Exchange Bias Field Research Articles

Significant Surface Spin Effects and Exchange Bias in Iron Oxide-Based Hollow Magnetic Nanoparticles.

Exchange bias (EB) properties have become especially important in hollow magnetic nanoparticles (MNPs) due to the versatility and reduced size of these materials. In this work, we present the synthesis and study of the EB properties of iron-oxide-based hollow MNPs and their precursors Fe/iron oxide MNPs with core/void/shell structure. The two mechanisms involved in EB generation were investigated: the frozen spins present in the nanograins that form the nanoparticles and the surface spins. The effect of external parameters on the coercivity (HC), remanence (MR), exchange bias field (HEB) and frozen spins, such as cooling field (HFC) and temperature, was investigated. Both HC and HEB present a maximum threshold above which their values begin to decrease with HFC, showing a new trend of HEB with HFC and allowing modulation on demand. The existence of surface spins, present on the outer and inner surfaces, was demonstrated, and an intrinsic EB phenomenon (HEB = 444 Oe for hollow iron oxide-based MNPs of 13.1 nm) with significant magnetization (MS~50 emu/g) was obtained. Finally, core/void/shell MNPs of 11.9 nm prior to the formation of the hollow MNPs showed a similar behavior, with non-negligible HEB, highlighting the importance of surface spins in EB generation.

Extrinsic negative magnetization and exchange bias: Impact of the SmCrO3 particle size

Polycrystalline SmCrO3 with particle sizes between 106 and 527 nm were prepared by controlling the annealing temperature, and the particle size effects on their structural and magnetic properties were systematically investigated. Analysis of magnetic data indicates that the maximum magnetization was enhanced upon increasing the particle size and the negative magnetization observed under nominal zero-field-cooling conditions was caused by a negative trapped field. Interestingly, the exchange bias effect can also be tuned by modulating the particle size. The zero-field-cooling exchange bias field (HEB) and the remnant magnetization shift (MEB) had nonmonotonic relationships with the particle size, whereas the field-cooling HEB and MEB decreased monotonically with increasing particle size. The ratio of Cr3+/Cr6+ and the potential surface spin disorder are discussed based on X-ray photoelectron and Raman spectral results to determine the ferromagnetic/antiferromagnetic contributions, whose interfacial anisotropic energy was considered responsible for the tunable exchange bias. Overall, these results presented herein suggest new ways to optimize the properties of SmCrO3 materials for applications in the magnetic storage.

Emergence of exchange bias and giant coercive field enhancement by internal magnetic frustration in La0.67Sr0.33MnO3 thin films

We have studied the influence of controlled defects on the magnetic properties of La0.67Sr0.33MnO3 (LSMO) thin films. We used 100 nm thick epitaxial LSMO films, which were grown on SrTiO3 substrates and introduced stoichiometry changes and defects using oxygen ion irradiation through nanoporous alumina masks. Oxygen irradiation through the mask creates cascades of defects in spatially-modulated regions in the plane of the LSMO film. The magnetic properties of the samples were compared before and after the irradiation. We have found that irradiation reduces the ferromagnetic ordering temperature, decreases the total magnetization, enhances the coercivity, and induces exchange bias below 50 K. The coercivity enhancement is dramatically higher below 50 K and can be associated with exchange bias. These results can be explained by the formation of Mn-rich antiferromagnetic or ferrimagnetic phases within the bombarded regions that are exchange coupled to the non-irradiated - ferromagnetic host.

Spin glass and exchange bias phenomena in NdSrNiMnO6 nanoparticles: Role of antiferromagnetic antisite disorders

We report the discovery of spin glass (SG) and exchange bias (EB) phenomena in NdSrNiMnO6 nanoparticles. Doping at Nd site in the double perovskite compound Nd2NiMnO6, induces antisite disorders leading to antiferromagnetic antiphase boundaries within the system, which are further responsible for the observed phenomena. The role of particle size on these effects has been discussed as the amount of antisite disorder may vary with particle size. We observed a high Curie temperature (TC ∼ 264 K) for small size samples. As the particle size increases, the ferromagnetic (FM) transition becomes indistinct and system transforms to a magnetically frustrated state containing co-existence of FM, antiferromagnetic (AFM) and SG phases. Meanwhile, TC decreases with increasing particle size and the FM ordering becomes unclear for largest particle size sample. The detail investigation of ac susceptibility, memory effect, DC magnetization and magnetic relaxation measurements exposes the SG behavior in the largest particle size sample. By varying the amount of antisite disorders in the NdSrNiMnO6 with increasing particle size, we obtained intrinsic EB effect with a large EB field (∼640 Oe). Further, the EB effect has also been explored by carrying out the cooling field dependent EB measurements in addition to training effect experiments. The exchange interaction between the AFM core and SG like shell of the system is explained through a phenomenological core shell model.

Ionization and Displacement Damage on Nanostructure of Spin–Orbit Torque Magnetic Tunnel Junction

Spin–orbit torque magnetic tunnel junction (SOT-MTJ) is the memory cell of magnetic random access memory (MRAM), which is a promising candidate for upper level cache in the harsh environment due to nonvolatility, high speed, and high endurance. Therefore, it is significant to research the mechanism of irradiation effects on the SOT-MTJ before its integration onboard. This article investigates the ionization and displacement damage of in-plane magnetic anisotropy SOT-MTJ, including 1-MeV electron and 17.2-keV He <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> Co gamma irradiations with various fluences and doses, respectively. The devices are resilient to tunnel magnetoresistance (TMR), whereas the magnetic properties are changed after irradiation. The 100-Mrad (Si) gamma and 17.2-keV He <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> irradiations generate similar damages on the device performances, in the aspects of the magnetic anisotropy and critical current density ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$J_{\mathrm {c}}$ </tex-math></inline-formula> ). However, the displacement damage originating from the electron irradiation does not have a significant influence on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$J_{\mathrm {c}}$ </tex-math></inline-formula> . In addition, the saturation magnetization and exchange bias field are changed by irradiations without regularity. Some possible mechanisms are discussed to explain the experimental results through the simulation of stopping and range of ions in matter (SRIM) and microstructural tests.

Influence of polarity compensation on exchange bias field in LaMnO&lt;sub&gt;3&lt;/sub&gt;/LaNiO&lt;sub&gt;3&lt;/sub&gt; superlattices

Perovskite superlattices have received enormous attention in recent years, for they possess several new phases of quantum matter. In particular, an unexpected exchange bias effect in (111)-oriented superlattices composed of ferromagnetic LaMnO&lt;sub&gt;3&lt;/sub&gt; and paramagnetic LaNiO&lt;sub&gt;3&lt;/sub&gt; is observed, which has aroused broad interest. In this work, three kinds of LaMnO&lt;sub&gt;3&lt;/sub&gt;/LaNiO&lt;sub&gt;3&lt;/sub&gt; superlattices with (001), (110), and (111) out-of-plane orientation are fabricated by pulsed laser deposition, and also studied systemically. It is found that the superlattices are epitaxially grown on the SrTiO&lt;sub&gt;3&lt;/sub&gt; substrates without strain relaxation. The superlattices have a monolayer terraced structure with a surface roughness below 0.1 nm. Electrical transport measurements reveal a Mott conducting behavior with strong localization of electrons in the superlattices. All the superlattices with different orientations exhibit exchange bias phenomenon. The field cooling and zero field cooling curves indicate that there are two different magnetic components in the superlattice in a low temperature range. Further analysis of the values of exchange field reveals that the exchange bias field is related to the orientation and polarity of the superlattices. Different superlattices form different charged planes stacked along out-of-plane orientation, leading to a polarity match/mismatch at the interface between the superlattices and substrates. The surface reconstructions that act as compensating for the polar mismatch influence the exchange bias field of the superlattices. It is observed that the intensities of the exchange field of the polar-matched superlattices are higher than those of the polar-mismatched superlattices at different temperatures. These results are helpful in further understanding the magnetoelectric transport properties in the perovskite superlattices.

Effect of albumin coating on the magnetic behavior of Mn ferrite nanoclusters.

The effect of clustering induced by albumin coating on the magnetic behaviour of ultra-small MnFe2O4 nanoparticles has been systematically investigated and compared with that in pure Mn ferrite nanoparticle dense assembly, using a mesoscopic scale approach and numerical simulations reproducing the experimental findings well. Our results provide evidence that in the coated system, the interplay between intra-particle and intra-cluster exchange interactions strongly affects the exchange bias and coercive field values, with the dipolar interactions playing a minor role. Instead, the albumin coating does not affect the thermal stability of the observed superspin glass phase, the freezing temperature being similar in the coated and uncoated systems.

Exchange bias effect of current Joule thermally modulated inverted vertical (Co/Pt) n/Co/IrMn nanomultilayers

The exchange bias has a crucial influence on the key performance parameters of magneroresistive sensor, which has wide applications in many fields. This paper presents a method that uses the Joule heating effect combined with a magnetic field to modulate the exchange bias in magnetic multilayers. By this method, we systematically modulate the in-plane exchange bias field (&lt;i&gt;H&lt;/i&gt;&lt;sub&gt;eb&lt;/sub&gt;) in the inverted (Co/Pt)&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt;/Co/IrMn structure (&lt;i&gt;n&lt;/i&gt; + 1 is the repetition of the Co layers), here the thickness of the Pt layer is smaller than that of the Co layer. In these inverted structures, the &lt;i&gt;H&lt;/i&gt;&lt;sub&gt;eb&lt;/sub&gt; can be continuously modulated by changing the amplitude of a pulse current &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;DC&lt;/sub&gt; (an in-plane magnetic field &lt;i&gt;H&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt;) after fixing an &lt;i&gt;H&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt; (&lt;i&gt;I&lt;/i&gt;&lt;sub&gt;DC&lt;/sub&gt;). In more detail, the &lt;i&gt;H&lt;/i&gt;&lt;sub&gt;eb&lt;/sub&gt; deceases gradually by increasing the &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;DC&lt;/sub&gt; and its polarity of the &lt;i&gt;H&lt;/i&gt;&lt;sub&gt;eb&lt;/sub&gt; can be reversed finally, which will not disappear even under a large &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;DC&lt;/sub&gt;. Furthermore, if both the amplitude and direction of &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;DC&lt;/sub&gt; (&lt;i&gt;H&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt;) are changed, with a &lt;i&gt;H&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt; (&lt;i&gt;I&lt;/i&gt;&lt;sub&gt;DC&lt;/sub&gt;) fixed, a reversal of &lt;i&gt;H&lt;/i&gt;&lt;sub&gt;eb&lt;/sub&gt; can be realized from positive (negative) to negative (positive) direction under a large &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;DC&lt;/sub&gt;. From here, one may find that the modulation of the exchange bias in our text is totally different from the normal case one thinks, where the &lt;i&gt;H&lt;/i&gt;&lt;sub&gt;eb&lt;/sub&gt; becomes zero under a large enough &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;DC&lt;/sub&gt; due to the pure heating effect. Therefore, we believe that the above results show that our method can modulate in situ the linear field range and sensitivity, which has important significance in guiding the optimization of the performance parameters of magneroresistive sensors.

Inverse dependence of exchange bias and coercivity on cooling field caused by interfacial randomization in nanosystems with Co sparsely distributed in CoFe2O4 matrix

We conceive a model of nanosystems where Co is uniformly, randomly distributed into a CoFe2O4 (CFO) matrix, and study the influences of composition and CFO antiferromagnetic exchange coupling (JCFO) on zero-field-cooled/field-cooled magnetization behavior and the dependencies of exchange bias field (HE) and coercivity (HC) on Co/CFO interfacial coupling (JCo/CFO), composition and cooling field (HFC), based on a modified Monte Carlo method. With decreasing temperature, the zero-field-cooled and field-cooled magnetization curves are overlapped and increasing initially, and then splitting at a critical temperature (TP), below which the field-cooled magnetization continues increasing while the zero-field-cooled magnetization exhibits a peak and drops, indicating a magnetically frozen state. A larger JCFO induces an elevated TP and a reduced magnetization, while the opposite results are obtained by a higher Co occupation fraction (PCo). On the other hand, HE is nonmonotonic with JCo/CFO and the peak decreases and shifts to a lower JCo/CFO value for a larger PCo. HC increases monotonically with increasing JCo/CFO. Moreover, HE is inversely proportional to PCo when PCo varies from 0.11 to 0.30, indicating the exchange bias is still an interfacial effect. Finally, for a nonzero JCFO, HE may be suppressed and accompanied by the recovery of HC with increasing HFC. Otherwise, HC for zero JCFO becomes high and insensitive to HFC. It is ascribed to the uniform contact between Co and CFO, leading to the Co magnetization reversal and the CFO magnetization precisely controlled by HFC. This work opens a new avenue to control the exchange bias in nanosystems through interfacial randomization.

Photo-controlled exchange bias in CoO@Co–Fe PBA core–shell heterostructures

After red irradiation, the exchange bias field of the CoO@Co–Fe PBA hybrid reduces by ∼50%. In addition, the value of HEB can be further regulated accurately by setting the irradiation time or adjusting the incident light frequency.

A numerical study on the interplay between the intra-particle and interparticle characteristics in bimagnetic soft/soft and hard/soft ultrasmall nanoparticle assemblies.

A mesoscopic scale approach and the Monte Carlo (MC) method have been employed to study the exchange bias behaviour of MnFe2O4 (soft)/maghemite (soft) and CoFe2O4 (hard)/maghemite (soft) nanoparticles (NPs) of size ∼ 3 nm in dense and diluted assemblies at low temperatures. The analysis of our MC results clearly shows that in the powder samples the contribution to the exchange bias field (Hex) and the coercivity (Hc) comes mainly from the intraparticle core/shell structure in the hard/soft sample and that the interplay between the internal characteristics and the interparticle interactions is more important in the soft/soft samples where the dipolar strength is enhanced. In the diluted frozen ferrofluid samples where interparticle exchange interactions are absent and the role of the dipolar interactions is not significant the exchange bias effects are reduced, and they come from the intra particle structure. The variation of Hex and Hc with the applied cooling field well reproduces the experimental findings and sheds light on the key mechanisms of the observed magnetic behaviour. Our results demonstrate the possibility to control the magnetic behaviour of nanostructures by using properly chosen core/shell bimagnetic nanoparticles.

Field-free spintronic terahertz emitters based on IrMn/Fe/Pt exchage bias heterostructures

Spintronic terahertz (THz) emitter has more advantages such as lower cost, broader spectrum and easier operation than the commercial THz emitters, and thus has become a focus of research towards the next-generation THz source. However, in such a spintronic THz emitter, an external magnetic field is technologically required to align the orientation of the magnetization, which is detrimental for practical applications. Here, a spintronic terahertz emitter based on IrMn/Fe/Pt exchange bias structure is presented. By means of ultrafast spin injection on Fe/Pt interface followed by the spin-to-charge conversion in Pt, plus the effective magnetic field originating from the IrMn/Fe interface, the THz pulse with considerable intensity can be generated in such a structure without the assistance of external field. Besides, the remanent magnetization for thin Fe layer is enhanced by inserting an ultrathin Cu layer between the IrMn surface and the Fe surface, which is beneficial to the field-free THz emission. The range of obtained dynamic THz spectrum exceeds 60 dB and the positive saturation field can reach up to ~ –10 mT by optimizing the multilayer thickness, meeting the standard for commercial application. By rotating the sample, it is found that the polarization direction of the generated THz wave circulates simultaneously and keeps perpendicular to the direction of exchange bias field in the film plane. Moreover, we design a spin valve THz emitter based on the structure of IrMn/Fe/Pt/Fe by adding a free ferromagnetic Fe layer into the exchange bias multilayers. The emitted THz pulse amplitude is larger for the antiparallel alignment of the Fe layers at zero field than for the parallel alignment or exchange bias structure. The present work shows that the spin terahertz emitter based on IrMn/Fe/Pt exchange bias structure can produce the considerable terahertz signals without external field. Furthermore, the polarization direction of the emitted THz signal can be easily manipulated by rotating the sample. Because of this series of advantages, such exchange bias heterostructures are expected to play an important role in designing the next-generation THz source.

Tunable exchange bias in La1.5Sr0.5CoMnO6 double perovskite doped with nonmagnetic Ga ions

The crystal structure, electronic structure, and magnetic behaviors of nonmagnetic Ga ions doped double perovskite La1.5Sr0.5CoMnO6 single phase crystals have been investigated. Different from the traditional magnetic dilution effect of nonmagnetic doping, Ga doping in La1.5Sr0.5CoMnO6 enhances the ferromagnetic (FM) exchange interaction of Co3+-O-Mn3+. Moreover, both conventional and spontaneous exchange bias (EB) effects can be tuned by modulating the Ga doping content, which is accompanied by the variation of the Co3+/4+ and Mn3+/4+ and the effective magnetic moment. The EB field and magnetization can be improved by nonmagnetic Ga3+ doping with content lower than 0.2. The evolution of conventional and spontaneous EB effects in La1.5Sr0.5Co1-xGaxMnO6 can be understood in terms of the unidirectional interface anisotropic coupling between FM/anti-FM, and/or FM/spin glass, which is affected by antisite disorder, spin glass, and the uncompensated coupling between Co and Mn.

Observation of giant exchange bias effect in Ni–Mn–Ti all-d-metal Heusler alloy

We report a giant exchange bias (EB) field of about 3.68 kOe during field cooled process in all-d-metal Ni40(FeCo)4Mn36Ti20 Heusler alloy. The study of magnetic memory effect and isothermal magnetic relaxation processes suggest that the giant EB field arises due to the possible coexistence of antiferromagnetic (AFM) and ferromagnetic (FM) phase exchange interaction in the studied system at temperatures below 35 K. Furthermore, the temperature and cooling field dependence of EB effect are analyzed which are related to the change in unidirectional anisotropy at FM/AFM interface. The study of a well-established training effect confirms the intrinsic nature of the observed EB behavior. This result will open up a new way toward the development of EB materials considering all-d-metal Heusler alloy systems.

Hard/soft magnetic trilayer: Monte Carlo simulation

We present computer models of three-layer (trilayer) hard/soft magnetic heterostructures for the study of magnetic reversal processes under the external magnetic field using the Monte Carlo method. The comparisons of data for the magnetic SmCo/Fe trilayer models with the results for the magnetic SmCo/Fe bilayer model are presented. For the SmCo/Fe trilayer heterostructures, the exchange-bias field Hex and the irreversibility field Hirr increase by 150% and 30%, respectively, than for the SmCo/Fe bilayer model. Phase diagrams of dependencies of the Hex and Hirr values on the thickness of the hard magnetic layer of the trilayer magnetic heterostructures are plotted.

Realization of exchange bias control with manipulation of interfacial frustration in magnetic complex oxide heterostructures

Rich exchange bias (EB) behaviors were previously observed when ferromagnetic (FM) materials contacted a spin glass, demonstrating magnetic degrees of freedom of the coupling between the glass and FM spins. However, the correlation between the degree of magnetic spin frustration and the strength of the resulting EB is far from being understood. Here, we systematically investigate the dependency of EB on interfacial spin frustration in magnetic complex oxide heterostructures including ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}\text{/}\mathrm{CaMn}{\mathrm{O}}_{3}$ (LCMO/CMO) systems. The experimental analysis revealed that the extent of interfacial spin frustration is determined by the subtle competition between different types of magnetic orders related to the glassy spin behaviors at the interface. Such spin frustration can be manipulated through strain engineering through changes in the Mn ${e}_{g}$ orbital by alternating the stacking sequence of the heterostructures. A highly tunable EB field with 95% change of strength between the highly and weakly frustrated heterostructures has been achieved. Magnetic depth profiles of the heterostructures provide convincing evidence that a magnetically depressed region always occurs in the LCMO layer at the LCMO/CMO interfaces irrespective of the stacking sequence. Finally, EB is established at the magnetic interface in the LCMO layer.

Magnetization reversal, field-induced transitions and H–T phase diagram of Y1−x Ce x CrO3

We report a systematic study of the magnetic phase diagram in the H–T plane, negative magnetization (NM), exchange interactions and field-induced spin–flop transitions in the distorted perovskite Y1−x Ce x CrO3. Locked AFM and weak-FM configurations in Γ4(G z , F y , A x ) phase of YCrO3 (S = 3/2 ground state) unlocks into the Γ2 (F z , G y , C x ; ) phase of the canted AFM and FM structures with the dilute substitution of Ce (x ⩾ 0.05). The asymmetric and symmetric exchange interaction (J AS ∼ 0.11 meV and J S ∼ 0.85 meV) between the trivalent Ce and Cr enable the positive quartic-anisotropy field ( ∼ 2.85 × 102 Oe) along with the second order anisotropy field ( ∼ 5.93 × 102 Oe). Unlike the pristine YCrO3 compound, the Ce incorporated system exhibits a giant fourth-order anisotropy constant (K 4 = 1.35 × 105 erg/c.c.) due to the asymmetric exchange interaction between the trivalent Ce–Cr which further lifts the free energy of the system and causes lag in the onset of AFM ordering showing the significant thermal hysteresis (ΔT ∼ 10 K) in the field-cooled (FC)-warming measurement protocol as compared to the FC-cooling mode. The H–T phase diagram, mapped from the isothermal magnetization data and differential magnetic susceptibility data with different measurement protocols clearly distinguishes three prominent regions below the T N (∼150 K), viz (i) long-range canted AFM + weak FM phase (Γ4 (G z , F y , A x )), (ii) Γ24 mixed phase and (iii) robust Γ2 (F z , G y , C x ; , ) AFM + FM phases. Tunable spin–flopped transition (∼ 30 kOe), significant negative exchange-bias field (H EB ∼ 2.5 kOe), huge coercive field (H C ∼ 22 kOe) and large NM (ΔM ∼ 280 emu/mole) are the unique characteristic features of the current investigated system.

Exchange Coupling in Synthetic Anion‐Engineered Chromia Heterostructures

AbstractControl of magnetic states by external factors has garnered a mainstream status in spintronic research for designing low power consumption and fast‐response information storage and processing devices. Previously, magnetic‐cation substitution was the conventional approach to induce ferromagnetism in an intrinsic antiferromagnet. Theoretically, anion doping is proposed to be another means to change magnetic ground states. Here, the authors demonstrate the synthesis of high‐quality single‐phase chromium oxynitride thin films using in‐situ nitrogen doping. Unlike antiferromagnetic monoanionic chromium oxide and nitride phases, chromium oxynitride exhibits a robust ferromagnetic and insulating state, as demonstrated by the combination of multiple magnetization probes and theoretical calculations. With increasing the nitrogen content, the crystal structure of chromium oxynitride transits from trigonal (Rc) to tetragonal (4 mm) phase and its saturation magnetization reduces significantly. Furthermore, they achieve a large and controllable exchange bias field in the chromia heterostructures by synthetic anion engineering. This work reflects the anion engineering in functional oxides towards potential applications in giant magnetoresistance and tunnelling junctions of modern magnetic sensors and read heads.

Temperature lag with the onset of exchange bias, superparamagnetic blocking, and antiferromagnetic ordering in ultrathin ferromagnet/antiferromagnet thin film

The magnetization of a nanosized magnet, such as an ultrathin film, thermally fluctuates and can become superparamagnetic. In ferromagnetic/antiferromagnetic thin films, superparamagnetism can be suppressed in accordance with antiferromagnetic ordering. The exchange bias can also be induced at the ferromagnetic/antiferromagnetic interface, and it is nontrivial whether the superparamagnetic blocking temperature (TB_SPM) can match either the onset temperature of the exchange bias (TB_EB) or the Néel temperature (TN). In this study, we investigated the temperature dependence of parameters such as coercivity, exchange bias field, magneto-optic Kerr rotation (θK), and AC magnetization (MAC) to elucidate the matching of TB_EB, TB_SPM, and TN in a Pt/Co/Au/Cr2O3/Pt thin film. Based on the temperature dependences of MAC, TB_SPM was yielded as about 283 K. TB_EB and TN, which were determined based on the temperature dependence of θK, were 278 and 282 K, respectively. TB_SPM was almost equal to TN but TB_EB was smaller. This temperature lag was caused by the difference in the magnetic anisotropy energy required to induce the exchange bias and suppress superparamagnetism.

Computer Simulation of Exchange Bias Field at the Ferromagnetic-Antiferromagnetic Boundary

This paper presents computer simulation results for a bilayer system with ferromagnetic and antiferromagnetic films. The dependence of the exchange bias field on the external magnetic field for this system is calculated. The Heisenberg model and the Wolf cluster algorithm are used for calculations. The reason for the appearance the bias field is the interaction between spins at the films interface. An increase the external magnetic field leads to a nonlinear increase the bias field. There are two reasons for nonlinearity. First, the external magnetic field suppresses antiferromagnetic ordering. Second, an external magnetic field-ordered ferromagnetic has an inverse effect on the antiferromagnetic film.