EPR STUDY OF FINE AND HYPERFINE INTERACTIONS OF GD3-X)GD2XSE3 AND PB1-XGDXSE( IN BI2(1)

Electron paramagnetic resonance experiments were performed on Bi2(1-x) Gd2xSe3 and Pb1-xGdxSe samples at room and liquid-helium temperatures. The Gd3+ sites are characterized by hexagonal and octahedral symmetri es in Bi2(1-x)Gd2xSe3 and Pb1-xGdxSe samples, respectively. The absolu te signs of the spin-Hamiltonian parameters in Bi2(1-x)Gd2xSe3 were de termined by comparing the intensities of the lines at room and liquid- helium temperatures: b(2)(0)<0, b(4)(0)>0, and b(6)(0)<0. The \b(2)(0) \ value in Bi2(1-x)Gd2xSe3 increased nonlinearly with decreasing tempe rature, becoming constant below 40 K. At the low temperature of 2.2 K, four hyperfine transitions due to the Gd-155 isotope (I=3/2) were obs erved in Pb1-xGdxSe, leading to the average value of the hyperfine-cou pling constant of 2.55+/-0.10 mT for the two Gd-155 and Gd-157 process ing nonzero nuclear magnetic moments.