Power-law behavior of the temperature dependence of magnetic anisotropy of uncapped ultrathin Fe Films on GaAs(001)

The temperature dependence of the magnetic anisotropy and magnetization M of d=5-20 mono-layer (ML) thick Fe films on {4x6}GaAs(001) has been measured using in situ ferromagnetic resonance and a superconducting quantum interference device from 40 to 400 K. We find a reduced magnetization for d < 7 ML and for all films a Curie temperature T-c > 400 K. From a full angular, thickness and temperature-dependent analysis we determine second K-2(T) and fourth K-4(T) order magnetic anisotropy constants as well as the temperature dependence of the surface-interface K-2 perpendicular to(s,eff)(T) and volume K-2 perpendicular to(v)(T) contributions to the out-of-plane uniaxial anisotropy. The low-temperature values are K-2 perpendicular to(s,eff)(T -> 0)=1.26 +/- 0.1x10(-3)J/m(2) (649 +/- 51.5 mu eV/atom) and K-2 perpendicular to(v)(T -> 0)=4 +/- 9x10(4) J/m(3) (3 +/- 6.7 mu eV/atom). The temperature dependence of K-2 perpendicular to(T)/K-2 perpendicular to(0) for 5 ML Fe on {4x6}GaAs(001) is proportional to [M(T)/M(0)](Gamma) with an exponent Gamma=2.9 +/- 0.2 being very close to the theoretically expected one.