Rare-earth energy levels and magnetic properties of HoPO₄and ErPO₄

Abstract

The static and dynamic magnetic responses of HoPO4 and ErPO4 have been studied by means of neutron spectroscopy and magnetic susceptibility measurements. The inelastic neutron scattering spectra exhibit well-defined transitions characteristic of crystal-field excitations of the rare-earth ions. A comparison of the neutron data with optical absorption and both non-resonance and resonance Raman scattering measurements has been made. The derived crystal-field-level structure provides a basis for explaining the low-temperature magnetic properties of both compounds. The calculated and measured paramagnetic susceptibilities agree well for HoPO4 and ErPO4 in the temperature range of 5-300 K. The highly anisotropic, saturated magnetization of the ground doublet in HoPO4 may act as a 'bootstrap' for a long-range magnetic ordering of the moments parallel to the c-axis at low temperatures. The nearly spherically symmetric moments of the low-lying Kramers doublets of ErPO4, however, tend to couple less effectively via exchange interactions.