The crystal fields in α-alums-a high pressure magnetic resonance study

Abstract

The origin of the crystal field and its variation with temperature in several α-alums have been studied bynmr of ²⁷Al and epr of Cr³⁺ at high hydrostatic pressures and low temperatures. The results lead to an explanation of the anomalous temperature variation of the axial crystal field at the trivalent ion site. The mechanism of the phase transition in ammonium alum is also explained. A correlation between the axial crystal field as determined bynmr (e²qQ/h) and that determined by epr (D) has been obtained.