Abstract: Quadrupole energy shifts of low temperature iron Mössbauer lines in amorphous magnets

Abstract

The 57Fe Mössbauer effect has been used to study the hyperfine Zeeman pattern below the spin ordering or spin freezing temperature in amorphous magnets. At very low temperatures, for which the electronic magnet moments approach their saturation values, it is a common dictum of the amorphous Mössbauer literature that the effects of quadrupole energy are now contained only in the linewidths and line shapes of the six Mössbauer lines and not in their positions.1,2 A previously unsuspected quadrupole shift of the nuclear Zeeman lines in amorphous magnets has been observed by 57Fe Mössbauer spectroscopy in speromagnetic amorphous yttrium iron garnet of 4.2 K. The distinctive shift pattern, with the symmetry −3, +1, −1, +1, −1, +3, is shown to arise theoretically as a second-order perturbation of the Zeeman levels by the distribution of electric field gradients in the amorphous state. It is observed to have a magnitude which conforms quantitatively with the theoretical expectation. 1T. E. Sharon and C. C. Tsuei, Phys. Rev. B 5, 1047, (1972). 2C. L. Chien and R. Hasegawa, Phys. Rev. B 16, 3024 (1977).