Magnetic and electric properties of EuB6

Abstract

Short Notes K133 phys. stat. sol. (b) E, a 3 3 (1979) Subject classification: 14 and 18.2; 19; 21. 7 Instituto Venezolano de Investigaciones Cientdicas, Centro de Fisica, Caracasl) (a) and Institute for Pure and Applied Physical Sciences, University of California, San Diego21 (b) Magnetic and Electric Properties of EuB, BY S. OSEROFF (a), R. CALVO (a), J. STANKIEWICZ (a), Z. FISK (b), and D C JOHNS TON (b) The purpose of this note is to report on what, we believe, a r e the first results of electron spin resonance in a pure single crystal of EuB6 and to compare them with magnetic and electric data previously published for the same sample /l/. Previous ESR measurements were performed on polycrystalline samples by several authors /2, 3/. Trivalent r a r e earth ions form hexaborides with me- tallic behaviour. The Same compounds of divalent ions were supposed to be semiconductors. EuB 6 is a cubic material crystallizing in a structure which may be regarded as CsC1-type a r r a y of Eu atoms and B6 octahedra. It has been believed that EuB6 o r d e r s ferromagnetically and contains only Eu /4/; but recently Isikawa et al. /5/ have reported magnetic and electric data on this material. Their results indicate that EuB6 is semi-metallic, contains some Eu3+, and becomes antiferromagnetic at TN 6 K. However, a more recent investigation of carbon substituted EuBs /6/ indicates that the para- magnetic Curie temperature decreases smoothly with increasing carbon con- tent, that the order changes from ferromagnetic to antiferromagnetic, and that the Eu is divalent. Kasaya et al. /6/ suggest that the data reported in /5/ may be due to carbon contamination. We felt it would be important to measure the electrical and magnetic properties on the same single crystal of pure EuB6. The sample preparation technique has been described previously /I/. ESR measurements were performed at 9 and 35 GHz in the temperature range of 1.4 to 300 K. In the ESR spectrum, we can clearly separate between two temperature regions below and above -30 K. In the high temperature range we observed 1) Apartado 1827, Caracas, Venezuela. 2) San Diego, La Jolla (California), USA.