Electron Spin Resonance in Nickel-Doped Germanium

Abstract

Electron spin resonance absorption proportional in intensity to the ${\mathrm{Ni}}^{\ensuremath{-}}$ concentration has been detected at 14 kMc/sec in germanium crystals. The spectrum, which consists of six main lines having anisotropic $g$ values, is interpreted in terms of a Jahn-Teller distortion of the nickel ion in any cubic direction. The principal axes of the $g$ tensor are the cubic direction and two mutually perpendicular [110] directions having $g$ values of 2.0294, 2.0176, and 2.1128, respectively. Hyperfine structure due to ${\mathrm{Ni}}^{61}$ in enriched samples shows the same principal axes and principal values of \ensuremath{\le}1.6, 12.2, and 10.3, respectively, in units of ${10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$, and establishes the spin of that isotope as $\frac{3}{2}$. Hyperfine interaction with ${\mathrm{Ge}}^{73}$ in the two nearest neighbor positions toward which the nickel atom moves in the Jahn-Teller distortion has been resolved and ranges from 19.8\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ for the magnetic field in the Ni-${\mathrm{Ge}}^{73}$ direction to 16.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ at right angles to this axis. Above 20.4\ifmmode^\circ\else\textdegree\fi{}K the Jahn-Teller distortion reorients with increasing rapidity. The line broadening and eventual merging has been studied and estimates have been made of the activation energies for reorientation by inversion and by rotation.