Spin-Orbit Electric Field Gradient in Cubic Ferromagnets: Strong Magnetization-Direction Dependence of the Field Gradient Distribution

Abstract

The electric quadrupole interaction of ${}^{191}\mathrm{Pt}$ ( ${I}^{\ensuremath{\pi}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3/{2}^{\ensuremath{-}}$; ${T}_{1/2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.9\mathrm{d}$) in an Fe single crystal was measured for magnetization $M$ parallel to the crystallographic [100], [110], and [111] axes. For $M\ensuremath{\parallel}[111]$ and [110] the distribution of the electric field gradient (EFG) is relatively sharp. For $M\ensuremath{\parallel}[100]$ the EFG distribution is by a factor of 2.8(6) broader than for $M\ensuremath{\parallel}[111]$. Additional data on Os, Re, Ir, and Au in Fe indicate that this behavior seems to be of general nature: In all cases the EFG distribution for $M\ensuremath{\parallel}[100]$ is considerably broader than for $M\ensuremath{\parallel}[110]$ and [111].