/m to 40 kA/m can be prepared.
In this paper, a magnetic microwire-based sensor array embedded under the pavement is proposed as... more In this paper, a magnetic microwire-based sensor array embedded under the pavement is proposed as a weighing system at customs ports of entry. This sensor is made of a cementitious material suitable for embedding within the core of concrete structures prior to curing. The objective of this research is to verify the feasibility of stress monitoring for concrete materials using an array of cement-based stress/strain sensors that have been developed using the magnetic sensing property of an embedded microwire in a cement-based composite. Test results for microwire-based sensors and gauge sensors are compared. The strain sensitivity and their linearity are investigated through experimental testing under compressive loadings. Sensors made of these materials can be designed to satisfy specific needs and reduce costs in the production of sensor aggregates with improved coupling performance, thus avoiding any disturbance to the stress state.
The influence of magnetic anisotropy, post-processing conditions, and defects on the domain wall ... more The influence of magnetic anisotropy, post-processing conditions, and defects on the domain wall (DW) dynamics of amorphous and nanocrystalline Fe-, Ni-, and Co-rich microwires with spontaneous and annealing-induced magnetic bistability has been thoroughly analyzed, with an emphasis placed on the influence of magnetoelastic, induced and magnetocrystalline anisotropies. Minimizing magnetoelastic anisotropy, either by the selection of a chemical composition with a low magnetostriction coefficient or by heat treatment, is an appropriate route for DW dynamics optimization in magnetic microwires. Stress-annealing allows further improvement of DW velocity and hence is a promising method for optimization of DW dynamics in magnetic microwires. The origin of current-driven DW propagation in annealing-induced magnetic bistability is attributed to magnetostatic interaction of outer domain shell with transverse magnetization orientation and inner axially magnetized core. The beneficial influence of the stress-annealing on DW dynamics has been explained considering that it allows increasing of the volume of outer domain shell with transverse magnetization orientation at the expense of decreasing the radius of inner axially magnetized core. Such transverse magnetic anisotropy can similarly affect the DW dynamics as the applied transverse magnetic field and hence is beneficial for DW dynamics optimization. Stress-annealing allows designing the magnetic anisotropy distribution more favorable for the DW dynamics improvement. Results on DW dynamics in various families of nanocrystalline microwires are provided. The role of saturation magnetization on DW mobility improvement is discussed. The DW shape, its correlation with the magnetic anisotropy constant and the microwire diameter, as well as manipulation of the DW shape by induced magnetic anisotropy are discussed. The engineering of DW propagation through local stress-annealing and DW collision is demonstrated.
1 Introduction Amorphous glass-coated Co-rich microwires with metallic core diameter d = 5-15 µm ... more 1 Introduction Amorphous glass-coated Co-rich microwires with metallic core diameter d = 5-15 µm and total diameter D = 10-30 µm are quite promising for various technological applications due to their unique magnetic characteristics, such as Giant Magneto-Impedance effect . It is generally accepted that for amorphous wires the usual magnetocrystalline anisotropy is absent, so that the magnetic anisotropy is related with the residual quenching stress frozen within the wire during fast solidification process. In papers [4, 5] a simple expression for the magneto-elastic energy density of a glass-coated amorphous microwire was suggested. Besides, the residual stress distribution was calculated [5] based on the theory of viscoelasticity . In contrast to the earlier attempts [7-9], this approach takes into account a relaxation of the arising stresses within a certain temperature interval near the point of the wire vitrification. As a result, the stress amplitude calculated in [5] is several times lower than that one estimated in papers [7---9].
Glass-coated magnetic microwires with positive magnetostriction show peculiar domain structure th... more Glass-coated magnetic microwires with positive magnetostriction show peculiar domain structure that consists mostly of one large domain with magnetization-oriented axially. It was shown that small closure domains appear at the end of the microwire in order to decrease the stray fields. As a result of such domain structure, the magnetization reversal in axial direction runs through the depinning of one of such closure domains and subsequent propagation of the corresponding domain wall.
The dynamics of the magnetization reversal by means of headto-head domain-wall propagation is inv... more The dynamics of the magnetization reversal by means of headto-head domain-wall propagation is investigated both experimentally and theoretically for magnetic labels made from Ferich bistable glass-coated microwires. It is shown that the amplitudes of the electromagnetic harmonics generated by bistable Fe-rich magnetic labels of the length 1-4 cm with metallic nuclear diameter of 10-20 mm are more than 5 times larger than that of similar labels made of Co-rich microwires having high permeability and low coercive force. The electromagnetic harmonics can be detected at the distances up to 15-20 cm from the magnetic label at the signal-to-noise ratio not lower than 2.0.
INTERMAG 2006 - IEEE International Magnetics Conference, 2006
The influence of magnetostatic interactions on a wire domain structure is investigated here using... more The influence of magnetostatic interactions on a wire domain structure is investigated here using the simplest possible situation: a) the wire has perfect cylindrical shape, b) the magnetic anisotropy is uniaxial with the easy anisotropy axis parallel to the wire axis, c) the material parameters of the wire correspond to a soft magnetic case, Ms 2GtK1, where Ms is the saturation magnetization and K1 is the anisotropy constant. Axial and circular magnetization processes are studied in detail and the influence of surface defects on the domain wall mobility is considered.
A scanning high-temperature superconducting quantum interference device microscope with spatial r... more A scanning high-temperature superconducting quantum interference device microscope with spatial resolution of about 50 mm and sensitivity of 2 mOe/Hz 1/2 has been used to study stray magnetic fields of glass-coated microwires with compositions Fe 74 B 13 Si 11 C 2 and Co 74 B 13 Si 11 C 2 at T ¼ 77 K. The stray field images have been obtained within a soft magnetic shield (residual magnetic field, H r o1 mOe), as well as with applied magnetic field within the range of 750 Oe. For a Fe-rich microwire, a simple two-pole structure has been observed in the ground state, whereas for a Co-rich microwire the ground state corresponds, probably, to a domain structure with alternating magnetic poles along the wire length. r
The design and performance of a magnetometer based on the offdiagonal GMI effect in Co-rich glass... more The design and performance of a magnetometer based on the offdiagonal GMI effect in Co-rich glass-coated microwire are presented. The sensing element of the magnetometer is a 10-mm long piece of Co-Fe-Ni-B-Si-Mo microwire with a small pick-up coil of 85 turns wounded around the microwire. The electronics with a feedback circuit is used to register an electromotive force proportional to the external magnetic field applied along the wire axis. In the absence of the feedback current the magnetometer is capable of measuring a narrow range of magnetic fields, AE3.5 mT, in the frequency range of 0-1 kHz, the level of the equivalent magnetic noise being about 10 pT Hz À1/2 at a frequency of 300 Hz. The use of the feedback circuit increases the range of the measured magnetic fields up to AE250 mT.
Results on the giant magnetoimpedance (GMI) effect measured at 10 MHz and 500 MHz in an array of ... more Results on the giant magnetoimpedance (GMI) effect measured at 10 MHz and 500 MHz in an array of microwires containing a number of thin Co 59 2 Fe 4 8 Ni 11 B 14 Si 11 amorphous glass-coated microwires are presented. The GMI effect was measured as a function of the number, n, of microwires from 1 till 30 involve in the array. The shape of the GMI field dependence at 10 MHz of a single microwire is typical for the materials with circular magnetic anisotropy, exhibiting a maximum at certain dc axial magnetic field H max . At 10 MHz the GMI ratio of thin microwires array decreases as increasing the number n of microwires of the array. On the other hand, at 500 MHz H m n has an opposite dependence, decreasing with n. The observed phenomena can be understand taking into account the magnetostatic interaction between the microwires placed closely in the array and also as a partial shielding of the applied magnetic field by the microwires. A remarkable difference in the frequency dependence of the GMI effect can be attributed to the frequency dependence of the shielding related with the frequency dependence of the magnetic permeability.
Local nucleation fields of Fe-rich amorphous glass-coated microwires with composition Fe 74 Si 11... more Local nucleation fields of Fe-rich amorphous glass-coated microwires with composition Fe 74 Si 11 B 13 C 2 have been measured along the wire length at different applied tension stresses. From these measurements the ratio l s /M s , where l s is the magnetostriction constant and M s is the saturation magnetization, as well as the amplitude of the residual quenching stresses have been determined for wires with different metal core radius and glass shell thickness. The method enables one to determine also the positions of strong localized defects that reduce considerably the wire nucleation field from its average value. r
The magnetic properties of Co 68 Mn 7 Si 10 B 15 glass coated amorphous microwires of about 16.5 ... more The magnetic properties of Co 68 Mn 7 Si 10 B 15 glass coated amorphous microwires of about 16.5 µm in diameter have been investigated from liquid helium up to room temperature by ferromagnetic resonance at 9.243 GHz. Based on the results of measurements both the magnetic anisotropy constants, the first arising from the stress at the interface between the metallic surface and the coating and the second one of the inner core have been obtained for the room temperature. The effective anisotropy field was determined in the range from the liquid helium to the room temperature.
We study the magnetocaloric effect �MCE� in parallel one-dimensional chains of dipole-dipole inte... more We study the magnetocaloric effect �MCE� in parallel one-dimensional chains of dipole-dipole interacting magnetic nanoparticles with collinear magnetic anisotropy axes. By means of a Monte Carlo method we simulate the magnetic field dependence of the MCE for a field applied perpendicular to the anisotropy axes, finding the coexistence of direct and inverse MCE being both of reversible character. The inverse MCE temperature range is quite small and progressively shifts to lower temperatures with increasing applied field until it disappears, thus we have mainly focused our study on the direct MCE-temperature range. We show the existence of a particular magnetic field value being proportional to the anisotropy field of the particles, H� = �2.5HA, which optimizes the magnetic entropy change and refrigerant capacity of the collinear aligned ensemble of nanoparticles.
Magnetic microwires can present excellent soft magnetic properties and a giant magnetoimpedance e... more Magnetic microwires can present excellent soft magnetic properties and a giant magnetoimpedance effect. In this paper, we present our last results on the effect of postprocessing allowing optimization of the magnetoimpedance effect in Co-rich microwires suitable for magnetic microsensor applications. Giant magnetoimpedance effect improvement was achieved either by annealing or stress-annealing. Annealed Co-rich presents rectangular hysteresis loops. However, an improvement in magnetoimpedance ratio is observed at fairly high annealing temperatures over a wide frequency range. Application of stress during annealing at moderate values of annealing temperatures and stress allows for a remarkable decrease in coercivity and increase in squareness ratio and further giant magnetoimpedance effect improvement. Stress-annealing, carried out at sufficiently high temperatures and/or stress allowed induction of transverse magnetic anisotropy, as well as magnetoimpedance effect improvement. Enhanced magnetoimpedance ratio values for annealed and stress-annealed samples and frequency dependence of the magnetoimpedance are discussed in terms of the radial distribution of the magnetic anisotropy. Accordingly, we demonstrated that the giant magnetoimpedance effect of Co-rich microwires can be tailored by controlling the magnetic anisotropy of Co-rich microwires, using appropriate thermal treatment.
Amorphous soft magnetic microwires have attracted much attention in the area of sensor applicatio... more Amorphous soft magnetic microwires have attracted much attention in the area of sensor applications due to their excellent properties. In this work, we study the influence of annealing treatments (stress and conventional) in the giant magnetoimpedance (GMI) response and the field sensitivity of the soft magnetic Co 69.2 Fe 3.6 Ni 1 B 12.5 Si 11 Mo 1.5 C 1.2 glass-coated microwires. Here we report a remarkable and simultaneous enhancement of GMI effect and field sensitivity. The highest sensitivity of 104%/Oe and the GMI response of 234% were achieved for 300 • C stress-annealed samples at 472 and 236 MPa, respectively. Additionally, we found that stress-annealed microwires exhibit a frequency dependence on maximal GMI response and field sensitivity. These findings are obtained by fine-tuning their magnetoeslastic anisotropies through stress-annealing treatments of as-prepared microwires at the proper temperature and axial applied stress upon annealing. We hope that the results presented here widen the scope of investigations for the future design of soft magnetic materials for sensor purposes.
Thin magnetic wires can present excellent soft magnetic properties (with coercivities up to 4 A/m... more Thin magnetic wires can present excellent soft magnetic properties (with coercivities up to 4 A/m), Giant Magneto-impedance effect, GMI, or rectangular hysteresis loops combined with quite fast domain wall, DW, propagation. In this paper we overview the magnetic properties of thin magnetic wires and post-processing allowing optimization of their magnetic properties for magnetic sensor applications. We concluded that the GMI effect, magnetic softness or DW dynamics of microwires can be tailored by controlling the magnetoelastic anisotropy of as-prepared microwires or controlling their internal stresses and domain structure by appropriate thermal treatment.
We provide an overview of the tools directed to reversible and irreversible transformations of th... more We provide an overview of the tools directed to reversible and irreversible transformations of the magnetic structure of glass-covered microwires. The irreversible tools are the selection of the chemical composition, geometric ratio, and the stress-annealing. For reversible tuning we use the combination of magnetic fields and mechanical stresses. The studies were focused on the giant magnetoimpedance effect and the velocity of the domain walls propagation important for the technological applications. The essential increase of the giant magnetoimpedance effect and the control of the domain wall velocity were achieved as a result of the use of two types of control tools. The performed simulations reflect the real transformation of the helical domain structures experimentally found.
There is a pressing demand to improve the performance of cost-effective soft magnetic materials f... more There is a pressing demand to improve the performance of cost-effective soft magnetic materials for use in high performance sensors and devices. Giant Magneto-impedance effect (GMI), or fast single domain wall (DW) propagation can be observed in properly processed magnetic microwires. In this paper we have identified the routes to obtain microwires with unique combination of magnetic properties allowing observation of fast and single DW propagation and GMI effect in the same microwire. By modifying the annealing conditions, we have found the appropriate regimes allowing achievement of the highest GMI ratio and the fastest DW dynamics. The observed experimental results are discussed considering the radial distribution of magnetic anisotropy and the correlation of GMI effect, and DW dynamics with bulk and surface magnetization processes. Studies of both Fe-and Co-rich microwires, using the magneto-optical Kerr effect, MOKE, provide information on the magnetic structure in the outer shell of microwires. We have demonstrated the existence of the spiral helical structure in both studied microwires. At the same time, torsion mechanical stresses induce helical bistability in the same microwires, which allow us to consider these microwires as materials suitable for sensors based on the large Barkhausen jump.
Cu100−xCoxthin films have been obtained by sputtering (x = 3, 9) and sputter gas aggre-gation (x ... more Cu100−xCoxthin films have been obtained by sputtering (x = 3, 9) and sputter gas aggre-gation (x = 2.5, 7.5) and subsequent annealing at 400◦C for 1 h. We have studied their structural,magnetic, and magnetotransport properties, both for the as-deposited and annealed samples, con-firming the important role of the fabrication method in the properties. The magnetic measurementsand the fitting of the hysteresis loops evidence that as-deposited samples consist of superparam-agnetic (SPM) and/or ferromagnetic clusters, but in the samples obtained by gas aggregation theclusters are greater (with ferromagnetic behavior at room temperature) whereas in the samplesobtained by sputtering, the clusters are smaller and there are also diluted Co atoms in the Cu matrix.The annealing affects negligibly the samples obtained by gas aggregation, but the ones obtainedby sputtering are more affected, appearing greater clusters. This behavior is also reflected in themagnetoresistance (MR) measurements of the samples, with different shapes of the MR curvesdepending on the preparation method: more lineal in the whole range for sputtering, saturationat low fields (about 10 kOe) for gas aggregation. Finally, a Kondo-like minimum in the resistanceversus temperature is found in the samples obtained by sputtering, affected by the magnetic fieldand the annealing. The observed Kondo-like behavior and the influence of annealing on a Kondo-likeminimum in sputtered thin films have been attributed to the presence of diluted Co atoms in the Cumatrix and the Co precipitations from the Co–Cu solid solution upon annealing respectively.
The influence of post-processing conditions on the magnetic properties of amorphous and nanocryst... more The influence of post-processing conditions on the magnetic properties of amorphous and nanocrystalline microwires has been thoroughly analyzed, paying attention to the influence of magnetoelastic, induced and magnetocrystalline anisotropies on the hysteresis loops of Fe-, Ni-, and Co-rich microwires. We showed that magnetic properties of glass-coated microwires can be tuned by the selection of appropriate chemical composition and geometry in as-prepared state or further considerably modified by appropriate post-processing, which consists of either annealing or glass-coated removal. Furthermore, stress-annealing or Joule heating can further effectively modify the magnetic properties of amorphous magnetic microwires owing to induced magnetic anisotropy. Devitrification of microwires can be useful for either magnetic softening or magnetic hardening of the microwires. Depending on the chemical composition of the metallic nucleus and on structural features (grain size, precipitating phases), nanocrystalline microwires can exhibit either soft magnetic properties or semi-hard magnetic properties. We demonstrated that the microwires with coercivities from 1 A/m to 40 kA/m can be prepared.
In this paper, a magnetic microwire-based sensor array embedded under the pavement is proposed as... more In this paper, a magnetic microwire-based sensor array embedded under the pavement is proposed as a weighing system at customs ports of entry. This sensor is made of a cementitious material suitable for embedding within the core of concrete structures prior to curing. The objective of this research is to verify the feasibility of stress monitoring for concrete materials using an array of cement-based stress/strain sensors that have been developed using the magnetic sensing property of an embedded microwire in a cement-based composite. Test results for microwire-based sensors and gauge sensors are compared. The strain sensitivity and their linearity are investigated through experimental testing under compressive loadings. Sensors made of these materials can be designed to satisfy specific needs and reduce costs in the production of sensor aggregates with improved coupling performance, thus avoiding any disturbance to the stress state.
The influence of magnetic anisotropy, post-processing conditions, and defects on the domain wall ... more The influence of magnetic anisotropy, post-processing conditions, and defects on the domain wall (DW) dynamics of amorphous and nanocrystalline Fe-, Ni-, and Co-rich microwires with spontaneous and annealing-induced magnetic bistability has been thoroughly analyzed, with an emphasis placed on the influence of magnetoelastic, induced and magnetocrystalline anisotropies. Minimizing magnetoelastic anisotropy, either by the selection of a chemical composition with a low magnetostriction coefficient or by heat treatment, is an appropriate route for DW dynamics optimization in magnetic microwires. Stress-annealing allows further improvement of DW velocity and hence is a promising method for optimization of DW dynamics in magnetic microwires. The origin of current-driven DW propagation in annealing-induced magnetic bistability is attributed to magnetostatic interaction of outer domain shell with transverse magnetization orientation and inner axially magnetized core. The beneficial influence of the stress-annealing on DW dynamics has been explained considering that it allows increasing of the volume of outer domain shell with transverse magnetization orientation at the expense of decreasing the radius of inner axially magnetized core. Such transverse magnetic anisotropy can similarly affect the DW dynamics as the applied transverse magnetic field and hence is beneficial for DW dynamics optimization. Stress-annealing allows designing the magnetic anisotropy distribution more favorable for the DW dynamics improvement. Results on DW dynamics in various families of nanocrystalline microwires are provided. The role of saturation magnetization on DW mobility improvement is discussed. The DW shape, its correlation with the magnetic anisotropy constant and the microwire diameter, as well as manipulation of the DW shape by induced magnetic anisotropy are discussed. The engineering of DW propagation through local stress-annealing and DW collision is demonstrated.
1 Introduction Amorphous glass-coated Co-rich microwires with metallic core diameter d = 5-15 µm ... more 1 Introduction Amorphous glass-coated Co-rich microwires with metallic core diameter d = 5-15 µm and total diameter D = 10-30 µm are quite promising for various technological applications due to their unique magnetic characteristics, such as Giant Magneto-Impedance effect . It is generally accepted that for amorphous wires the usual magnetocrystalline anisotropy is absent, so that the magnetic anisotropy is related with the residual quenching stress frozen within the wire during fast solidification process. In papers [4, 5] a simple expression for the magneto-elastic energy density of a glass-coated amorphous microwire was suggested. Besides, the residual stress distribution was calculated [5] based on the theory of viscoelasticity . In contrast to the earlier attempts [7-9], this approach takes into account a relaxation of the arising stresses within a certain temperature interval near the point of the wire vitrification. As a result, the stress amplitude calculated in [5] is several times lower than that one estimated in papers [7---9].
Glass-coated magnetic microwires with positive magnetostriction show peculiar domain structure th... more Glass-coated magnetic microwires with positive magnetostriction show peculiar domain structure that consists mostly of one large domain with magnetization-oriented axially. It was shown that small closure domains appear at the end of the microwire in order to decrease the stray fields. As a result of such domain structure, the magnetization reversal in axial direction runs through the depinning of one of such closure domains and subsequent propagation of the corresponding domain wall.
The dynamics of the magnetization reversal by means of headto-head domain-wall propagation is inv... more The dynamics of the magnetization reversal by means of headto-head domain-wall propagation is investigated both experimentally and theoretically for magnetic labels made from Ferich bistable glass-coated microwires. It is shown that the amplitudes of the electromagnetic harmonics generated by bistable Fe-rich magnetic labels of the length 1-4 cm with metallic nuclear diameter of 10-20 mm are more than 5 times larger than that of similar labels made of Co-rich microwires having high permeability and low coercive force. The electromagnetic harmonics can be detected at the distances up to 15-20 cm from the magnetic label at the signal-to-noise ratio not lower than 2.0.
INTERMAG 2006 - IEEE International Magnetics Conference, 2006
The influence of magnetostatic interactions on a wire domain structure is investigated here using... more The influence of magnetostatic interactions on a wire domain structure is investigated here using the simplest possible situation: a) the wire has perfect cylindrical shape, b) the magnetic anisotropy is uniaxial with the easy anisotropy axis parallel to the wire axis, c) the material parameters of the wire correspond to a soft magnetic case, Ms 2GtK1, where Ms is the saturation magnetization and K1 is the anisotropy constant. Axial and circular magnetization processes are studied in detail and the influence of surface defects on the domain wall mobility is considered.
A scanning high-temperature superconducting quantum interference device microscope with spatial r... more A scanning high-temperature superconducting quantum interference device microscope with spatial resolution of about 50 mm and sensitivity of 2 mOe/Hz 1/2 has been used to study stray magnetic fields of glass-coated microwires with compositions Fe 74 B 13 Si 11 C 2 and Co 74 B 13 Si 11 C 2 at T ¼ 77 K. The stray field images have been obtained within a soft magnetic shield (residual magnetic field, H r o1 mOe), as well as with applied magnetic field within the range of 750 Oe. For a Fe-rich microwire, a simple two-pole structure has been observed in the ground state, whereas for a Co-rich microwire the ground state corresponds, probably, to a domain structure with alternating magnetic poles along the wire length. r
The design and performance of a magnetometer based on the offdiagonal GMI effect in Co-rich glass... more The design and performance of a magnetometer based on the offdiagonal GMI effect in Co-rich glass-coated microwire are presented. The sensing element of the magnetometer is a 10-mm long piece of Co-Fe-Ni-B-Si-Mo microwire with a small pick-up coil of 85 turns wounded around the microwire. The electronics with a feedback circuit is used to register an electromotive force proportional to the external magnetic field applied along the wire axis. In the absence of the feedback current the magnetometer is capable of measuring a narrow range of magnetic fields, AE3.5 mT, in the frequency range of 0-1 kHz, the level of the equivalent magnetic noise being about 10 pT Hz À1/2 at a frequency of 300 Hz. The use of the feedback circuit increases the range of the measured magnetic fields up to AE250 mT.
Results on the giant magnetoimpedance (GMI) effect measured at 10 MHz and 500 MHz in an array of ... more Results on the giant magnetoimpedance (GMI) effect measured at 10 MHz and 500 MHz in an array of microwires containing a number of thin Co 59 2 Fe 4 8 Ni 11 B 14 Si 11 amorphous glass-coated microwires are presented. The GMI effect was measured as a function of the number, n, of microwires from 1 till 30 involve in the array. The shape of the GMI field dependence at 10 MHz of a single microwire is typical for the materials with circular magnetic anisotropy, exhibiting a maximum at certain dc axial magnetic field H max . At 10 MHz the GMI ratio of thin microwires array decreases as increasing the number n of microwires of the array. On the other hand, at 500 MHz H m n has an opposite dependence, decreasing with n. The observed phenomena can be understand taking into account the magnetostatic interaction between the microwires placed closely in the array and also as a partial shielding of the applied magnetic field by the microwires. A remarkable difference in the frequency dependence of the GMI effect can be attributed to the frequency dependence of the shielding related with the frequency dependence of the magnetic permeability.
Local nucleation fields of Fe-rich amorphous glass-coated microwires with composition Fe 74 Si 11... more Local nucleation fields of Fe-rich amorphous glass-coated microwires with composition Fe 74 Si 11 B 13 C 2 have been measured along the wire length at different applied tension stresses. From these measurements the ratio l s /M s , where l s is the magnetostriction constant and M s is the saturation magnetization, as well as the amplitude of the residual quenching stresses have been determined for wires with different metal core radius and glass shell thickness. The method enables one to determine also the positions of strong localized defects that reduce considerably the wire nucleation field from its average value. r
The magnetic properties of Co 68 Mn 7 Si 10 B 15 glass coated amorphous microwires of about 16.5 ... more The magnetic properties of Co 68 Mn 7 Si 10 B 15 glass coated amorphous microwires of about 16.5 µm in diameter have been investigated from liquid helium up to room temperature by ferromagnetic resonance at 9.243 GHz. Based on the results of measurements both the magnetic anisotropy constants, the first arising from the stress at the interface between the metallic surface and the coating and the second one of the inner core have been obtained for the room temperature. The effective anisotropy field was determined in the range from the liquid helium to the room temperature.
We study the magnetocaloric effect �MCE� in parallel one-dimensional chains of dipole-dipole inte... more We study the magnetocaloric effect �MCE� in parallel one-dimensional chains of dipole-dipole interacting magnetic nanoparticles with collinear magnetic anisotropy axes. By means of a Monte Carlo method we simulate the magnetic field dependence of the MCE for a field applied perpendicular to the anisotropy axes, finding the coexistence of direct and inverse MCE being both of reversible character. The inverse MCE temperature range is quite small and progressively shifts to lower temperatures with increasing applied field until it disappears, thus we have mainly focused our study on the direct MCE-temperature range. We show the existence of a particular magnetic field value being proportional to the anisotropy field of the particles, H� = �2.5HA, which optimizes the magnetic entropy change and refrigerant capacity of the collinear aligned ensemble of nanoparticles.
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Papers by Arcady Zhukov