Ferromagnetic resonance ofGa0.93Mn0.07Asthin films with constant Mn and variable free-hole concentrations

Abstract

The magnetic properties of ferromagnetic ${\mathrm{Ga}}_{0.93}{\mathrm{Mn}}_{0.07}\mathrm{As}$ thin films have been investigated by $X$-band ferromagnetic resonance (FMR) spectroscopy as a function of hole concentration. The hole concentration $[p]$ was varied from ${10}^{21}\phantom{\rule{0.3em}{0ex}}\text{to}l{10}^{18}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ by hydrogen passivation. We determined the limit for the onset of ferromagnetism as $[p]\ensuremath{\approx}1\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, the critical temperatures as a function of hole concentration, and the easy and hard axes for magnetization as a function of temperature and hole concentration. The temperature and hole concentration dependences of the magnetocrystalline anisotropy constants were determined. The dominant constant ${K}_{2\ensuremath{\perp}}$ changes for $T=4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ from $\ensuremath{-}8\ifmmode\times\else\texttimes\fi{}{10}^{4}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}+1\ifmmode\times\else\texttimes\fi{}{10}^{4}\phantom{\rule{0.3em}{0ex}}\mathrm{erg}∕{\mathrm{cm}}^{3}$ with decreasing the hole concentration. The anisotropy coefficient ${\ensuremath{\kappa}}_{2}$ varies with the reduced magnetization with an expected quadratic power law. The effective $g$ factor is different from the paramagnetic value of ${\mathrm{Mn}}^{2+}$ of $g=2.00$, due to the hole contribution; it changes from 1.90 to 1.97 with decreasing the hole concentration. In addition to the resonance positions, the FMR linewidth and intensity were analyzed. The FMR linewidth varies with the inverse of the hole concentration. Free energy surfaces are calculated for the simulation of magnetization switching.