System for ESR measurements at hydrostatic pressures to 60 kilobars

A single‐crystal sapphire serves both as a solid microwave cavity (X band) and an anvil in a Bridgman‐anvil pressure geometry. A metal gasket is used in a manner similar to its use in the diamond‐anvil pressure cell, and single‐crystal samples are subject to purely hydrostatic pressures. The ruby‐fluorescence pressure–measurement technique is utilized. Sample size is limited to a disk approximately 0.6 mm in diameter and 0.1 mm thick. ESR data on Cr3+ in ruby to 60 kilobars are given as an illustration of the precision and data quality. Line widths and profiles, as well as line positions, are meaningful. Very little degradation of the data is experienced at the higher pressures. The first and second derivatives of the zero‐field splitting (δ) of the states in ruby with pressure are measured as dδ/d P= (6.70±0.08) ×10−4 cm−1 kilobar−1 and d 2δ/d P 2= (−2.44±0.30) ×10−6 cm−1 kilobar−2 at P=0. The gyromagnetic ratio g 11 is shown to experience a fractional change less than 2×10−4 to 60 kilobars.