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We have investigated the effect of dc bias current IB on longitudinal magnetoimpedance (MI) in amorphous microwire with helical anisotropy and experimentally demonstrated that, by changing the dc current IB, it is possible to considerably affect the MI dependence. We propose to use this effect in developing a longitudinal MI sensor that overcomes the drawbacks usually associated with the longitudinal MI-namely the impossibility to determine the direction of an external axial magnetic field HE and the low sensitivity near the zero-field point. We demonstrate that a set of two measurements of longitudinal wire impedance with properly selected bias current IB allows determination of both the magnitude and direction of the magnetic field HE over an extended range, much higher than the sample anisotropy field. Additional features of the proposed method are the increased sensitivity and the detection of exceeding the operating range. [ABSTRACT FROM AUTHOR]

We present a study of magnetic properties of single-crystal Co3O4 nanowires with diameter about 7 nm. The nanowires expose (111) planes composed of plenty of Co3+ cations and exhibit two order temperatures at 56 K (TN of wire cores) and 73 K (order temperature of wire shells), which are far above TN = 40 K of bulk Co3O4. This novel behavior is attributed to symmetry breaking of surface Co3+ cations and magnetic proximity effect. The nanowire shells show macroscopic residual magnetic moments. Cooling in a magnetic field, a fraction of the residual moments are tightly pinned to the antiferromagnetic lattice, which results in an obvious horizontal and vertical shift of hysteresis loop. Our experiment demonstrates that the exchange bias field HE and the pinned magnetic moments Mpin follow a simple expression HE = aMpin with a a constant. [ABSTRACT FROM AUTHOR]

A theoretical investigation on the anisotropic magnetization and Faraday rotation of paramagnetic ytterbium gallium garnet (YbGaG) is presented when the external magnetic fields are parallel to the [100], [110], and [111] crystallographic directions at above 4.2 K. Here, only considering the crystal field effect, we demonstrate that the anisotropies of magnetization M become more obvious with the increase of the applied magnetic fields. Meanwhile, at 4.2 K, M approaches saturation when the applied magnetic field He is up to 300 kOe in YbGaG. Particularly, this paper further confirms that the Yb–Yb exchange interaction greatly affects on the magnetic and magneto-optical properties in paramagnetic YbGaG. Moreover, it is suggested that the exchange interaction show an obvious isotropy and temperature dependence. The theoretical explanation of magnetic and magneto-optical anisotropy in YbGaG to the available experimental results is obtained. [ABSTRACT FROM AUTHOR]

We prepared several heterostructures, Co/Bi0.90La0.10FeO3 on surface oxidized Si or (111) SrTiO3 and NiFe/Bi0.90La0.10FeO3 on (001) SrTiO3 substrates using LaNiO3 as bottom electrode. With different strategies of voltage application, the exchange bias field HE decreased with increasing voltage irreversibly for all the heterostructures at room temperature. The chemical state at the NiFe/Bi0.90La0.10FeO3 interface was studied by X-ray photoelectron spectroscopy before and after the electrical manipulation. The oxidization of the metallic ferromagnetic layer at interface after the electrical manipulation has been confirmed, which might explain the irreversibility. [ABSTRACT FROM AUTHOR]

In this study, FeMn was introduced as an antiferromagnetic (AFM) layer to couple with a singlelayered Co49Pt51 alloy thin film, and it was compared with a Co49Pt51/IrMn bilayer system in exchange bias (EB) effect, to explore the mechanism of spontaneous perpendicular exchange bias (PEB), which has been recently observed in CoPt/IrMn bilayers. Bilayers of CoPt/IrMn and CoPt/ FeMn were prepared under the same conditions by sputtering at room temperature without any inducing field. Although PEB was observed in as-grown CoPt/FeMn bilayers, the loop shape and PEB behavior were found to exhibit different characteristics from those of CoPt/IrMn bilayers. The CoPt (5 nm)/FeMn (10 nm) bilayer has a sheared loop that is similar to a double-shifted loop and a much lower squareness ratio (SQR=0.52) and exchange bias field (He=180 Oe) than the CoPt (5 nm)/IrMn (10 nm) system, which has a rectangular loop shape and a high SQR of 0.97 and large He of 290 Oe. The two systems present entirely different dependences of PEB on the thickness of the AFM layer. CoPt/IrMn exhibits behavior that is typical of most EB systems, but for CoPt/ FeMn, this dependence is more complicated with an unusual peak at an AFM layer thickness of 10 nm. Based on the dissimilar loop shapes and dependences of PEB on AFM thickness, the mechanisms of the spontaneously established PEB in these two systems are considered to differ. Investigations of cross-sectional transmission electron microscopy revealed no apparent difference between the interfacial microstructures of the two systems. X-ray diffraction studies demonstrated the <111> texture of both systems. Therefore, different interfacial spin configurations may be responsible for the dissimilar PEB behaviors in these two FM/AFM bilayer systems. [ABSTRACT FROM AUTHOR]

In this work, we have investigated the temperature dependence and effect of seed layer thickness on the exchange bias of a Ni80Fe20 (ts)/Fe50Mn50 (20 nm)/Ni80Fe20 (20 nm) trilayer, with ts varied systematically from 5 to 50 nm. Room temperature hysteresis loops show that variation in ts strongly affects the exchange bias of both the seed and top Ni80Fe20 layers. Magnetotransport measurements were used to determine the temperature dependence of the overall exchange field (HE) and coercivity (HC) as a function of seed layer thickness. [ABSTRACT FROM AUTHOR]

By coupling an artificial antiferromagnet (AAF)(CoFe/Ru/CoFe) to a ferro-/antiferromagnet (F/AF) system (NiFe/IrMn) we found a strong increase of the exchange bias blocking temperature, e.g., at 1.5-nm IrMn from 110 to 360 K. By magneto-optical Kerr effect and torquemetry at 10-340 K we determined the exchange bias field He, the coupling energy JF/AF between ferromagnet and antiferromagnet, and the rotational loss for thickness of IrMn from (0.3 to 3.5) nm. By comparison of both systems we concluded that for small thickness of the AF its superparamagnetic state was overcome due to the increased total anisotropy energy in the system with AAF. In this system exchange bias can be realized at room temperature with vanishing crystalline anisotropy of the antiferromagnet and without rotational loss. [ABSTRACT FROM AUTHOR]

The effect of grain size modulation on exchange bias effect in CE-type antiferromagnetic Sm0.5Ca0.5MnO3 phase separated manganite is reported here. With the reduction of particle size, ferromagnetic clusters are found to form in the charge ordered antiferromagnetic matrix and gradually become larger. The horizontal and vertical shifts of the magnetic hysteresis loops in the field cooled magnetization process clearly indicate the size dependent exchange bias effect and it can be tuned with the reduction of particle sizes. The values of exchange bias parameter, i.e., exchange bias field (HE), coercivity (HC), remanence asymmetry (ME), and magnetic coercivity (MC) are found to depend strongly on the particle size. The variations of HE follow non-monotonic dependencies with reduction in particle size and show maximum (1205 Oe) at particle size of 150 nm at T=5K, which can be ascribed due to the changes in uncompensated surface spins. The values of HE and ME are found to decrease exponentially with increasing temperature below the spin- or cluster-glass like freezing temperature. The spin relaxation model has been employed for analysis of large magnetic training effect. The linear relationship between HE and ME further confirms the role of uncompensated surface spins. In view of spintronics application of manganites, the present observation of large exchange bias shift in this half-doped manganite may have great technological importance. [ABSTRACT FROM AUTHOR]

Fe81Ga19 films were deposited on Si(100) substrates at room temperature by the dc magnetron sputtering method. Each film sample was rectangular: the length (L) and the width (w). From the curvature measurement on the film surface, we found that the principal stresses in the film are compressive and anisotropic. Based on the magneto-elastic theory, the true easy axis of the Fe81Ga19/Si(100) film should be parallel to the minimum stress axis. In addition, we discovered that the Fe81Ga19/Si(100) film is an inverted film (i.e., its HC is larger than HK, where HC is the coercive force and HK is the anisotropy field). The magnetic domain (MD) structures were examined with a magnetic force microscope. After the external field HE (parallel to L) was increased to saturation and then decreased to zero, the MD pattern showed the labyrinth structure. [ABSTRACT FROM AUTHOR]

Pressure effect on magnetic properties of La0.9Ba0.1CoO3 cobaltite, exhibiting the ferromagnetic (FM) cluster-glass behavior and exchange bias (EB) effect at low temperatures, was investigated up to 10 kbar. It was found that an applied pressure increases the temperature TCcl ≈ 190 K, below which the FM clusters appear, and enlarges the FM phase volume in the sample. Positive value of dTCcl/dP coefficient suggests a wide eg-electron bandwidth for Co ions sited inside the Ba-rich regions (FM clusters). The EB field HE increases sharply with decreasing temperature below the spin-glass (SG) like transition temperature Tf ≈ 38 K, in a consequence of the exchange coupling at the FM/SG interfaces. Applied pressure was found to suppress strongly the EB, in particular, HE reduces by a factor of ∼3 under pressure of 10 kbar at 30 K. It appears that under pressure, HE varies oppositely to the changes in FM phase volume that is very similar to the behavior observed for phase-separated FM/antiferromagnetic manganites. Overall, the pressure-induced diminution in HE is explained by considering an increase of the FM cluster size and by concomitant decrease of distance between clusters. The results show that for phase-separated FM/SG cobaltites, the EB effect may be controlled by external pressure. [ABSTRACT FROM AUTHOR]

We investigated the effects of induced helical anisotropy and application of dc bias current IB on longitudinal magnetoimpedance (MI) in amorphous microwires both separately and together. We demonstrated that when both parameters are present, i.e., a dc bias current IB is applied to the microwire with induced helical anisotropy, the longitudinal MI sensor range can be considerably extended up to the fields considerably higher than its anisotropy field as the slope of MI curve dZ/dHE remains rather high. A highly asymmetric longitudinal MI dependence with a rather high slope at the zero-field point was obtained. Reversing the bias current IB causes reversal of the bias field direction and results in a mirroring of the MI dependence. This gives a possibility to determine both the sign and the magnitude of the external magnetic field. The obtained results can be used in development of the longitudinal MI sensors with increased sensitivity and/or range. [ABSTRACT FROM AUTHOR]

(Fe81-xCoxGa19)80B20 ribbons, with x = 0, 7, 11, 19, and 23, were made by the single-roller quenching method. The x-ray diffraction patterns showed the A2, D019, and L12 diffraction peaks coexisting with the amorphous matrix background. When Fe was replaced by Co, i.e., when x was increased, the first crystallization temperature (TX1) and Curie temperature (TC1) rose greatly. With a sufficiently heavy load (or weight) stretching the ribbon downward, the magnetization MS was pulled along the vertical direction (i.e., the tension-axis). Then, by applying a horizontal field (HE) up to 6 KOe, we determined the sign and magnitude of the saturation magnetostriction (λS). The Young's modulus (ES) at magnetization saturation and ΔE effect was estimated from the stress-strain curve. We discovered that the stress-strain curve of (Fe81Ga19)80B20 exhibits the auxetic (or abnormal) characteristic with ΔE < 0. For the rest of the (Fe81-xCoxGa19)80B20 with x ≠ 0, their stress-strain curves are normal with ΔE > 0. Because the sign of λS of the A2 phase is opposite to that of the D019 and L12 phases, λS of (Fe81-xCoxGa19)80B20 is much reduced. However, ΔE/E0 ≒ 36% is quite large for (Fe58Co23Ga19)80B20. [ABSTRACT FROM AUTHOR]

Rotational magnetization curves of the exchange-bias bilayers were investigated based on the Stoner-Wohlfarth model, which can be grouped into three cases according to the magnetization reversal process. The unidirectional anisotropic field HE = 41.4 Oe, the uniaxial anisotropic field Hk = 4.2 Oe and the accurate direction of the easy axis of our FeNi/FeMn exchange-bias bilayers were obtained by fitting their experimental rotational magnetization curves. During the rotational process the magnetization reversal of the bilayers is a coherent rotation with a critical magnetization reversal field H1 = 41.372 Oe. [ABSTRACT FROM AUTHOR]

The magnetic NiO/Fe19Ni81 nanostructure bilayer is deposited onto the colloidal spheres grown on a Si wafer by the self-assembly technology. The nanocap and the nanodot arrays form on the spherical surface and the Si substrate, respectively, which are confirmed by scanning electron microscopy and transmission electron microscopy measurements. Compared to the flat bilayer with the same composition deposited on the Si substrate, the exchange bias field HE from the nanocap is twice as large. The enhancement of HE in the nanocap is ascribed to the decreased thickness of the ferromagnetic layer induced by the sphere surface. The size and space of the biased caps are estimated based on the thickness variations induced by the sphere surfaces. [ABSTRACT FROM AUTHOR]

The structure, phase components, and magnetic properties of antiferromagnetic coupled Fe2O3 and NiO nanocomposites have been investigated. A negative exchange bias field of about 2 kOe and the anomalous shape of hysteresis loop are observed, which may be related to uncompensated and pinned antiferromagnetic spins at the interface between ferrimagnetic and antiferromagnetic phases in the powders. Furthermore, the exchange bias field varies with the strength of cooling field, and the exchange bias field HE of 0.76 kOe is observed in antiferromagnetic-antiferromagnetic system. [ABSTRACT FROM AUTHOR]

In this article, we theoretically investigate the magnetic and magneto-optical properties of Nd3Ga5O12 in high magnetic fields (up to 35 T). Here, in view of the antiferromagnetism below the Néel temperature, a particular consideration of two magnetic sublattices A and B in Nd3Ga5O12 is presented. Taking account of the indirect exchange interaction, the complicated nonlinearity of magnetization (M) with the external magnetic field (He) is quantitatively described. In addition, we detailedly deduce the relation of Faraday rotation (θF) with the external magnetic fields. In our theoretical model, it is emphasized that θF strongly depends on the magnetization of the two different magnetic sublattices (MA and MB) and He. Referring to the values of MA and MB, the Faraday rotations are simulated at four different wavelengths in Nd3Ga5O12. Our theoretical results can excellently fit the experimental work by Guillot. [ABSTRACT FROM AUTHOR]

Magnetization curves are predicted for a magnetic-tunnel-junction-like system in some special cases of interest: (i) weak interlayer magnetic coupling/high exchange anisotropy field HE and (ii) strong coupling/low HE. Analytical expressions for different switching fields are derived in these situations. These fields depend on the magnetizations (MA,MB) and thicknesses (tA,tB) of the two ferromagnetic layers, on the bilinear (J1) and biquadratic (J2) coupling parameters, and on the exchange (HE) and uniaxial (HA) anisotropy fields of the pinned layer. In the first case, the whole system is found to behave as two uncoupled layers with equivalent exchange and planar anisotropy fields. The effect of the biquadratic coupling J2 on the hysteresis curves is discussed for both ferromagnetic and antiferromagnetic coupling cases. In the second case, the system behaves as a single (ferromagnetic/antiferromagnetic) bilayer with effective exchange and magnetocrystalline anisotropy fields. These findings confirm some of the results inferred from a ferromagnetic resonance analysis and previously reported. [ABSTRACT FROM AUTHOR]

Antiferromagnetic (AF) FeSn2(001) epitaxial and polycrystalline layers were grown in ultrahigh vacuum under various conditions on clean InSb(001) substrates and covered by polycrystalline ferromagnetic Fe layers, forming a new system with exchange bias. Isotopically enriched 57Fe- and 57FeSn2-tracer layers were placed on either side of the Fe/FeSn2 interface for a microscopic investigation of the spin structure and atomic interdiffusion phenomena in near-interfacial regions by 57Fe conversion electron Mössbauer spectroscopy (CEMS) at room temperature and T=10 K. Several spectral components, assigned to pure bcc Fe, Sn-containing bcc Fe, AF-ordered FeSn2, and paramagnetic FeSn2 were resolved in the CEM spectra. Evidence is provided for interdiffusion across the interface. The temperature dependence of the exchange-bias field HE was measured by magnetometry. The CEMS data provide evidence for a correlation between HE at low T and chemical disorder (defects) in the FeSn2 films via the intensity of the paramagnetic line. These results support the assumption that exchange bias is related to the presence of AF domains formed via magnetic defects in the antiferromagnet. The T dependence of HE suggests interfacial exchange-coupling energies higher than the AF wall energy. [ABSTRACT FROM AUTHOR]

A magneto-optical Kerr effect system with a spatial resolution of 2 μm was used to measure the local M-H loops for the free layer of a magnetic tunnel junction with a structure of Ta/Cu/Ta/NiFe/Cu/Mn75Ir25/Co70Fe30/Al2O3/Co70Fe30/Ta to investigate the exchange bias field HE and the coercivity HC for the free layer. The HE and HC measured along the direction of the free layer varied symmetrically with respect to the junction center. The measurements indicate that the enhanced HC correlated with HE, and HE could be reasonably explained by using an “orange-peel-type” coupling based on variations in the thickness of the pinned layer along the direction of the free layer. The variation in HE along the pinned-layer’s direction could be ascribed to that of the free-layer’s thickness, and the increase in HE at the junction edge along the pinned layer was due to a decrease in the thickness of the free layer near the edge. However, the nearly constant HC along the pinned layer indicates that the thickness of the free layer can be excluded from the mechanism for enhancing HC, which is a unique difference in the parameters involved in HE and HC, and in the mechanism for enhancing HC. [ABSTRACT FROM AUTHOR]

Off-aligned exchange coupling in bilayer thin film is investigated by torque curve and ferromagnetic resonance (FMR). In off-aligned exchange coupling, the unidirectional anisotropy axis makes an angle β with the anisotropy axis of the ferromagnetic layer. The torque curves of the off-aligned exchange are shifted with respect to the ones of the aligned case (β=0). From the experimental measure of the shift angle α[sub 0] and of the torque curve slope at α[sub 0], one can determine independently the exchange anisotropy field H[sub E] and β values. A description of the FMR modes in such an off-aligned exchange coupling is given. The FMR mode position and linewidth are studied as a function of the anisotropy fields, of the off-aligned angle values, and of the applied field direction. The resonance frequency and frequency linewidth present particular features which will help to do the right interpretation of FMR spectra of these systems. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Giant magnetostrictive material (GMM) is well known for its hysteresis behaviors related to multiple influencing factors, such as bias magnetic field and excitation level. This feature greatly challenges the loss prediction of giant magnetostrictive transducers. The existing loss prediction models need further improvement to cover the sensitive magnetic properties of GMM. In this paper, the variations of the iron losses with the operation conditions are interpreted by the variations of the Jiles–Atherton model parameters, and a concise parameter identification procedure with great generalizability is proposed. The iron losses of Terfenol-D under variable excitation levels and the DC biases are further investigated. With the proposed procedure, the introduced eight additional modification parameters for the original Jiles–Atherton model are easy to obtain, and merely a few hysteresis loops of Terfenol-D are involved. An experimental setup is established for further demonstration. Comparisons between the measured and calculated results indicate the effectiveness of the proposed approach. Throughout the bias-excitation space within the frequency range under investigation, the iron losses can be precisely estimated with an acceptable error of less than 5%. [ABSTRACT FROM AUTHOR]

The exchange bias phenomena associated with the magnetic glass state at low temperatures in Gd5Ge4 are studied. The exchange bias effect originates from the exchange coupling between the ferromagnetic islands and antiferromagnetic matrix in the magnetic glass state. It is found that the exchange bias in Gd5Ge4 is strongly dependent on the measuring field and the cooling field, which indicates that the antiferromagnetic matrix can be easily transformed into ferromagnetic phase under the applied field. The temperature dependence of the exchange bias field shows that the fluctuation of the temperature has less effect on the exchange bias in the low temperature range. [ABSTRACT FROM AUTHOR]

We report the antiferromagnetic (AFM) thickness dependence study of zinc-blende CrTe/ZnTe/ MnTe layered structure grown on GaAs (100) by low temperature molecular beam epitaxy. The coercivity (HC) and exchange bias field (HE) show a nonmonotonic dependence on the AFM thickness. Both (HC) and HE exhibit a maximum value at the AFM thickness of ∼15 nm. With decreasing AFM thickness, we found that the blocking temperature drops from 70 (Néel temperature of bulk MnTe) to 22 K, while the Curie temperature is found to increase from 100 to 190 K. Additionally, a vertical magnetization shift is observed in the M-H loop, which can be attributed to the presence of frozen ferromagnetic spins at the interface. [ABSTRACT FROM AUTHOR]

The exchange bias effect in Co (25 nm)/Co (5 nm)/Cu (2 nm) nanowire arrays has been systematically investigated. The exchange bias field HE is strongly dependent on the orientation of field cooling relative to the easy axis of the nanowires. We have exploited the competition between field cooling induced unidirectional anisotropy and shape anisotropy of the nanowires to tune both the direction and magnitude of exchange bias. A strong interplay between thermal activation effects and CoO domain size confinement in the nanowires also results in HE for the nanowire arrays being either smaller or larger than the continuous film. [ABSTRACT FROM AUTHOR]

We present the results on the exchange coupling in the zinc-blende CrTe/spacer/MnTe structure with ZnTe acting as a spacer layer (SL). The magnetic hysteresis (M-H) loops show significant shifts in both horizontal and vertical directions. A nonmonotonic variation of the exchange bias field (HE) and coercivity (HC) with the SL thickness is observed. The Curie temperature decreases as the SL thickness increases. The maximum of HE and HC values occur at a SL thickness of 12 ML (monolayer). Strikingly, the exchange coupling remains noticeable even the thickness of SL reaches 24 ML. The exchange bias field and vertical shift are discussed on the basis of frozen ferromagnetic moment model. [ABSTRACT FROM AUTHOR]

We theoretically exploit a class of one-dimensional double-layer photonic crystals based on colloidal ferrofluids, which are made of ferromagnetic nanoparticles suspended in a carrier liquid. Depending on the magnetic-field-induced anisotropic property of the ferrofluid, precise controllability of the band gaps is demonstrated to be possible by applying an appropriate external magnetic field. [ABSTRACT FROM AUTHOR]

The magnetization reversal in exchange biased FeF2/Co films was studied using polarized neutron reflectometry and magneto-optical imaging (MOI). After field cooling in a field H perpendicular to the c axis (the easy axis of FeF2) through the FeF2 Néel temperature, the magnetization curve measured with H parallel to the c axis showed a double loop, one with a positive exchange bias field (HE) and one with a negative HE. This behavior suggests that the antiferromagnet (AFM) is split into two types of domains with HE in opposite directions along the c axis. However, the observation of spin-flip reflectivity in the field region separating the two loops indicates that some rotation of the Co magnetization also occurred during reversal. Concurrently, small inhomogeneous domains with sizes much less than 30 μm were observed using MOI. This implies that small AFM domains with opposing HE created during cooling and the resulting frustration of the interface exchange interaction with the ferromagnet are responsible for the perpendicular magnetization during reversal. [ABSTRACT FROM AUTHOR]

FexNi1-xF2 is an antiferromagnet with a magnetic anisotropy that can be varied continuously by changing the concentration x. In studying the exchange bias of a polycrystalline Co grown on FexNi1-xF2 (110) epitaxial films, a giant uncompensated magnetization, of up to 16% of the Co magnetization, was observed in the hysteresis loops, whose sign was correlated with the sign of the exchange bias field HE. The exchange bias was measured as a function of temperature after cooling the samples in a field of 2 kOe from above the Néel temperature. The uncompensated magnetization had a large coercivity and an exchange bias field HEU of its own. The uncompensated magnetization of the x=0.05 and x=0.21 samples had a negative HEU while that of the x=0.49 sample was positive. The uncompensated magnetization could be reversed by applying a large field at low temperatures, which also reversed the sign of the exchange bias. [ABSTRACT FROM AUTHOR]

Through detailed measurements of the exchange-bias behavior, we have demonstrated that an antiferromagnetic interfacial exchange coupling exists in epitaxial bilayers of the two ferromagnets La0.67Sr0.33MnO3 and SrRuO3. The bilayers were grown on SrTiO3 substrates by pulsed laser deposition with atomic layer control. By field cooling, or by applying a low-temperature pinning field, the bilayers exhibit exchange bias, with the magnetization loops shifted from zero field by the exchange field HE. In the case of field cooling, we find that both the magnitude and sign of exchange field depend on cooling field, consistent with antiferromagnetic interfacial exchange. The coercivity is maximum near the cooling fields that produce zero exchange field. [ABSTRACT FROM AUTHOR]

Stack giant magnetostrictive actuators (SGMAs) are widely used in various fields for its merits such as saving the space and improving the evenness of the bias magnetic field provided for the giant magnetostrictive material (GMM). In this paper, based on the flow path of the magnetic flux in SGMA, a magnetic equivalent network corresponding to quasistatic conditions is proposed taking flux leakage and fringing effect into account. Meanwhile, complex reluctances of the GMM rods are introduced to describe the decrease and phase shift of magnetic field intensities caused by eddy current under high-frequency excitation signals. Furthermore, the magnetic equivalent network, determining the relationship between excitation signals and magnetic field intensities, is combined with the Jiles–Atherton model, nonlinear constitutive theory of GMM concerning multi-field coupling, and structural dynamics of SGMA so as to derive a multi-field coupling model predicting the tracking behaviors of SGMA to the excitation signals. Moreover, a finite element method is conducted, an SGMA prototype is fabricated, and an experimental platform is set up to verify the proposed model. Comparison between results derived from the magnetic equivalent network and those calculated by the finite element method indicates that the proposed network is able to predict the magnetic field distribution inside the SGMA prototype in quasistatic conditions; further comparison between results obtained from the proposed multi-field coupling model and those from experiments indicates that the model can accurately predict tracking behaviors of the SGMA prototype to the excitation signals. [ABSTRACT FROM AUTHOR]

The effect of antiferromagnetic (AFM) layer on exchange bias (EB), training effect, and magnetotransport properties in ferromagnetic (FM) /AFM nanoscale antidot arrays and sheet films Ag(10 nm)/Co(8 nm)/NiO(tNiO)/Ag(5 nm) at 10K is studied. The AFM layer thickness dependence of the EB field shows a peak at tNiO=2 nm that is explained by using the random field model. The misalignment of magnetic moments in the three-dimensional antidot arrays causes smaller decrease of EB field compared with that in the sheet films for training effect. The anomalous magnetotransport properties, in particular positive magnetoresistance (MR) for antidot arrays but negative MR for sheet films are found. The training effect and magnetotransport properties are strongly affected by the three-dimensional spin-alignment effects in the antidot arrays. VC 2014 AIP Publishing LLC. [ABSTRACT FROM AUTHOR]

The influence of antiferromagnetic (AF) thickness on static and dynamic magnetic properties and their thermal stability in NiFe/FeMn multilayered thin films was investigated systematically. It was found that dynamic magnetic anisotropy rises at the AF thickness lower than that of static magnetic anisotropy and exchange bias. This behavior is suggested to be due to the contribution of rotatable anisotropy arising from time-dependent rotatable part of the AF spins. It is also due to the contribution of rotatable anisotropy and exchange bias that makes the thermal stability of static and dynamic anisotropies varied with AF thickness. The temperature dependences of ferromagnetic resonance frequency, Gilbert damping factor and frequency linewidth dependent on AF thickness are also discussed in conjunction with the variations of the dynamic anisotropy and exchange bias field to provide a comprehensive picture of the physical origin of their thermal stability. [ABSTRACT FROM AUTHOR]

The ferromagnetic resonance (FMR) modes are worked out for the case of exchange coupled bilayer thin films where the anisotropy axis in the ferromagnetic film is tilted out of the plane. General formulas are obtained for the mode position, frequency and field linewidths, and intensity for an arbitrary tilt angle. The analysis is then applied for the in-plane, weak and strong perpendicular anisotropies. Analytical expressions for the magnetization curve and the FMR modes are derived. It will be shown how the exchange anisotropy field HE, the uniaxial anisotropy HK, and the magnetization angle are related to the FMR spectrum characteristics and how they can be found in a straightforward manner. [ABSTRACT FROM AUTHOR]

Strong enhancement of exchange bias (EB) effect in phase-separated CaMn0.9Ru0.1O3 manganite with ferromagnetic phase heavily suppressed under pressure was observed in the measurements of field-cooled magnetization hysteresis loop. It was found that both EB field HE and normalized remanence asymmetry pronouncedly increase with increasing pressure P, enlarging by one order of magnitude at P = 10 kbar. In contrast, the coercive field HC shows a non-monotonic variation with pressure, reaching a maximum value at around 5 kbar. Such unusual HC(P) dependence may be explained by transformation from multi-domain to single-domain state in a system of ferromagnetic (FM) size-variable particles. Comparison of HE(P) with HC(P) data indicates remarkable enhancement of EB with decrease in HC in the pressure range between 5 and 10 kbar. It is argued that a strong increase of HE under pressure is attributed to the suppression of FM phase, i.e., to the decrease in size of FM clusters embedded in antiferromagnetic matrix. Presented results show that the EB effect can be tuned in a wide range by external pressure. [ABSTRACT FROM AUTHOR]

Polycrystalline Fe0.4Mn0.6 layers with the different thickness are deposited on 4-nm-thick single-crystalline Co2FeAl layers, which are grown on GaAs (001) substrates at room temperature by molecular-beam epitaxy. Both the exchange bias and the in-plane magnetic anisotropies of the bilayers are strongly dependent on the thickness of the Fe0.4Mn0.6 layer. The former is described using a granular level model. A modified Stoner-Wohlfarth model is used to explain the in-plane magnetic anisotropies observed at 5 K, while one possible reason for the magnetic anisotropies measured at 300 K is the complex interfacial magnetic properties proved by x-ray magnetic circular dichroism measurements. [ABSTRACT FROM AUTHOR]

The correlation between surface domain structure (SDS) and high frequency magneto-impedance (MI) in amorphous microwires has been systematically studied. First, we applied the magneto-optical polarizing microscopy to determine the SDS and found that it is considerably different in unstressed microwire and in microwires to which tensile and torsional stress were applied. Then, we measured the longitudinal and off-diagonal MI in these microwires and also observed quite different MI dependencies. We analyzed the experimental MI curves and their dependence on the SDS with the help of a simple model that nevertheless yields good qualitative agreement with experiment. We have demonstrated that the analysis of the MI dependencies, especially the off-diagonal one, can reveal the SDS in the microwires. The obtained results can also be useful for magnetic and stress sensing applications. [ABSTRACT FROM AUTHOR]

Ferromagnetic resonance, in 7 to 18 GHz frequency range, is used to investigate a series of rf sputtered Permalloy (Py)/Cu/Co trilayers and Py/Cu/Co/NiO spin valve system. The experimental data, frequency versus applied magnetic field, agree quit well with the theoretical model. The magnetic coupling between Py and Co is found to be ferromagnetic with effective magnetic coupling parameter values increasing from 0.05 to 0.1 erg/cm2 as the interlayer Cu thickness decreases from 10 to 2 nm. While the magnetic coupling leads to a decrease in the resonance fields, HR, of the modes, the exchange anisotropy at the Co/NiO interface shifts the mode upwards. However the shift is more important for the optical mode than for the acoustic one. Hysteresis curves, qualitatively, confirm the ferromagnetic coupling. The antiferromagnetic NiO layer leads to a slight increase in the coercive field. [ABSTRACT FROM AUTHOR]

A nearly free sustained iron film system, deposited on silicone oil surfaces by vapor-phase deposition method, has been fabricated and its crystal structure as well as magnetic properties has been studied. Both the temperature-dependent coercivity Hc(T) and exchange anisotropy field HE(T) of the iron films possess a maximum peak around the critical temperature Tcrit=10–15 and 4 K, respectively. Our experimental results show that the anomalous hysteresis properties mainly result from the oxide surfaces of the films with spin-glass-like phase below freezing temperature Tf=30–50 K. [ABSTRACT FROM AUTHOR]

Presents a study that discussed a transition model and Faraday rotation in ferromagnetic media. Background on the quantum theory of Faraday rotation; Information on the Faraday rotation in different temperature regions; Calculation of the Faraday effect in ferromagnetic media.

We report the observation of a re-entrant spiral (noncollinear) magnetic order and ferroelectricity below 6 K in Mn0.965Fe0.035WO4 under applied magnetic fields above 3.6 T. At zero field, this compound shows a transition into the spiral magnetic and ferroelectric phase at 12 K, and it becomes paraelectric at 10.5 K with the entrance into the commensurate magnetic phase, which is the ground state at H=0. Under magnetic field above 3.6 T, however, the spiral magnetic phases with a larger FE polarization reappears below 6 K. The re-entrant magnetic/ferroelectric phase behavior is further studied by single crystal neutron scattering and the H-T phase diagram is completely resolved from neutron, dielectric constant, polarization, and magnetic measurements. [ABSTRACT FROM AUTHOR]

Unconventional exchange bias (EB) has been studied in CoCr2O4/Cr2O3 nanocomposites, in which the Curie temperature of the ferrimagnetic CoCr2O4 is much lower than the Néel temperature of the antiferromagnetic Cr2O3. A negative EB field of about 2.5 kOe at 5 K is achieved upon cooling in a field of 30 kOe. Meanwhile, the coercivity of the CoCr2O4 nanoparticles has been enhanced significantly by coupling with Cr2O3. The effect of the cooling field on the EB field and coercivity at 10 K has also been investigated. The domain-state model is used to interpret the unconventional EB. Cooling field may play a decisive role in the creation of the interfacial spin configuration for the unconventional EB, not only by exchange interaction between the induced magnetization of a polarized paramagnet and interfacial spins of an antiferromagnet but also by Zeeman interaction between the domain-state surplus magnetization and the external field. [ABSTRACT FROM AUTHOR]

In this paper magnetostrictive rods are analyzed coupling a magnetoelastic model of Terfenol-D rods based on Preisach theory with a finite element electromagnetic field solution, accounting for dynamic effects within the rod. The computed results, compared with experiments, evidence the influence of eddy currents and magnetization dynamic on the magnetostrictive rod behavior. [ABSTRACT FROM AUTHOR]

We investigated long intrinsic Josephson junctions (IJJs) as an oscillator on a Bi2Sr2CaCu2O8+d (Bi-2212) whisker. The oscillator utilizes the effect of flux-flow motion in long IJJs. In-plane areas with the same junction geometry, 15×1.7 μm2 were fabricated by using a three-dimensional focused-ion-beam (FIB) etching method. Those oscillator junctions exhibited uniform multibranch structures and clearly upturned curves under He. The flux-flow velocities (Vff) reached 8.7×105 m/s at 6.2 T and 10 K. We describe the characteristic flux-flow behaviors on long IJJs for high-frequency device applications. [ABSTRACT FROM AUTHOR]

Exchange bias effects have been observed in an array of submicron antiferromagnetic-ferromagnetic dots prepared by nanosphere lithography. The angular dependences of the exchange bias field HE, coercivity HC, and squareness ratio MR/MS of the array of dots have been measured and compared with those of a continuous film prepared under the same conditions. An HE enhancement of around 30% is observed along the field-cooling direction in the dots. The possible mechanisms responsible for this enhancement are discussed. Moreover, magnetic imaging reveals that complex magnetization reversal mechanisms occur in the nanostructures, which cause significant differences in the shape of the hysteresis loops, when compared to the exchange biased continuous films. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have carried out detailed investigations of magnetic ordering and the origin of exchange-bias phenomenology in polycrystalline 154Sm0.4Ca0.6MnO3 perovskite compound by employing dc and ac magnetizations, neutron depolarization, and neutron diffraction techniques. The neutron diffraction study reveals a broad charge ordering transition in the temperature range of 275-150 K, manifested by gradually varying structural distortions. DC magnetization and neutron diffraction studies infer a magnetic ordering around 110 K. Below ~40 K, this compound exhibits a large enhancement of the magnetization and an exchange-bias effect (~18 kOe at 5 K). The exchange-bias effect shows a characteristic temperature and cooling field dependence and a training effect. The compound undergoes a CE-type (checker-board type) antiferromagnetic (AFM) ordering of Mn3+/Mn4+ spins below 110 K. The large magnetization below ~40 K arises from the ferrimagnetic (FIM) ordering of a minority (~5 vol. %) non-perovskite phase of Mn3O4. The appearance of exchange bias is ascribed due to the presence of an interface, formed between the FIM (Mn3O4) phase and the main AFM perovskite phase. Our study has implications in giving new directions in the search of large exchange-bias effects in mixed FIM/AFM bulk systems. [ABSTRACT FROM AUTHOR]

We have studied systematically the effect of field cooling on the magnetic properties of continuous and porous IrMn/[Co/Pd] films. It is found that the coexistence of two ferromagnetic (FM) phases in the porous film, namely, hard-magnetic and soft-magnetic ones, with significantly different magnetic properties relates to the role of pore edges and modifies its magnetic and magnetoresistive properties. It is shown that annealing of the films with their subsequent cooling in an external magnetic field applied for aligning the magnetic moments in the antiferromagnetic (AFM) IrMn layer improves effectively the uniaxial perpendicular anisotropy of the [Co/Pd] layer and induces unidirectional anisotropy in its hard-magnetic regions, blocking simultaneously the soft-magnetic parts by pinning their magnetic moments along the film plane. Magnetoresistance of both continuous and porous films is found to be determined mainly by electron–magnon scattering, whereas the complex morphology of the porous film providing different orientations of exchange coupling at the AFM/FM interface in different film regions modifies significantly the spin-dependent electron transport. The revealed asymmetry of the field dependences of magnetoresistance is attributed both to unidirectional magnetic anisotropy of the FM layer and its splitting into magnetically nonequivalent regions in the porous films. The origin of the observed phenomenon is associated with a local influence on the orientation of AFM magnetic moments by an adjacent ferromagnet. [ABSTRACT FROM AUTHOR]