Enhanced survival of short-range magnetic correlations and frustrated interactions in R ₃T intermetallics

Elastic and inelastic neutron scattering and magnetization measurements have been used to study peculiarities of the magnetic state in R ₃T compounds (R=Gd, Er, Tb; T=Ni, Co) below and above magnetic ordering temperatures. A pronounced non-Brillouin shape of the magnetization curves observed in the antiferromagnetic compounds Gd ₃Ni and Tb ₃Ni above their magnetic ordering temperatures together with earlier reported data about the retention of the magnetic contribution to the total specific heat of Gd ₃T and anomalous behavior of the electrical resistivity above magnetic ordering temperatures are ascribed to the existence of short-range magnetic correlations in the wide temperature range in the paramagnetic state. The persistence of short-range magnetic order up to temperatures greater than 56 times the Néel temperature has been revealed by powder neutron diffraction measurements performed for Tb ₃Ni and Tb ₃Co. On the other hand, results from inelastic neutron scattering show that the low temperature magnetic excitations are strongly suppressed in both Tb ₃Co and Er ₃Co. It is suggested that the extended short-range magnetic correlations, which turn out to be an inherent feature of R ₃T type compounds, are due to the layered crystal structure and to the difference between geometrically frustrated intra-layer exchange interactions and inter-layer exchange.