Training effect of exchange bias inγ−Fe2O3coatedFe

Abstract

Training effect of exchange bias in the ␥-Fe 2 O 3 coated Fe nanoparticles were studied. The experimental results indicate that the frozen spins in ␥-Fe 2 O 3 shells are responsible for both the horizontal and vertical shifts of the field-cooling hysteresis loops. To understand exchange bias and training effect in the nanoparticles, we modified the Stoner-Wohlfarth model by adding the unidirectional anisotropy energy term to the total energy. It is found that the exchange bias and training effect in the nanoparticles can be well interpreted within the modified model. Since the configuration of the frozen spins was gradually varying as the applied field cycled for the hysteresis loop measurements, the number of the spins frozen along the cooling-field direction decreased, consequently, the exchange bias field H E became smaller.

Exchange bias in structure-phase separated K0.8Fe2−xNixSe2 (x=0.015) single crystal: Interface evidence

“…It is well known that the temperature evolution of H E is typical for EB systems with FM-SG phases [7,8,28,29]. In order to confirm the configuration established above, the temperature dependence of EB field and coercivity were measured from 3 K to 300 K after FC condition with H c ¼ 20 kOe, as shown in Fig.…”

“…2 and 4, the Ni doped samples show spin glass behavior as temperature decreases, indicating the first one might be applicable in our sample. In fact, the existence of spin glass interfaces have been demonstrated in shell-structure g-Fe 2 O 3 /Fe 3 O 4 nanoparticles [7], Fe/g-Fe 2 O 3 nanoparticles [28,29]. Therefore, for the x ¼0.015 sample, the mechanism of unidirectional anisotropy is probably due to the exchange coupling at the interfaces of between the FM regions (phase 2) and the surrounding SG regions.…”

Exchange bias and its training effect in Ni/NiO nanocomposites

“…5, we have plotted H E as a function of M (30 kOe) of powders milled for 3 h. Ohldag et al [15] have proposed that a small fraction of the interfacial spins is pinned, leading to a shift of the hysteresis loop. To some extent, the moment of these pinned [7]. It is clear that H E depends quite linearly on M for loops cycled n > 1.…”

“…Zheng et al have reported that the EB training effect in ␥-Fe 2 O 3 coated Fe nanoparticles can be well explained in terms of the modified Stoner-Wohlfarth model [7]. The decrease of the number of frozen spins along the cooling field direction reduces the EB field upon subsequent field cycling.…”

Tailoring the exchange bias of Ni/NiO nanogranular samples by the structure control

“…[1], Section 3.2). Therefore, estimating the real influence of structure and microstructure on the EB properties is a very difficult task and, actually, only a few systematic studies exist [5,[18][19][20][21][22][23].…”