Spatially Resolved Inhomogeneous Ferromagnetism in $(\mathrm{Ga},\mathrm{Mn})\mathrm{As}$ Diluted Magnetic Semiconductors: A Microscopic Study by Muon Spin Relaxation

Thin epitaxial films of the diluted magnetic semiconductor (DMS) GaMnAs have been studied by low energy muon spin rotation and relaxation ($\mathrm{LE}\mathrm{\text{−}}\mu \mathrm{SR}$) as well as by transport and magnetization measurement techniques. $\mathrm{LE}\mathrm{\text{−}}\mu \mathrm{SR}$ allows measurements of the distribution of magnetic field on the nanometer scale inaccessible to traditional macroscopic techniques. The spatial inhomogeneity of the magnetic field is resolved: although homogeneous above $T_c$, below $T_c$ the DMS consists of ferromagnetic and paramagnetic regions of comparable volumes. In the ferromagnetic regions the local field inhomogeneity amounts to 0.03 T.

Figure 1

Muon spin relaxation spectra in GaAs:2.2%Mn in zero external magnetic field below the FM transition at $T_c=60\mathrm{K}$ (red dots) and above it (blue dots).

Figure 2

(a) Resistivity and (b) magnetization before (green dots) and after (red stars) annealing of GaAs:6%Mn. (c) Temperature dependences of the fast (black squares) and slow (red dots) muon relaxation rates in the annealed sample. (d) Corresponding magnetic fractions.

Figure 3

Muon spin relaxation spectra in GaAs:6%Mn below the FM transition at $T=10\mathrm{K}$ (red dots) and above it at $T=170\mathrm{K}$ (blue dots) in transverse magnetic field $B_{\mathrm{ext}}=26\mathrm{mT}$. For both spectra the precession frequencies correspond to external magnetic field.