Orbitally Anisotropic Exchange and Crystal Field Effects on the Magnetic Susceptibility of (Eu[sub x]Y[sub 1−x])[sub 2]O[sub 3

Abstract

The importance of orbital anisotropy in the exchange interaction has been discussed by several authors recently. Huang and Van Vleck introduced this anisotropic exchange to interpret the enhancement of the magentic susceptibility of cubic Eu2O3 over that of the free Eu3+ ions. Considering only the effect of the crystal field V within the first excited state of Eu3+, they proposed that the anisotropic exchange might be opposite in sign and five times greater than the conventional isotropic one. Recent experiments by Kern and Kostelecky have shown that at 4.2°K the susceptibility per Eu3+ ion in (EuxY1−x)2O3 is relatively independent of x, suggesting that the exchange interactions have no net effect. In order to understand this, a detailed calculation for the effect of V on the susceptibility is carried out using the spectroscopic data in Y2O3:Eu3+. It is found that the measured susceptibility can be attributed to the mixing of different J levels by V without invoking the exchange. This enables one to conclude that the effective anisotropic exchange could be at most comparable to the isotropic one but opposite in sign, and hence the susceptibility would not vary significantly with Eu concentration at low temperatures.