Giant exchange bias behavior and training effect in spin-glass-like NiCr2O4/NiO ceramics

Abstract

NiCr 2 O 4 /NiO ceramic has been synthesized successfully through co-precipitation method to study the magnetic properties. Field cooling (FC) magnetic hysteresis loops measured at low temperature show significant shift in both coercive field and remnant magnetization. It has been plotted that the exchange bias (EB) field can be as large as 11.86 kOe at 10 K followed with an enhanced coercive field. The variation of EB field and shift of remnant magnetization after FC processes shows a regular tendency with increasing temperature and cooling field. Known as training effect, the EB behavior also presents a strong dependence on loop cycle. The cycle dependence of large EB field, vertical shift of magnetization, and coercive field at low temperature can be ascribed to the pinned spins in spin-glass-like (SGL) phase of the system interface. The SGL phase has been proved by Almeida-Thouless line and high field relaxation effect. The disorder structure is responsible for the frustration interface and the formation of SGL phase in the interface.

NiO Nanoparticle Synthesis Using a Triblock Copolymer: Enhanced Magnetization and High Specific Capacitance of Electrodes Prepared from the Powder

“…Such an effect has been explained to arise because of the magnetic interaction at the interface between a FM and an AFM phase. , At lower temperatures, exchange interaction is maximum, but at higher temperatures, the magnetic moments both in core and in shell are free to reverse with applied magnetic field, and thus, there is no shift in the hysteresis loop. In the present system of NiO nanoparticles synthesized using the P123 triblock copolymer, the exchange bias effect was much larger than those reported earlier. , We ascribe such high values of magnetization observed to the presence of Ni 3+ ions, which contribute to uncompensated magnetic spins in the otherwise AFM NiO system. This in addition to the oxygen vacancies at the nanoparticle surfaces gives rise to a high value of magnetization in the system.…”

“…In the present system of NiO nanoparticles synthesized using the P123 triblock copolymer, the exchange bias effect was much larger than those reported earlier. 37,48 We ascribe such high values of magnetization observed to the presence of Ni 3+ ions, which contribute to uncompensated magnetic spins in the otherwise AFM NiO system. This in addition to the oxygen vacancies at the nanoparticle surfaces gives rise to a high value of magnetization in the system.…”

“…The magnetization obtained is much higher than that reported earlier in the case of NiO nanoparticles. 47,48 Magnified views of M – H curves for low values of H are shown in Figure 8b. For FC M–H measurements, the sample that was cooled down to respective temperatures under 3 T magnetic fields exhibited an exchange bias effect, indicating the presence of unidirectional anisotropy.…”

Effect of spin glass frustration on exchange bias in NiMn/CoFeB bilayers

“…γ H is the characteristic decay rate of the training effect and defined as γ H =b/(K 2 ζ) where K is a constant proportional to the exchange coupling strength in FM/AFM system, ζ is the inverse of relaxation time and b is another constant 25 . The small value of γ H indicates large deviation from equilibrium steady state and hence large training effect which is according to relaxation theory 29 . Such spin configurational relaxation in training effect data is also reported for a FM-SG interface.…”

Exchange bias and spin glass behavior in biphasic NiFe2O4/NiO thin films

“…Moreover, the situation becomes more complicated if a spin glass-like (SG) phase is present, which is often the case in nanoparticle or nanogranular EB systems synthesized by mechanical [19][20] (ball milling) or wet-chemical methods [21,22]. In these cases, the disordered spins in the spin glass phase can couple to the reversible phase at low temperatures, yielding EB and anomalous vertical shifts of hysteresis loops.…”