Magnetoelastic interactions in the series of rare-earth phosphates RPO4 (R = Tb-Tm)

Abstract

The magnetic and magnetoelastic properties of RPO4 (R = Dy, Ho, Er), which have the zircon-type tetragonal structure, are investigated in the paramagnetic phase within the extended susceptibility formalism. The characteristic behaviour of the first-order magnetic susceptibility allows us to refine the values of the crystalline electric field parameters and to determine the strength of the magnetic interactions. The magnetoelastic coefficients and quadrupolar constants for all the symmetry-lowering modes are then determined from third-order magnetic susceptibility and parastriction measurements. Their coherency within the series of RPO4 is emphasized: all the magnetoelastic couplings keep the same sign and order of magnitude; the tetragonal magnetoelastic coefficients are sizeable in comparison with those determined in the rare-earth intermetallics. The variation of the crystalline electric field interactions and of the magnetoelastic couplings throughout the series of RPO4 (Tb-Tm) is discussed, which is an essential step towards a coherent understanding of the magnetic behaviour of the whole series.