J. K. Furdyna

We studied the temperature dependence of the specific contact resistance (AR_C) of the copper/GaMnAs interface in the range from 15 K to 290 K. This range includes the Curie temperature of the GaMnAs film of about 145 K. AR_C is typically as low as 1×10^{- 7}Ωcm², and decreases slowly with decreasing temperature T. However, as T approaches Curie temperature (T_C), AR_C jumps to about double its value. We suggest that this behavior arises from the suppression of one of the two spin conduction channels, resulting in substantial spin polarization. This might offer a convenient scheme to estimate the spin polarization at a single ferromagnetic/nonferromagnetic (F/N) interface using all-electrical measurements.

DOI:https://doi.org/10.1103/PhysRevB.78.159904

We report comprehensive temperature and photoexcitation intensity dependent studies of the photoinduced magnetization precession in Ga_1-xMn_xAs (x = 0.035) by time-resolved Kerr rotation measurements. We observe coherent oscillations of local Mn spins triggered by an ultrafast photo-induced reorientation of the easy axis due to changes in the magnetic anisotropy. The amplitude saturation of these oscillations above certain pump intensity is indicative of stabilization of the magnetic easy axis orientation on temperatures above ~Tc/2. We find that the observed magnetization precession damping (Gilbert damping) is strongly dependent on pump laser intensity, but largely independent of ambient temperature.

We have used polarized neutron reflectometry to study the structural and magnetic properties of the individual layers in a series of (Al,Be,Ga)As/(Ga,Mn)As/GaAs/(Ga,Mn)As multilayer samples. Structurally, we observe that the samples are virtually identical except for the GaAs spacer thickness (which varies from 3-12 nm), and confirm that the spacers contain little or no Mn. Magnetically, we observe that for the sample with the thickest spacer layer, modulation doping by the(Al,Be,Ga)As results in (Ga,Mn)As layers with very different temperature dependent magnetizations. However, as the spacer layer thickness is reduced, the temperature dependent magnetizations of the top an bottom (Ga,Mn)As layers become progressively more similar - a trend we find to be independent of the crystallographic direction along which spins are magnetized. These results definitively show that (Ga,Mn)As layers can couple across a non-magnetic spacer, and that such coupling depends on spacer thickness.Comment: Submitted to Physical Review

Kerr rotation and magnetic circular dichroism (MCD) were measured in thin epitaxial layers of the narrow gap ferromagnetic semiconductors InMnSb and InMnAs grown by low‐temperature molecular beam epitaxy. The measurements were carried out in the wavelength range from 400 to 7000 nm at saturated magnetization conditions. The wavelength dependence of Kerr rotation and MCD have been successfully modeled using the same set of parameters. To calculate the Landau level energies for the above systems we have employed the Pidgeon‐Brown model combined with an exchange matrix, as described by Rigaux. Taking into account transition energies corresponding to the selection rules for right‐ and left hand circularly polarized light enabled us to calculate both the Kerr rotation and MCD using procedures described by Lang et al. The fits give reliable values for the sign and magnitude of the exchange parameters N₀α and N₀β.