Cooling field and temperature dependent exchange bias in spin glass/ferromagnet bilayers

Abstract

We report on the experimental and theoretical studies of cooling field (HFC) and temperature (T) dependent exchange bias (EB) in FexAu1 − x/Fe19Ni81 spin glass (SG)/ferromagnet (FM) bilayers. When x varies from 8% to 14% in the FexAu1 − x SG alloys, with increasing T, a sign-changeable exchange bias field (HE) together with a unimodal distribution of coercivity (HC) are observed. Significantly, increasing in the magnitude of HFC reduces (increases) the value of HE in the negative (positive) region, resulting in the entire HE ∼ T curve to move leftwards and upwards. In the meanwhile, HFC variation has weak effects on HC. By Monte Carlo simulation using a SG/FM vector model, we are able to reproduce such HE dependences on T and HFC for the SG/FM system. Thus this work reveals that the SG/FM bilayer system containing intimately coupled interface, instead of a single SG layer, is responsible for the novel EB properties.

Investigating Exchange Bias and Coercivity in Fe3O4–γ-Fe2O3 Core–Shell Nanoparticles of Fixed Core Diameter and Variable Shell Thicknesses

“…Above T M , H EB decreases until it becomes zero again at the blocking temperature, T B (which is 100 or 200 K, depending on the H FC ). Above T B , H EB becomes positive and increases up to 300 K. A similar trend of the temperature dependence of H EB up to 200 K in our samples was reported in spin-glass-ferromagnet bilayers [43] under several H FC . This trend was also reported in polycrystalline Fe–Cr bilayers [44] under only one field-cooling value of H FC = 1 kOe.…”

“…The temperature-driven sign reversal of H EB was attributed to Fe–Cr spin glass. In [43], T 0 and T M were found to decrease with increasing H FC , whereas H EB at T M was found to increase. These observations are almost similar to what we have observed in our core–shell nanoparticle system.…”

Cobalt nanoparticles for biomedical applications: Facile synthesis, physiochemical characterization, cytotoxicity behavior and biocompatibility

“…Moreover, with increase in temperature from 50 K to 200 K, the magnitude of H E increases and exhibits a maximum value of H E =53.33 Oe at 200 K. Typically, the atomic coordination number of the surface spins is different from that of the core and this variation of atomic coordination number causes perturbations in the crystal field which can destabilizes the ferrimagnetic order at the surface[70]. Furthermore, the alignment of spin can have a multiplicity of forms with several different ground states and as a result, the surface layer acts like ''spin glass '' behavior[52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70].Thus, in present study, we expect that the core-shell interaction at the interface gives rise the phenomenon of exchange bias effect and this observed exchange bias effect can support the fact that the surface spins have spinglass-like behavior and surrounds the ferromagnetic core material[71].The coercivity (H C ) value 128.41Oe observed at 300 K, is much larger than that for bulk Co(10 Oe) [9, 64]. It is known that the coercivity of any material referred to measure of the magnetic field strength required to change the direction of magnetization which depends on several factors like magnetic anisotropy, defects, strain, size, doping, nature of the surface, and also the interparticle interaction [72].…”

Magnetic and structural properties of MnRh thin films

“…Therefore, the variation of H C vs T is non-monotonic. 11 The coercivity is an extrinsic property that depends on many factors, e.g. morphology, grain sizes and lattice constants.…”