MAGNETOOPTICAL MICROWAVE SPECTROSCOPY OF THE COHERENT MAGNETIC STATE IN THE MIXED-VALENCE COMPOUND SMB6 IN THE FREQUENCY-RANGE 40-120 GHZ

In undoped pure single crystals of the mixed valence compound SmB6 ano malous ESR absorption is observed in the frequency range v=40-120 GHz at temperatures of 1.8-4.2 K. The ESR for the case of the coherent gro und state consists of two components corresponding to g-factors g(1)=1 .907+/-0.003 and g(2)=1.890+/-0.003. The amplitude of both ESR lines s trongly depends on temperature in the temperature range studied: the a mplitude of the first line with g=g(1) increases and the amplitude of the second line decreases with temperature. A model based on considera tion of intrinsic defects in the SmB6 crystalline lattice, with a dens ity similar to 10(15)-10(16) cm(-3), is suggested as an explanation fo r the anomalous ESR-behavior. In the frequency range v>70 GHz at T=4.2 K, in addition to the main ESR lines, a new magnetic resonance with a hysteretic field dependence is discovered. (C) 1996 American Institut e of Physics.