Abstract:
Molecular beam epitaxy has been employed to obtain Ga
1−xMn
xN films with
x up to 10% and Curie temperatures
TC up to 13 K. The magnitudes of
TC and their dependence on
x,
TC(x)∝xm, where
m=2.2±0.2, are quantitatively described by a tight-binding model of superexchange interactions and Monte Carlo simulations of
TC. The critical behavior of this dilute magnetic insulator shows strong deviations from the magnetically clean case (
x=1), in particular, (i) an apparent breakdown of the Harris criterion, (ii) a nonmonotonic crossover in the values of the susceptibility critical exponent
γeff between the high temperature and critical regimes, and (iii) a smearing of the critical region, which can be explained either by the Griffiths effects or by macroscopic inhomogeneities in the spin distribution with a variance
Δx=(0.2±0.1)%.
Notes:
cited By 42
Publisher's Version
