Exchange bias effect in spin glass CoCr2O4 nanoparticles

Abstract

CoCr2O4 nanoparticles are about 5.4nm in diameter synthesized by a hydrothermal technique. Magnetization measurements reveal that the nanoparticles exhibit a spin glass behavior below glass transition temperature. Signature of memory effect is clear in reheating curve where the step-like shape increasing with the increase of temperature is recovered after cooling process. Magnetic relaxation is performed to prove memory effect. Ageing effect is also detected in CoCr2O4 nanoparticles to verify the spin glass behavior. As temperature decreases to 5K, which is far below the glass transition temperature, exchange bias effect can be observed clearly accompanied with a shift in field-cooled hysteresis loop. As particle size decreases to 5.4nm, spin glass behavior appears due to the increased spin disorder effect. The spin glass phase providing a pinning force from some frozen spins to the rotatable spins gives the key to explain the exchange bias effects.