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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]

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]

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]

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]

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]

Exchange bias in ferromagnetic (F)/antiferromagnetic (AF) bilayers is a function of both the bulk properties of the AF layer and the interfacial properties determining the effective interfacial couplings between the F and AF layers. The distinction between bulk and interface can be clearly revealed in blocking temperature distributions, where AF grain volume distribution results in a high-temperature peak while disordered interfacial magnetic phases produce a low-temperature contribution. However, the coupling conditions producing such bimodal blocking temperature distributions remain to be specified. In this article, we use a granular model which accounts for the disordered interfacial phases by considering small magnetic grains (SGs) with weaker anisotropy and coupling with the F grains at the F/AF interface. The SG are included in the AF material. The coupling conditions producing bimodal blocking temperature distributions were determined. Then, using Monte Carlo simulations, these conditions were validated and the effect of interfacial F-SG coupling on distributions was investigated. We next determined how the ratio between F-SG and F-AF couplings could be used to estimate the surface coverage of the disordered interfacial phases from experimental data. [ABSTRACT FROM AUTHOR]

To study the effect of non-magnetic layer (Cu) on magnetic properties of antiferromagnetic FeMn, multilayers of Ta(5 nm)/[FeMn(t)/Cu(5 nm)]10/Ta(5 nm), where t is varied in the range of 5-15 nm, are fabricated by a combination of RF and DC magnetron sputter deposition. Magnetization curves for these samples exhibit magnetic hysteresis, and when the samples are cooled in an applied magnetic field, the hysteresis loops are shifted. This shift is attributed to an 'intrinsic' exchange bias effect (i.e., it is observed without a separate ferromagnetic layer). Presented temperature and thickness dependences of the coercive field, magnetic moment, and exchange bias field provide insights into the origin and mechanism of the observed intrinsic exchange bias. [ABSTRACT FROM AUTHOR]

We establish a simple ferromagnetic/antiferromagnetic/ferromagnetic trilayer model, where the lower-interface coupling is varied and study its combined effect with cooling field or temperature on the upper-interface exchange bias effect. Exchange bias field is almost independent of cooling field, if the lower-interface coupling is ferromagnetic and large. Otherwise, its value becomes sensitive to cooling field, and the evolution trend of exchange bias with increasing cooling field depends on the sign and strength of lower-interface coupling. On the other hand, the blocking temperature, below which exchange bias emerges, is reduced (or elevated) in the trilayers with a large ferromagnetic (or antiferromagnetic) lower-interface coupling. The numerical results obtained are interpreted well in terms of the magnetization behaviors in the respective layers. A cooling field creates a low-temperature frozen configuration in the antiferromagnetic layer after cooling to generate exchange bias, while such a configuration related to exchange bias and blocking temperature may be rearranged due to existence of the second ferromagnetic layer on the backside of the antiferromagnetic layer. This work provides an insight into the exchange bias effect and its propagation in such a trilayer stack employing a rather thin antiferromagnetic layer. [ABSTRACT FROM AUTHOR]

A systematic study of the effect of ferromagnetic thickness on magnetic and microwave properties of exchange-biased NiFe/FeMn multilayered thin films was carried out with regards to thermal stability. The temperature-dependent microwave characteristics of the films were obtained from the near-field microwave microscopy technique and analysed based on Landau-Lifshitz-Gilbert equation. The complex microwave permeability spectra of the magnetic thin films up to 5 GHz in the temperature range from room temperature to 420 K were measured. It was found that thicker ferromagnetic layers helped to reduce the dependence of the magnetic properties on temperature, leading to better thermal stability. The saturation magnetization MS, dynamic magnetic anisotropy field HKdyn, and ferromagnetic resonance frequency fFMR were found to decrease with temperature, while the effective damping coefficient αeff was increased with temperature. We also investigate the rotational magnetic anisotropy field HKrot with temperature which gives a measure of the rotatable magnetization of the antiferromagnetic layers and its thermal stability. [ABSTRACT FROM AUTHOR]

In an antiferromagnetic (core)/ferromagnetic (shell) nanoparticle, the transition behaviors from negative (NEB) to positive exchange bias (PEB) at low temperature after field cooling are studied in detail. The NEB field may exhibit an oscillatory behavior due to the competition between interfacial coupling and cooling field. The critical cooling fields, at which the transitions occur, exhibit a logarithmic decrement with the decrease of interfacial coupling, but indicate a linear decrease with the decrease of antiferromagnetic coupling or with the further dilution in the antiferromagnetic core. With the further increase of cooling field, the PEB field increases linearly and finally levels off. Moreover, the weaker antiferromagnetic coupling may enhance the NEB field value, whereas the suppression of PEB may be observed by diluting the antiferromagnetic core. The magnetization reversal by coherent rotation strongly depends on the variation of the magnetic parameters, because its occurrence just needs to consume a lower additional energy, which is the main reason for these unique phenomena. We have shed new light on the microscopic origin of the peculiar magnetic properties in the nanoparticles with such an inverted magnetic structure. [ABSTRACT FROM AUTHOR]

Structural and magnetic measurements were done on polycrystalline manganite, Pr0.5 Eu0.5 MnO3. The Rietveld refinement of the x-ray powder diffraction pattern at room temperature suggests considerable Jahn-Teller distortion due to ionic size mismatch of the isovalent ions. Dc and ac magnetometry suggest a disordered antiferromagnetic (AFM) state, exhibiting glassy magnetic behavior at low temperature. Cooling in a static magnetic field reveals a considerable shift of the magnetic hysteresis loops, a typical manifestation of exchange bias. Interestingly, we observe the absence of training effect in exchange bias. The temperature, cooling field dependent study of exchange bias, and absence of exchange bias in La0.5 Eu0.5 MnO3 suggest a novel low temperature phase separation between a disordered AFM phase induced by the Mn moments and another highly anisotropic phase involving ordering related to the rare-earth moments. It appears that this unique magnetic ground state exhibiting exchange bias is a consequence of the structural distortion inherent in the system. [ABSTRACT FROM AUTHOR]

A modified Monte Carlo method using the Metropolis algorithm is performed to simulate the hysteresis behaviors of the nanoparticles with an inverted antiferromagnetic (core)/ferromagnetic (shell) morphology at low temperature after field cooling. We have examined the dependence of exchange bias on the hard ferromagnetic surface anisotropy and the training effect. Our simulations reveal that, besides the antiferromagnetic core, another pinning source, namely, the hard ferromagnetic surface, can also contribute to the exchange bias in such a special structure. Above a critical surface anisotropy, the exchange bias field has a steep increase by means of the change of the magnetization reversal mechanisms, which are affected by the surface anisotropy. During the consecutive hysteresis loops, the exchange bias field decreases gradually to a constant value. The phenomena have been interpreted well by considering the combination of locking, releasing, and stabilizing of the spins on the antiferromagnetic core surface and the energy competition between Zeeman and antiferromagnetic anisotropy. Our results are in good agreement with the experimental findings. [ABSTRACT FROM AUTHOR]

In an external magnetic field, the band structure of a two-dimensional photonic crystal (PC) composed of parallel antiferromagnetic cylinders in a background dielectric is investigated with a Green's function method. The cylinders with two resonant frequencies form a square lattice and are characterized by a magnetic permeability tensor. In our numerical calculation, we find that this method allows fast convergence and is available in both the resonant and non-resonant frequency ranges. In the non-resonant range, the PC is similar in band structure to an ordinary dielectric PC. Two electromagnetic band gaps, however, appear in the resonant frequency region, and their frequency positions and widths are governed by the external field. The dependence of the electromagnetic gaps on the cylinder radius also is discussed. [ABSTRACT FROM AUTHOR]

In-plane exchange bias (EB) in [Pt/Co]n/NiFe/NiO heterostructures with orthogonal easy axes is investigated. The reversible in-plane EB effect at the ferromagnetic (FM)/FM [Pt/Co]n/NiFe interface allows one to manipulate the value and direction of the EB of the heterostructures, which can be induced by applying a magnetic field larger than the perpendicular anisotropy field of the [Pt/Co]n multilayers. The difference between the EB of the heterostructures after field cooling and zero field cooling disappears at 120 K, which may originate from the exchange coupling at the FM/antiferromagnetic (AFM) NiFe/NiO interface. The NiFe thickness dependence of the bias field of the EB exhibits behavior similar to that in conventional FM/AFM bilayers. The EB can be maintained even at room temperature. [ABSTRACT FROM AUTHOR]

The angular dependence of asymmetric magnetization reversal in exchange biased NiO/Ni bilayers was investigated using a vectorial vibrating sample magnetometer. Different angular dependences of the exchange field, coercivity, and asymmetry were obtained by tuning the NiO layer thickness (tNiO). Comparing the experimental data with the theoretical calculations, we found that the asymmetric magnetization reversal of bilayers with larger tNiO was dominated by competing uniaxial and unidirectional anisotropies, and an additional rotatable anisotropy was required in the simulation to correctly describe the magnetization reversal of bilayers with smaller tNiO. The irreversible magnetization switches of a large amount of antiferromagnetic grains in thin NiO layers are responsible for the rotatable anisotropy, which may also significantly affect the shape of the hysteresis loops and the range of angles with symmetric magnetization reversal. [ABSTRACT FROM AUTHOR]

In the framework of models that assume planar domain wall formed at the antiferromagnetic part of the interface of exchange-biased bilayers, one cannot distinguish between the cases of high or low ratios between the coupling and the antiferromagnet’s anisotropy fields by using hysteresis loop measurement, ferromagnetic resonance, anisotropic magnetoresistance, or ac susceptibility techniques applied on one and the same sample. The analysis of the experimental data obtained on a series of FeMn/Co films indicated that once the biasing is established the variation in the coercivity with the FeMn layer thickness could be essential for solving this problem. If the coercivity decreases with the thickness then the interlayer exchange coupling is the parameter that varies while the domain-wall energy of the antiferromagnet remains practically constant. [ABSTRACT FROM AUTHOR]

For NiFe/FeMn bilayers, the correlation among the exchange field, the coercivity, the training effect, the hysteretic effect of the angular dependence of the exchange bias, and the rotational hysteresis loss has been studied as a function of the antiferromagnet layer thickness tAFM. With increasing tAFM, all these quantities undergo nonmonotonic variations, except for the monotonic change in the exchange field. The maximal values of the coercivity, its relative change, and the rotational hysteresis loss are almost located at the same tAFM of 3.8 nm. The maximal values of the relative change in the exchange field and of the hysteretic effect of the angular dependence are located at 2.5 and 3.0 nm, respectively. The rotational hysteresis loss and the hysteretic behavior of the angular dependence of the exchange bias have different characteristics. The variations of all physical quantities with tAFM can be ascribed to the irreversible reversal of the antiferromagnet spins, which are governed by the Arrhenius–Néel law, except for that of the rotational hysteresis loss. [ABSTRACT FROM AUTHOR]

A sinusoidal field solution for a nonlinear transverse magnetic surface wave in a symmetric planar transmission line made of a superconducting film and two antiferromagnets is derived. This solution enables us to investigate the propagation characteristics in the infrared frequency region. Propagation characteristics such as the attenuation constant and the phase constant are numerically analyzed as a function of the frequency, the temperature, and the thickness of a superconductor as well. In the temperature-dependent attenuation constant, it is found that there exists a characteristic temperature at which the attenuation constant attains a maximum. This characteristic temperature decreases with increasing frequency. In addition, it is seen that both the attenuation constant and the phase constant decrease with increasing thickness of a superconducting film. Finally, numerical result in the total power flow reveals that there exists a cutoff propagation constant. Electromagnetic wave can propagate through the line when the propagation constant is greater than this cutoff value. [ABSTRACT FROM AUTHOR]

Perpendicular exchange bias can be established in ferromagnetic/antiferromagnetic multilayers with intrinsic in-plane shape anisotropy through out-of-plane field cooling. The induced anisotropy along the hard axis possesses the same interfacial nature as that after the conventional in-plane field cooling. While the in-plane angular dependence of longitudinal exchange bias can be well described by the uniaxial coherent rotation model, out-of-plane measurements show totally different angular dependent hysteretic behaviors for both longitudinal and perpendicular exchange biases. After taking into account the competitive field cooling induced anisotropy, the thin film shape anisotropy, the three-dimensional coherent rotation model alone can quantitatively explain the observed out-of-plane angular dependent magnetization reversal for both field cooling geometries. Magnetization reversal is found to be accomplished by coherent rotation out of the plane determined by anisotropic axis and applied field. The model is also applicable in predicting the more general thin-film magnetization reversal with out-of-plane applied fields. [ABSTRACT FROM AUTHOR]

A series of Ni(1-x)FexO (x=0, 0.015, 0.03, 0.05, and 0.1) bulk samples was synthesized by the chemical concentration-precipitation method. Phase composition analysis was carried out, which showed that trace amounts of ferromagnetic phase NiFe2O4 could not be detected by x-ray diffraction in these bulk samples with x≤0.03. When x>0.03, NiFe2O4 ferrite is detected easily. The magnetic properties of all the bulk samples were investigated by measuring their magnetization as a function of temperature and magnetic field. The results indicated that all the bulk samples sintered in air exhibited large room-temperature ferromagnetic behavior ascribed to a ferromagnetic impurity phase. Simultaneously, an exchange bias and training effect were also observed in all the bulk samples, suggesting the possibility of the existence of a strong ferromagnetic/antiferromagnetic exchange coupling in this kind of compound. Specifically, the exchange bias field could be tuned by changing the concentration of the Fe dopant. [ABSTRACT FROM AUTHOR]

Influence of (Ni81Fe19)100-xCrx seed layer on structure and magnetic properties of NiFe/PtMn bilayers was systemically investigated by magnetic measurements and x-ray diffraction. The results indicated that the pinning field Hex of NiFe/PtMn bilayers has a strong correlation with the Cr content of (Ni81Fe19)100-xCrx seed layer, which can effectively influence grain size, crystal texture, and L10 ordering phase transformation of PtMn. When the Cr content is 40%, PtMn shows strong (111) texture and large grain size, but the L10 ordering phase transformation is weak after annealing, which resulting in a low pinning field Hex. When the Cr content is 34% and 50%, PtMn has weak (111) texture and small grain size, but these are in favor of the L10 ordering phase transformation after annealing, resulting in a high pinning field Hex. [ABSTRACT FROM AUTHOR]

An experimental study on the exchange bias properties of bulk polycrystalline Ni50Mn50-xSnx Heusler alloys has been performed. Martensitic transformations have been observed in the alloys for some critical Sn concentrations. The alloys, while in their respective martensitic phases, are found to exhibit exchange bias effect. Shifts in hysteresis loops of up to 225 Oe were observed in the 50 kOe field cooled samples. The observed exchange bias behavior in Ni50Mn50-xSnx is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions in the system. [ABSTRACT FROM AUTHOR]

We report on the investigation of the exchange bias effect in Fe layers on EuTe(111), an antiferromagnetic semiconductor. For this ferromagnet (FM)/semiconducting antiferromagnet (AFM) exchange bias system, we have found positive and negative exchange bias effect (EB). Fresh samples exhibit positive EB, independently of the applied cooling field, indicating antiferromagnetic coupling between the FM and the AFM layers at the Fe/EuTe(111) interface. The change in EB with time, from positive EB for fresh samples to negative EB after short time,is attributed to aging effects at the Fe/EuTe interface. [ABSTRACT FROM AUTHOR]

We study the performance of a high frequency band stop filter which can work in both the microwave and infrared regions using an antiferromagnet film as the active material. We find that the band stop frequencies can be adjusted by changing the applied magnetic field or by changing the temperature. Also, the attenuation of the wave at a band stop frequency can be controlled by varying the physical parameters such as the thickness of the antiferromagnetic film or the thickness of the dielectric spacer. In addition, the attenuation is strongly dependent on the anisotropy field in the antiferromagnet. Further, the band stop filter using antiferromagnet does not have the constraints due to skin depth and conductivity losses as many of the antiferromagnets are insulators. [ABSTRACT FROM AUTHOR]

We study the ferromagnetic resonance (FMR) on a system consisting of a ferromagnetic (FM) film and an antiferromagnetic film. The FMR frequency and its linewidth were derived analytically and calculated numerically as a function of applied magnetic field and its angle, exchange anisotropy, strength, and angle of the stress anisotropy for single crystal FM films with, respectively, uniaxial or cubic magnetocrystalline anisotropies. The results show that the system with an applied or residual stress anisotropy has some symmetrical, or equivalent, directions of the hard and easy axes. This property is always destroyed by the asymmetrical shift caused by the exchange anisotropy. This fact will be helpful to the experimentalist in distinguishing between the stress and the exchange anisotropies. [ABSTRACT FROM AUTHOR]

Louis Néel (1904-2000) was probably the most influential figure in applied magnetism in the 20th century. He pioneered or developed concepts such as antiferromagnetism, ferrimagnetism, superparamagnetism, magnetic viscosity, surface and induced anisotropy, domain walls, orange-peel coupling, and exchange anisotropy, many of which are of great importance in modern thin-film devices. A brief summary is given of his career and scientific contributions. [ABSTRACT FROM AUTHOR]

A new, simple method is presented for the preparation of thin Co/CoO bilayers exhibiting considerably improved characteristics of the magnetic behavior and large exchange bias effects. The ultrathin antiferromagnetic layer is formed at room temperature by controlled in situ exposure of a clean metal layer to pure oxygen gas. The exposure amounts only 100-10 000 L at an oxygen pressure of 10[sup -5] mbar. High purity gases can be used. This method allows to maintain optimum ultrahigh vacuum conditions in the preparation chamber which is an indispensable condition for the preparation of complex layer systems. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which observed a strong interlayer exchange interaction in polycrystalline antiferromagnetic cobalt oxide (CoO)-nickel oxide (NiO) thin film superlattices. Production of CoO-NiO superlattices and CoO-NiO bilayers; Differences in the properties exhibited as-deposited and after field cooling; Ways in which exchange anisotropy can affect the hysteresis loop of the ferromagnet.

The angular distribution of exchange bias and its size dependence have been studied in MgO magnetic tunnel junctions with IrMn antiferromagnetic pinning layer. Device size was in the mesoscopic range where the finite number of antiferromagnet grains determines the statistical properties of exchange bias. These properties are not consistent with models of the antiferromagnet breaking into domains but are consistent with Fulcomer and Charap [J. Appl. Phys. 43, 4190 (1972)] of independent antiferromagnet grains. [ABSTRACT FROM AUTHOR]

A systematic investigation of structural and magnetic properties of FePt/FeRh bilayers has been carried out. The transition temperature of single FeRh layer is higher than that of FePt/FeRh bilayer. A sharp decrease in coercivity is observed at transition temperature for FePt/FeRh bilayer. The thickness FePt dependence of exchange bias field and unidirectional anisotropy constant are discussed. Of interest is the exchange bias effect that appears in FePt/FeRh bilayer and the unidirectional anisotropy constant, which is very large (up to 0.8 erg/cm2), suggesting that this system can be applied for spin-valve sensors and heat assisted magnetic recording medium. It may also provide some useful information for better understanding of the mechanism of exchange bias. [ABSTRACT FROM AUTHOR]

Exchange biaslike phenomenon is observed in the Zn doped spinel polycrystalline CuCr2O4. The magnetic hysteresis loop shifts in both horizontal and vertical directions at 5 K after the samples are cooled down to 5 K in a magnetic field. The nature of this magnetic anisotropy arises from the freezing properties of the local anisotropy in the cluster glass system. The magnetic shifts along both directions can be observed directly under the principle that the spins of a cluster are frozen in random orientations upon zero field, and aligned to the field direction upon field cooling. [ABSTRACT FROM AUTHOR]

The training effect of the so-called exchange bias in coupled polycrystalline NiFe/IrMn thin films has been experimentally and theoretically investigated. A different formula is used to describe the exchange bias dependence on the measurement cycle number. It can be understood to be a consequence of the antiferromagnetic domain dynamics based on the Kolmogorov-Avrami [Izv. Akad. Nauk, Ser. Math. 3, 355 (1937); J. Chem. Phys. 8, 212 (1940)] model, which describes the nucleation and growth of antiferromagnetic domains in the film structures. [ABSTRACT FROM AUTHOR]

We investigated theoretically the magnetization reversal via vortex nucleation and annihilation in double-layer ferromagnetic/antiferromagnetic cylindrical dots. The influence of the antiferromagnetic layer on the magnetization reversal is accounted for by means of an interfacial, unidirectional exchange field. We consider explicitly a nonuniformity of the magnetization reversal mode along the direction perpendicular to the layers, which gives rise to a nonuniform Bloch line. The vortex annihilation fields, the vortex trajectory, and the average dot magnetization are calculated as functions of the dot geometrical parameters and the external field direction with respect to the exchange-bias field. The calculations are compared with recent experiments. [ABSTRACT FROM AUTHOR]

We have studied the magnetic stability in exchange-bias and exchange-spring systems during repeated reversal of the pinned layer. The samples were prepared by epitaxial sputter deposition. The exchange-biased system consists of a combination of ferromagnetic and antiferromagnetic Fe/Cr superlattices. The exchange-spring system is a bilayer structure made of hard Sm-Co and soft Fe ferromagnetic layers. The magnetic properties were investigated using the magneto-optic Kerr effect during repeated reversal of the soft layer magnetization by field cycling up to 10[sup 7] times. The experimentally observed decay behaviors are discussed in terms of microstructure and spin configuration of the pinning layers. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The exchange bias effect is known to depend strongly on the condition of the ferromagnet/antiferromagnet interface. Bilayers of single-crystal Fe and polycrystalline KNiF[sub 3] were grown and exchange bias observed using superconducting quantum interference device magnetometry. Hysteresis loops after field cooling are asymmetric in the forward and reverse directions. This asymmetry disappears at 50 K, indicating a blocking temperature for the bias well below the Néel temperature of KNiF[sub 3] (250 K). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study that examined nickel-oxygen (NiO)/nickel-iron (NiFe) bilayer thin films. Use of radio frequency reactive and direct current magnetron sputtering; Investigation of the exchange coupling strength between NiO and NiFe as a function of NiO texture and interface roughness; Background on the antiferromagnetic and ferromagnetic thin films.

Presents a study which examined nuclear spin relaxation in S=1 Heisenberg antiferromagnetic chains in high magnetic field. Effect of an external magnetic field on the photon spin-lattice relaxation time on two compounds; Numerical methods; Results.

Examines the influence of isolated magnetic impurities or defects on the spin-wave spectrum of semi-infinite ferromagnets and antiferromagnets. Use of Green's-function theory and Heisenberg model; Ways to obtain the spin-wave modes and spin correlations of a semi-infinite system with a defect; Analogous calculations for the case of semi-infinite rutile-structure antiferromagnets.

We perform a theoretical study of the reflection of infra-red radiation from antiferromagnets and M-type barium hexagonal ferrite using an attenuated total reflection (ATR) geometry. At an arbitrary angle of propagation, the electromagnetic waves in the magnetic materials cannot be separated into the usual pure transverse electric (TE) and pure transverse magnetic (TM) modes. We develop a method to solve for the ATR reflection for arbitrary angles of propagation. Using reflection maps, one can determine the dispersion relations for both bulk and surface polaritons. We find that surface polariton features in the reflection map are present at all angles for both incident TE and TM polarizations, with the exception of TM polarization when the plane of incidence is perpendicular to the applied magnetic field. We also see that the interaction of the incident electromagnetic wave with surface polaritons can cause significant transfer from TE to TM modes (and vice versa) upon reflection. When the surface modes vanish, we see that the remaining bulk mode displays reciprocal behavior. [ABSTRACT FROM AUTHOR]

The phenomenon of exchange bias training effect is successfully obtained by introducing an out-of-step of energy dissipation of ferromagnet and antiferromagnet. The numerical results suggest that the energy dissipation pattern of the antiferromagnet plays a crucial role for the understanding of the exchange bias training effects, e.g., when the energy dissipation pattern of the antiferromagnet follows power-law function, the best fit function for the dependence of exchange bias on the cycle number is power-law. The physical mechanism that the amount of the coercive field shift in the descent branch is larger than that of ascent branch for the hysteresis loop measurement and the coercivity of ferromagnet/antiferromagnet bilayers is always larger than that of the corresponding ferromagnet layer has been illuminated, respectively. Moreover, under the different values of damping parameter, the anomalous training effect observed by recent experiment [Z. Shi et al., Appl. Phys. Lett. 93, 222504 (2008)] and the conventional training effect can also be elucidated, respectively. [ABSTRACT FROM AUTHOR]

A comprehensive experimental study of the effect of antiferromagnetic (AF) dilution on the magnetic properties and microwave characteristics of Fe70Co30/(Mn75Ir25)1-x(Al2O3)x multilayered thin films with the variation of AF thickness was performed. Our result reveals a linear relationship between the critical AF thickness and the dilution of the AF layers providing an evidence of a volume effect in the AF layers consistent with the domain state model. The AF magnetic anisotropy deduced from the critical AF thickness was found to reduce monotonically with the AF dilution. The variations of exchange bias, rotational magnetic anisotropy, ferromagnetic resonance frequency, and effective damping factor with the AF dilution and thickness have also been presented and discussed. [ABSTRACT FROM AUTHOR]

Ni50Mn37Sn13 ribbons were produced by the melt-spinning method. Structure and magnetic measurements on the Ni50Mn37Sn13 ribbons indicated that it is ferromagnetic below 340 K and undergoes an austenitic-to-martensitic phase transition just below room temperature. The austenitic phase has the cubic L21 structure, with the excess manganese atoms occupying the 4(b) sites. The martensitic phase has an orthorhombic structure. With increasing applied magnetic field, the martensite start temperature Ms and martensite finish temperature Mf shift to lower temperatures because of the field-induced phase transition. The exchange-bias effect is observed and strongly varied with different cooling fields at low temperature. At 5 K, the exchange-bias field reaches a maximum of 290 Oe when the cooling field increases to 200 Oe, and then reduces sluggishly with further increase of the cooling field because of weakening of exchange coupling between antiferromagnetic and ferromagnetic interfaces. [ABSTRACT FROM AUTHOR]