In conventional exchange-bias system comprising of a bilayer film of ferromagnet (FM) and antiferromagnet (AFM), investigating the role of spin-disorder and spin-frustration inside the AFM and at the interface has been crucial in understanding the fundamental mechanism controlling the exchange-bias -- an effect that leads to a horizontal shift in the magnetization hysteresis response of the FM. Similarly, in the recently reported monolayer molecular exchange-bias effect requiring no AFM layer, probing magnetic-disorder at the FM/molecule interface or inside the FM layer can provide new insights into the origin of molecular exchange-bias and the associated physics. In this article, by cooling the Fe/metal-phthalocyanine devices in oscillating magnetic field, we demonstrate a characteristic temperature dependent response of exchange-bias shift and ferromagnet coercivity that is supportive of a spin-glass behavior. Here, the origin of spin-glass is attributed to the spin frustration created in the magnetic structure of the Fe layer, which was absent in our reference-Fe studies. These results highlight the strong influence of FM/molecule interface pi-d hybridization on the magnetic exchange interactions extending deeper into the FM layer.
Exchange bias in ferromagnetic/antiferromagnetic systems can be explained in terms of various interfacial phenomena. Among these spin glass frustration can affect the magnetic properties in exchange bias systems. Here we have studied a NiMn/CoFeB exchange bias system in which spin glass frustration seems to play a crucial role. In order to account the effect of spin glass frustration on magnetic properties, we have performed the temperature and cooling field dependence of exchange bias. We have observed the decrease of exchange bias field (HEB) with cooling field (HFC) whereas there is not sig…
The mass average interdiffusion coefficient DM is an approximated constant value of the interdiffusion coefficient which is relevant in the kinetics of ion exchange in silicate glasses. In this study, it is presented a simple technique for its determination based on the weight change of a glass sample after ion exchange. The theoretical basis of the method is presented in detail together with the approximations assumed in considering the constancy of the DM . Experimental results are presented for soda-lime silicate glasses and it is demonstrated the correlation of DM with the ion exchange tem…
We have performed magnetic measurements like temperature (T), cooling field (HFC) dependence of exchange bias (EB) and training effect to investigate the magnetic nature of the interface of the Fe/Ir20Mn80 systems. Thin film bilayer samples of different thicknesses of Ir20Mn80 have been prepared by dc magnetron sputtering at room temperature. The variation of exchange bias field (HEB) with the increase in thickness of Ir20Mn80 predicts the antiferromagnet (AFM) bulk spins contribution to EB. Exponential decay of HEB and coercive field (HC) with temperature reveals the presence of spin glass (S…
The zero-field-cooled exchange bias (ZEB) effect is a remarkable phenomenon recently reported for some reentrant spin glass-like compounds. In this work, the time-evolution of magnetization is thoroughly investigated for two ZEB materials in order to figure out the role played by the spin glass-like phase on such effect. La$_{1.5}$Sr$_{0.5}$CoMnO$_{6}$ and La$_{1.5}$Ca$_{0.5}$CoMnO$_{6}$ were chosen as representative samples of ZEB systems, since the former compound presents the largest ZEB reported so far, while the second has a much smaller effect, despite being structurally/chemically simil…
The present study reports Al induced crystallization (AIC) of amorphous (a)-SiGe in Al-Ge-Si ternary system at low temperature ~ 350 degree C. In addition to crystallization, the isothermal annealing of a-SiGe/AlOx/Al/corning-glass (CG) structure was found to be accompanied by an Al induced layer exchange (ALILE) phenomenon. The evolution of residual stress in the Al layer during isothermal annealing is evaluated using X-ray diffraction based technique to ascertain the role of stress in the ALILE process. A corroboration of the stress with the growth kinetics, analyzed using Avrami theory of p…
Zero field cooled spontaneous exchange bias (SEB) is observed in epitaxial La0.7Sr0.3MnO3 (LSMO):NiO self-assembled nanocomposite thin films grown on (001) SrTiO3 single crystal substrate by pulsed laser deposition. SEB is displayed by the novel asymmetry in the hysteresis loop of the composite film along with the field cooled conventional exchange bias (CEB) effect. The training effect shows that exchange bias relaxation is disorder mediated. It is revealed from DC magnetization results that such nanocomposite film divulges spin glass like behaviour, which is arising due to competing ferromag…
Ion-exchange is commonly used to chemically strengthen glasses, by replacing small atoms by larger ones at sub T$_g$ temperature, thereby inducing a compressive stress. However, the resulting expansion of the glass remains lower than that predicted by the difference of molar volumes of the as-cooled glasses, an anomaly that remains poorly understood. Here, based on molecular dynamcis simulations of permanently densified sodium silicate glasses coupled with topological constraint theory, we show that the rigidity of the network controls the extent of the dilatation. Isostatic networks, which ar…
Here, we investigated the influence of grain formation on the magnetization reversal of SmCo5/Co at low temperature. A set of SmCo5/Co bi-layer samples were fabricated under identical conditions on MgO(100) and glass substrates with a Cr underlayer. Analysis of each magnetic layer by an Atomic Force Microscope (AFM) reveals that MgO(100) results small and uniform grain formation of 23 nm in contrast to 57 nm on glass, and x-ray diffraction studies show that the sample on MgO(100) has high crystallinity with SmCo5(11 0) phase. At room temperature, both samples exhibit good hard magnetic propert…
We observe an enormous $\textit{spontaneous}$ exchange bias ($\sim$300-600 Oe) - measured in an unmagnetized state following zero-field cooling - in a nanocomposite of BiFeO$_3$ ($\sim$94%)-Bi$_2$Fe$_4$O$_9$ ($\sim$6%) over a temperature range 5-300 K. Depending on the path followed in tracing the hysteresis loop - positive (p) or negative (n) - as well as the maximum field applied, the exchange bias ($H_E$) varies significantly with $\mid-H_{Ep}\mid$ $>$ $\mid H_{En}\mid$. The temperature dependence of $H_E$ is nonmonotonic. It increases, initially, till $\sim$150 K and then decreases as the …
In a paper submitted to the Arxive some time ago (cond-mat/0509270), R. S. Fishman et al. considered double-exchange model on a Bethe lattice in infinite dimensions using dynamical mean-field theory. We present a somewhat different derivation of their general formula for the magnetic disorder - order transition temperature and comment on the interpretation of the intermediate (between ferromagnetism and antiferromagnetism) phase obtained by the authors.
The phenomenology of exchange bias effects observed in structurally single-phase alloys and compounds but composed of a variety of coexisting magnetic phases such as ferromagnetic, antiferromagnetic, ferrimagnetic, spin-glass, cluster-glass and disordered magnetic states are reviewed. The investigations on exchange bias effects are discussed in diverse types of alloys and compounds where qualitative and quantitative aspects of magnetism are focused based on macroscopic experimental tools such as magnetization and magnetoresistance measurements. Here, we focus on improvement of fundamental issu…
We report a giant zero field cooled exchange bias (ZEB) effect (~0.65 T) in La1.5Sr0.5CoMnO6 sample. Magnetic study has revealed a reentrant spin glass ~90 K, phase separation to spin glass and ferromagnetic phases below 50 K and canted antiferromagnetic transition ~10 K. A small conventional exchange bias (CEB) is established with the advent of spontaneous phase separation down to 10 K. Giant ZEB and enhanced CEB effects are found only below 10 K and are attributed to the large unidirectional anisotropy at the interface of isothermally field induced ferromagnetic phase and canted antiferromag…
We report on the observation of exchange bias and memory effect in double perovskite Sr$_2$FeCoO$_6$. Antiphase boundaries between the ferromagnetic and antiferromagnetic regions in the disordered glassy phase is assumed as responsible for the observed effect which reflects in the cooling field dependence and temperature evolution of exchange bias field and in training effect. The spin glass phase itself is characterized through memory, ageing and magnetic relaxation experiments. The spin glass transition temperature, $T_g$, versus $H_{dc}^{2/3}$ follows the Almeida-Thouless line yielding a fr…
We propose experimental verification and theoretical explanation of magnetic anomalies in the complex Fe-contained double perovskite multiferroics like PbFe$_{1/2}$Nb$_{1/2}$O$_3$. The theoretical part is based on our model of coexistence of long-range magnetic order and spin glass in the above substances. In our model, the exchange interaction is anisotropic, coupling antiferromagnetically $z$ spin components of Fe$^{3+}$ ions. At the same time, the $xy$ components are coupled by much weaker exchange interaction of ferromagnetic sign. In the system with spatial disorder (half of corresponding…
We investigated the perpendicular exchange bias (PEB) switching from negative- to positive-exchange bias state for Cr2O3/Pt/Co exchange coupling thin film system exhibiting positive exchange bias phenomena. By changing Pt spacer layer thickness or measurements temperature, we demonstrated the control of two kind of intermediate state of the switching; the double hysteresis loop indicating local, non-averaged PEB, and single hysteresis loop indicating averaged PEB. We proposed the way to control the lateral ferromagnetic domain though the control of PEB magnitude.
In this work, we demonstrate a massive intrinsic exchange bias (3 kOe) in epitaxial CoFe2O4(111) thin films deposited on Al2O3(0001) substrates. This exchange bias is indicative of intrinsic exchange or a ferromagnetic material combined with an antiferromagnet. The analysis of structure, magnetism and electronic states corroborate that there is an interfacial layer CoO between the CoFe2O4(111) thin film and the Al2O3(0001) substrate. The power-law thickness dependence of the intrinsic exchange bias verifies its interfacial origin. This work suggests interfacial engineering can be an effective …
The exchange bias effect in compensated IrMn3/Co(111) system is studied using multiscale modeling from "ab initio" to atomistic calculations. We evaluate numerically the out-of-plane hysteresis loops of the bi-layer for different thickness of the ferromagnetic layer. The results show the existence of a perpendicular exchange bias field and an enhancement of the coercivity of the system. In order to elucidate the possible origin of the exchange bias, we analyze the hysteresis loops of a selected bi-layer by tuning the different contributions to the exchange interactions across the interface. Ou…
We investigated the temperature dependence of the magnetic damping in the exchange biased Pt/ Fe50Mn50 /Fe20Ni80 /SiOx multilayers. In samples having a strong exchange bias, we observed a drastic decrease of the magnetic damping of the FeNi with increasing temperature up to the blocking temperature. The results essentially indicate that the non-local enhancement of the magnetic damping can be choked by the adjacent antiferromagnet and its temperature dependent exchange bias. We also pointed out that such a strong temperature dependent damping may be very beneficial for spintronic applications.
We have investigated the domain wall (DW) dielectric response of potassium dihydrogen phosphate (KH2PO4) crystal under 0-500V dc-bias electric field. Activated DW-contribution onsets freezing at Tf(ω, V), some 27K below the ferroelectric TC; timescale τf(T, V) exhibiting Vogel-Fulcher (VFT) divergence. Sharply distinct low- and high-field behaviors of TC(V), DW-Tg(V), VFT-T0(V), barrier energy Ua(V), and DW glass-fragility m(V) signify a field-induced transition from randomly-pinned/vitreous to clustered/glass-ceramic phases of domain wall matter. Field-hysteresis (ε'poled > ε'unpoled) observe…
We report an exchange bias of more than $2700\,$Oe at room temperature in MnN/CoFe bilayers after high-temperature annealing. We studied the dependence of exchange bias on the annealing temperature for different MnN thicknesses in detail and found that samples with $t_{\text{MnN}}>32\,$nm show an increase of exchange bias for annealing temperatures higher than $T_{\text{A}}=400\,^{\circ}$C. Maximum exchange bias values exceeding $2000\,$Oe with reasonably small coercive fields around $600\,$Oe are achieved for $t_{\text{MnN}}= 42, 48\,$nm. The median blocking temperature of those systems is de…
In this paper I report, exchange bias effect in a bilayer thin film of amorphous zinc ferrite and nanocrystalline gallium ferrite. The amorphous zinc ferrite layer was deposited at room temperature (Ts = RT) on top of a nanocrystalline gallium ferrite thin film using a pulsed laser. This bilayer film showed large exchange bias effect (He ~ 418 Oe at 2 K). The exchange bias shift decreased exponentially as the temperature increased and disappeared for T > 30 K. Along with the exchange bias shift the film also showed enhanced magnetization in Field Cooled (FC) measurements as compared to the Zer…
Understanding the interplay among different magnetic exchange interactions and its physical consequences, especially in the presence of itinerant electrons and disorders, remains one of the central themes in condensed matter physics. In this vein, the coupling between antiferromagnetic and spin glass orders may lead to large exchange bias, a property of potential broad technological applications. In this article, we report the coexistence of antiferromagnetic order and spin glass behaviors in a quasi-one-dimensional iron telluride TaFe$_{1+x}$Te$_3$ ($x$=0.25). Its antiferromagnetism is believ…
We investigated the influence of the Ta buffer layer on the thermal stability of polycrystalline Ta/ MnN/ CoFeB exchange bias systems, showing high exchange bias of about 1800 Oe at room temperature. The thermal stability of those trilayer systems is limited by nitrogen diffusion that occurs during annealing processes. Most of the nitrogen diffuses into the Ta buffer layer, which is necessary for good crystal growth of MnN and thus a crucial component of the exchange bias system. In order to improve the thermal stability, we prepared exchange bias stacks where we varied the Ta thickness to loo…
Exchange biased composites of ferromagnetic single-domain Ni nanoparticles embedded within large grains of MnO have been prepared by reduction of Ni$_x$Mn$_{1-x}$O$_4$ phases in flowing hydrogen. The Ni precipitates are 15-30 nm in extent, and the majority are completely encased within the MnO matrix. The manner in which the Ni nanoparticles are spontaneously formed imparts a high ferromagnetic- antiferromagnetic interface/volume ratio, which results in substantial exchange bias effects. Exchange bias fields of up to 100 Oe are observed, in cases where the starting Ni content $x$ in the precur…
We investigate the motion of magnetic domain walls driven by magnetic fields and current-driven spin-orbit torques in an exchange-biased system with perpendicular magnetization. We consider Cr2O3/Co/Pt trilayers as model system, in which the magnetization of the Co layer can be exchanged-biased out-of-plane or in-plane depending on the field cooling direction. In field-driven experiments, the in-plane exchange bias favors the propagation of the domain walls with internal magnetization parallel to the exchange bias field. In current-driven experiments, the domain walls propagate along the curre…
Exchange bias training effect in ferromagnetic/antiferromagnetic bilayers is investigated. In some systems the evolution of the exchange bias field $H_E$ with the number of cycle $n$ cannot be fitted by the empirical $1/\sqrt{n}$ function. A unified expression is derived from a discretized Landau-Khalatnikov equation in the framework of the thermodynamics model which is proposed by Ch.\ Binek. This generalized model describes well training effect independent of the magnetization reversal mechanism in the ferromagnetic layers.
We studied exchange bias in magnetic multilayers incorporating antiferromagent CoO doped with up to 35 atomic percent of Pt. The exchange bias increased with doping in epitaxial films, but did not significantly change in polycrystalline films at the lowest measured temperature of 5 K, and decreased at higher temperatures. We explain our results by the increased granularity of the doped antiferromagnetic films, resulting in simultaneous enhancement of the uncompensated spin density and reduction of the magnetic stability of antiferromagnetic grains.
K. Mallick and P. S. A. Kumar had reported exchange bias effect in Mg-ferrite thin films, deposited on Si substrate (with a buffer layer of MgO) using Pulsed Laser Deposition (PLD) technique. The authors had presented the temperature dependence exchange bias effect, field dependence exchange bias effect and training effect of a selected Magnesium ferrite thin film of thickness 132 nm. These studies were followed by the film thickness dependence of exchange bias effect. However, the data presented for the 132 nm thick film shows mutually contradicting values in each and every figures. Here, I p…
We present a micromagnetic approach to exchange bias (EB) in ferromagnetic (FM)/antiferromagnetic (AFM) thin film systems with a small number of irreversible interfacial magnetic moments. We express the exchange bias field $H_{EB}$ in terms of fundamental micromagnetic length scale---the exchange length $l_{ex}$. The benefit from this approach is a better separation of a term related to FM layer from a term related to FM/AFM coupling at interfaces. Using this approach we estimate the highest limit of $H_{EB}$ in real FM/AFM systems.
Positive exchange bias has been observed in the Ni$_{81}$Fe$_{19}$/Ir$_{20}$Mn$_{80}$ bilayer system via soft x-ray resonant magnetic scattering. After field cooling of the system through the blocking temperature of the antiferromagnet, an initial conventional negative exchange bias is removed after training i. e. successive magnetization reversals, resulting in a positive exchange bias for a temperature range down to 30 K below the blocking temperature (450 K). This new manifestation of magnetic training is discussed in terms of metastable magnetic disorder at the magnetically frustrated inte…
The exchange bias at ferromagnetic/antiferromagnetic interfaces strongly depends upon the state of antiferromagnetic (AF) layer which, due to strong magnetoelastic coupling, is sensitive to mechanical stresses. In the present paper we consider magnetoelastic effects that arise at FM/AF interface due to lattice misfit and magnetic ordering. We show how magnetostriction affects mutual orientation of AF and FM vectors and easy-axis direction in thin AF layer. The results obtained could be used for tailoring exchange biased systems.
Ensemble-averaged exchange bias in arrays of Fe/FeF2 nanodots has been deconvoluted into local, microscopic, bias separately experienced by nanodots going through different reversal modes. The relative fraction of dots in each mode can be modified by exchange bias. Single domain dots exhibit a simple loop shift, while vortex state dots have asymmetric shifts in the vortex nucleation and annihilation fields, manifesting local incomplete domain walls in these nanodots as magnetic vortices with tilted cores.
By means of layer resolved ion irradiation the mechanisms involved in the irradiation driven modifications of the exchange bias effect in NiFe/FeMn bilayers have been investigated. It is shown that not only the locations of the defects but also the magnetic coupling between both layers during the irradiation process is of crucial importance. This requires an extension of current models accounting for defects in exchange bias systems.
Temperature and PtCo composition dependence of exchange bias in PtxCo1-x/CoO bilayers is investigated. It is observed that exchange bias properties, blocking temperature and magnetic anisotropy of the PtxCo1-x/CoO thin films are strongly affected by the concentration of Pt at the common interface. A detailed structural analysis of antiferromagnetic CoO has been done by x-ray photoelectron spectroscopy (XPS). The XPS data revealed that CoO layer grows with non-stoichiometric behavior which results in other cobalt oxide phases and thus lowers blocking temperature for the exchange biased systems.…
We report magnetization and magetoresistance measurements in hybrid ferromagnetic metal/semiconductor heterostructures comprised of MnAs/(Ga,Mn)As bilayers. Our measurements show that the (metallic) MnAs and (semiconducting) (Ga,Mn)As layers are exchange coupled, re- sulting in an exchange biasing of the magnetically softer (Ga,Mn)As layer that weakens with layer thickness. Magnetoresistance measurements in the current-perpendicular-to-the-plane geometry show a spin valve effect in these self-exchange biased bilayers. Similar measurements in MnAs/p- GaAs/(Ga,Mn)As trilayers show that the excha…
Thin highly epitaxial BiFeO$_3$ films were prepared on SrTiO$_3$ (100) substrates by reactive magnetron co-sputtering. Detailed MOKE measurements on BiFeO$_3$/Co-Fe bilayers were performed to investigate the exchange bias as a function of the films thicknesses and Co-Fe stoichiometries. We found a maximum exchange bias of H$_{\mathrm{eb}}$=92 Oe and a coercive field of H$_{\mathrm{c}}$=89 Oe for a 12.5 nm thick BiFeO$_3$ film with a 2 nm thick Co layer. The unidirectional anisotropy is clearly visible in in-plane rotational MOKE measurements. AMR measurements reveal a strongly increasing coerc…
When a ferromagnet is in proximity with an antiferromagnet, lateral length scales such as the respective magnetic domain sizes drastically affect the exchange bias. Bilayers of FeF2 and either Ni, Co or Fe are studied using SQUID and spatially resolved MOKE. When the antiferromagnetic domains are larger than or comparable to the ferromagnetic domains, a local, non-averaging exchange bias is observed. This gives rise to unusual and tunable magnetic hysteresis curves.
We present results of a study of tunnel junction aging in which the early time dynamics are captured by in situ monitoring of electrical properties of Al-AlOx-Al planar tunnel junctions beginning when the deposition of the counterelectrode is complete. The observed stretched exponential dependences of the conductance and the capacitance manifest hierarchically constrained dynamics imposed by correlated relaxations of interface traps. Bias voltage is used as a control parameter to create bias-dependent aging trajectories that exhibit memory and age-dependent relaxations. Simple tunnel barrier a…
Exchange bias stems from the interaction between different magnetic phases and therefore it generally occurs in magnetic multilayers. Here we present a large exchange bias in a single SrRuO3 layer induced by helium ion irradiation. When the fluence increases, the induced defects not only suppress the magnetization and the Curie temperature, but also drive a metal-insulator transition at a low temperature. In particular, a large exchange bias field up to around 0.36 T can be created by the irradiation. This large exchange bias is related to the coexistence of different magnetic and structural p…
Second harmonic generation magneto-optic Kerr effect (SHMOKE) experiments, sensitive to buried interfaces, were performed on a polycrystalline NiFe/FeMn bilayer in which areas with different exchange bias fields were prepared using 5 KeV He ion irradiation. Both reversible and irreversible uncompensated spins are found in the antiferromagnetic layer close to the interface with the ferromagnetic layer. The SHMOKE hysteresis loop shows the same exchange bias field as obtained from standard magnetometry. We demonstrate that the exchange bias effect is controlled by pinned uncompensated spins in t…
The magnetization reversal in stripe-like exchange bias patterned $\rm Ni_{81}Fe_{19}/IrMn$ thin films was investigated by complementary inductive and high resolution magneto optical magnetometry, magneto optical Kerr microscopy, and polarized neutron reflectometry to clarify the effects of competing interfacial exchange bias and lateral interface contributions. Structures of varying ferromagnetic layer thickness and stripe period were analyzed systematically at the frozen-in domain state of oppositely aligned stripe magnetization. For all samples the mean magnetization of the magnetic hybrid …
We report structural and magnetic properties of multilayers composed of thin layers of the half metallic ferromagnetic Heusler compound Co2MnGe and layers of Au, Cr and the Heusler compound Cu2MnAl. The hysteresis loops measured at low temperatures reveal the existence of an exchange bias field HEB in all of these multilayers. For the [Co2MnGe/Au] multilayer system HEB is largest reaching up to 1 kOe at a temperature of 2 K. We characterize the exchange bias phenomenon in detail and show that it originates from a spin glass type of magnetic order for a thin interlayer at the interfaces. We dis…
Magnetization and magnetic microstructure of top soft magnetic layer (Fe), which is exchange spring coupled to bottom hard magnetic layer ($L1_0$ FePt) is studied using high resolution Kerr microscopy. When the sample (FePt/Fe) is at remanent condition of hard magnetic layer, considerable shifting of Fe layer hysteresis loop from centre i.e., exchange bias phenomena is observed. It is observed that one can tune the magnitude of exchange bias shift by reaching the remanent state from different saturating fields ($H_{SAT}$) and also by varying the angle between measuring field and $H_{SAT}$. The…
A new characteristic is observed in the training effect of perpendicular exchange bias. For Pt/Co/Pt/IrMn multilayers with perpendicular magnetic anisotropy, the magnetization reversal process is accompanied by pinned domain wall motion and the asymmetry of hysteresis loop is always equal to zero during subsequent measurements. It is interesting to find that the exchange field decreases greatly as a function of the cycling number while the coercivity almost does not change. It is clearly demonstrated that the training effect of perpendicular exchange bias strongly depends on the magnetization …
Here, we report both ac and dc magnetization, thermodynamic and electric properties of hexagonal Ba$_3$NiIr$_2$O$_9$. The Ni$^{2+}$ (spin-1) forms layered triangular-lattice and interacts antiferromagnetically while Ir$^{5+}$ is believed to act as magnetic link between the layers. This complex magnetic interaction results in magnetic frustration leading to a spin-glass transition at $T_f$ $\sim$ 8.5 K. The observed magnetic relaxation and aging effect also confirms the nonequilibrium ground state. The system further shows large exchange bias which is tunable with cooling field. Below the Curie…
We discuss the annealing-dependence of exchange bias in Ga1-xMnxAs epilayers that are overgrown with Mn. Although pure Mn is a known antiferromagnet, we find that the as-grown Mn overlayer does not produce any exchange coupling with Ga1-xMnxAs. Rather, our studies indicate that annealing in air is essential for creating the standard signatures of an exchange bias (a clear shift in the magnetization hysteresis loop and an increased coercive field). We use x-ray photoelectron spectroscopy to characterize the compositional depth profile of both as-grown and rapid thermal annealed samples. These s…
We investigated an out-of-plane exchange bias system that is based on the antiferromagnet MnN. Polycrystalline, highly textured film stacks of Ta / MnN / CoFeB / MgO / Ta were grown on SiO$_x$ by (reactive) magnetron sputtering and studied by x-ray diffraction and Kerr magnetometry. Nontrivial modifications of the exchange bias and the perpendicular magnetic anisotropy were observed both as functions of film thicknesses as well as field cooling temperatures. In optimized film stacks, a giant perpendicular exchange bias of 3600 Oe and a coercive field of 350 Oe were observed at room temperature…
While the principal features of the exchange bias between a ferromagnet and an antiferromagnet are believed to be understood, a quantitative description is still lacking. We show that interface spin disorder is the main reason for the discrepancy of model calculations versus experimental results. Taking into account spin disorder at the interface between the ferromagnet and the antiferromagnet by modifying the well known Meiklejohn and Bean model, an almost perfect agreement can be reached. As an example this is demonstrated for the CoFe/IrMn exchange biased bilayer by analyzing the azimuthal …
We investigated the influence of doping antiferromagnetic MnN in polycrystalline MnN/CoFe exchange bias systems, showing high exchange bias of up to 1800 Oe at room temperature. The thermal stability of those systems is limited by nitrogen diffusion that occurs during annealing processes. In order to improve the thermal stability, defect energies of elements throughout the periodic table substituting Mn were calculated via density functional theory. Elements calculated to have negative defect energies bind nitrogen stronger to the lattice and could be able to prevent diffusion. We prepared exc…
In this work, IrMn$_{3}$/insulating-Y$_{3}$Fe$_{5}$O$_{12}$ exchange-biased bilayers are studied. The behavior of the net magnetic moment $Δm_{AFM}$ in the antiferromagnet is directly probed by anomalous and planar Hall effects, and anisotropic magnetoresistance. The $Δm_{AFM}$ is proved to come from the interfacial uncompensated magnetic moment. We demonstrate that the exchange bias and rotational hysteresis are induced by the irreversible switching of the $Δm_{AFM}$. In the training effect, the $Δm_{AFM}$ changes continuously. This work highlights the fundamental role of the $Δm_{AFM}$ in th…
A detailed study of exchange-biased Fe/MnF2 bilayers using magneto-optical Kerr Effect shows that the magnetization reversal occurs almost fully through domain wall nucleation and propagation for external fields parallel to the exchange bias direction. For finite angles phi between bias and external field the magnetization is aligned perpendicular to the field cooling direction for a limited field range for decreasing fields. For external fields perpendicular to the bias direction the magnetization aligns with the field cooling direction for descending and ascending fields before fully reversi…
A detailed study of the exchange bias effect and the interfacial electronic structure in Ni/Co3O4(011) is reported. Large exchange anisotropies are observed at low temperatures, and the exchange bias effect persists to temperatures well above the Neel temperature of bulk Co3O4, of about 40 K: to ~80 K for Ni films deposited on well ordered oxide surfaces, and ~150 K for Ni films deposited on rougher Co3O4 surfaces. Photoelectron spectroscopy measurements as a function of Ni thickness show that Co reduction and Ni oxidation occur over an extended interfacial region. We conclude that the exchang…
The exchange interaction between nanostructured components is an effective way to enhance the magnetic properties of materials. This effect is used in exchange-coupled magnetic composites, which properties are governed by synergetic impact of constituent phases. Texturing is one of the problems that needs to be solved in order for such composites to be used in industry. In this work, we performed experimental and micromagnetic investigation of the exchange-bias properties in Co/Co3O4 nanocomposites based on nanorods array. Specifically, we investigated how the resulting properties will change …
The temperature dependence of exchange bias properties are studied in polycrystalline $ \mathrm{BiFeO_3} / \mathrm{Ni_{81}Fe_{19}} $ bilayers, for different $ \mathrm{BiFeO_3} $ thicknesses. Using a field cooling protocol, a non-monotonic behavior of the exchange bias field is shown in the exchange-biased bilayers. Another thermal protocol, the Soeya protocol, related to the $ \mathrm{BiFeO_3} $ thermal activation energies was carried out and reveals a two-step evolution of the exchange bias field. The results of these two different protocols are similar to the ones obtained for measurements p…
We report a large exchange-bias (EB) effect after zero-field cooling the new tetragonal Heusler compound Mn2PtGa from the paramagnetic state. The first-principle calculation and the magnetic measurements reveal that Mn2PtGa orders ferrimagnetically with some ferromagnetic (FM) inclusions. We show that ferrimagnetic (FI) ordering is essential to isothermally induce the exchange anisotropy needed for the zero-field cooled (ZFC) EB during the virgin magnetization process. The complex magnetic behavior at low temperatures is characterized by the coexistence of a field induced irreversible magnetic…
