Size-dependent magnetocaloric effect in GdVO4 nanoparticles.

• Nanocrystal GdVO 4 presents enhanced paramagnetic-like behavior with the reduction of grain size. • The enhanced paramagnetic-like behavior leads to a giant entropy change of -Δ S M = 45 J/kg K at 3 K for Δ = H = 7 T. • The decrease of the saturated magnetization and -Δ S M with the grain size reduce to 30 nm is due to the aggregation effec. • Introducing paramagnetism in AFM materials provides a promising way to adjust the magnetic entropy of these materials. We investigated the magnetization and electron spin resonance (ESR) in nanocrystals of antiferromagnet GdVO 4 with the grain size ranging from 30 nm to 5 µm. Our nanoparticles with an average size reduction from 5 µm to 300 nm exhibited enhanced paramagnetic-like behavior, in which the weakly coupled spins can be well aligned along the direction of an external magnetic field, resulting in a giant entropy change of -Δ S M = 45 J/kg K at 3 K for Δ H = 7 T. Moreover, with a further reduction of grain size to ~ 30 nm, the saturation magnetization together with the negative entropy change -Δ S M , max decreased dramatically. The aggregation effect is believed to be responsible for the decline in -Δ S M , max , in which small nanoparticles agglomerating to 'large' grains made them behave like bulk material. Finding the critical point of positive size effect on magnetocaloric effect offered a new way to achieve large magnetic entropy change. [ABSTRACT FROM AUTHOR]