Evidence of large nonlinear magnetic effects in the paramagnetic phase of GaFeO3

Magnetic susceptibility and magnetization measurements have been performed on a polycrystalline sample of GaFeO3 and compared with X-band electronic spin resonance (ESR) experiments. The persistence of nonlinear effects in the presence of relatively low external fields is observed far above the ferrimagnetic transition. The temperature evolution of the ESR spectra indicates the increase of spin-spin interactions accompanied by significant changes in the internal field as the nonlinear regime becomes more important. This suggests the existence of ferrimagnetic short-range spin correlations induced by the external field over a wide temperature range above the magnetic ordering transition.