Noncubic symmetry in Ca1-xEuxB6 (0.15 less than or similar to x <= 1.00): An electron-spin-resonance study

The Eu2+ (4f(7), S=7/2) g value in Ca1-xEuxB6 (0.15 less than or similar to x <= 1.00) was measured by means of electron spin resonance at two frequencies (fields), 9.4 (approximate to 3.4 kOe) and 34.4 GHz (approximate to 12.1 kOe). The g value was found to be anisotropic and magnetic-field dependent. The amplitude of the anisotropy increases at low temperatures. The observed angular and temperature dependences of the g value suggest tetragonal symmetry caused, presumably, by a distortion along a direction perpendicular to the largest crystal face, the [001] direction. Due to the platelet shape of the samples, part of the anisotropy of the g value can also be attributed to demagnetization effects. The g values decrease at higher fields, which is interpreted in terms of a two-band model involving an exchange interaction between the localized Eu2+ 4f(7) electrons with conduction Eu2+ 5d-like electrons and B 2p-like holes. (C) 2006 American Institute of Physics.99