Prediction of reentering and switching ferromagnet/antiferromagnet exchange bias by antiferromagnetic proximity effect

Abstract

Exchange bias (EB) in ferromagnet/antiferromagnet (FM/AF) core/shell nanoparticles can be used to beat the superparamagnetic limit, and these core/shell nanoparticles are commonly fabricated by the ferromagnetic cores that are naturally oxidized to form an antiferromagnetic shell. The drawbacks of this method are that the EB effect is weak and hard to be controlled due to the shell passivation effect. Thus a theoretical work is conceived where the FM/AF core/shell nanoparticles are embedded into an antiferromagnetic matrix, and an antiferromagnetic proximity effect is induced to modulate the FM/AF EB effect in a controlled way. The results show that the shell/matrix proximity may enhance the magnetic stabilization of nanoparticles to generate the core/shell EB if the matrix is a hard AF. On the other hand, a rigid core/shell EB can switch its sign through thermal training by using a softly antiferromagnetic matrix. The local magnetization behaviors and energy barrier variations during magnetizing well interpreted the simulation results. It is evidenced that the proximity effect can optimize the magnetic properties of the pinning antiferromagnetic layer at will, ranging from statically magnetic stability to dynamically magnetic relaxation. This work opens fascinating possibilities for engineering of magnetic materials with desired magnetic properties, which has led to a surge in both experimental and theoretical investigations.

Magnetocrystalline anisotropy imprinting of an antiferromagnet on an amorphous ferromagnet in FeRh/CoFeB heterostructures

“…Then, the magnetization hysteresis loop is recorded by isothermal cycling of H between 1.0J SM /gμ B and −1.0J SM / gμ B at constant steps of |0.02J SM /gμ B |, where g is the Landé g-factor and μ B is the Bohr magneton. At each temperature/field value, 10 5 Monte Carlo steps were used to equilibrate the system and then discarded, followed by 10 5 Monte Carlo steps for averaging magnetization quantities 25,26 . Finally, 50 sets of independent initial spin states were chosen to minimize the errors.…”

Spin‐Glass Irreversibility Temperature and Magnetic Stabilization in Ferromagnet/Spin‐Glass Bilayers

“…In summary, irreversibility properties in SG is demonstrated, and using SG to couple to ferromagnet, T B EB can enhanced largely through properly reducing J SG , and in ferromagnet/ antiferromagnet systems, one has to resort to auxiliary pinning layer [29] or antiferromagnetic proximity effect [30] to observe similar phenomena. On the contrary, small J IF and large J SG may play destructive roles on H C in a wide temperature range involving room temperature; otherwise, the temperature dependence of H C exhibits zigzag behavior due to strong link between H C and H E .…”

Spin glass properties mapped by coercivity in ferromagnet/spin glass bilayers

“…, where these values all come from fit results in figure 3 using equation (32). Furthermore, the roughly flat H C curve with J IF at K SG =1.74×10 4 erg cm −3 can be understood due to the fact that the isotropy-to-anisotropy phase transition occurs (seen in figure 4).…”

“…Then the magnetic hysteresis (m-h) loop is recorded by cycling H between −1 and 1 kOe in steps of |ΔH|=10 Oe. To update the spin state undergoing the processes of field cooling and isothermal magnetizing, a modified Monte Carlo Metropolis method is used [5,18,32,33,44]. In the standard Monte Carlo method, the flipping probability of a single moment was only determined by the energy difference between the trial and original states.…”

“…Subsequently, Jalil [30] promoted Xu et al's method at low temperature and conceived five subsidiary states around the minimum energy points as fluctuation states and Du et al [31] extended the fluctuation states to a continuous area as they should be. Finally, Hu et al [32,33] applied this method to interacting systems and have proven that the simulation results obtained are informative for interpreting the hysteresis loop behaviors of systems with finite anisotropies. However, to the best of our knowledge, the K SG in an SG and its role as well as potential application have scarcely been studied experimentally and theoretically.…”