Magnetic diffuse scattering in Tb3Ga5O12 and Tb3Al5O12 garnets

In geometrically frustrated systems, long-range magnetic ordering is usually suppressed down to very low temperatures. While in the so-called spin liquid phase, magnetic diffuse scattering is observed. The physical origin of such scattering is not well understood. Using neutron scattering and DC, AC magnetic susceptibility measurements on Tb3Ga5O12 and Tb3Al5O12, we observed magnetic diffuse scattering and unusual paramagnetic behavior. The M-T curve at high magnetic field does not coincide with the one at low fields below $\sim $10 K. This indicates that magnetic correlations are gradually developing around that temperature. The nonlinear response of the AC susceptibility suggests that the diffuse scattering may originate from critical scattering, which has also been observed in frustrated spinel systems. This might indicate the realization of soft (magnon) modes in the spin liquid phase.