We report on the new type of photoinduced magnetization in ferromagnetic (Ga,Mn)As thin films. Optically generated spin-polarized holes change the orientation of ferromagnetically coupled Mn spins and cause a large change in magnetization, being 15% of the saturation magnetization, without the application of a magnetic field. The memorization effect has also been found as a trace after the photoinduced magnetization. The observed results suggest that a small amount of nonequilibrium carrier spins can cause collective rotation of Mn spins presumably through the p-d exchange interaction.

The reduction in coercive force by light illumination has been found in ferromagnetic semiconductor heterostructure p-(In, Mn)As/GaSb prepared by molecular-beam epitaxy. Enhanced ferromagnetic coupling between Mn ions, arising from excess photogenerated holes, reduces the domain wall energy and changes the magnetization hysteresis characteristics. The value of coercive force returns to the original value when excess holes recombine with trapped electrons.

Dynamics of photoinduced magnetization rotation was studied in ferromagnetic p-͑Ga,Mn͒As by carefully comparing the temporal profile of the photoinduced polar Kerr rotation with that of the photoinduced reflectivity change. Rotation of ferromagnetically coupled Mn spins is induced by photogenerated hole spins within the excitation pulse width of a 100 fs, whereas relaxation takes place in tens of picosecond as a result of strong damping. Observed results suggest that hole and Mn spins rotate and relax together upon optical excitation. This would be a different type of excitation ͑coupled hole-Mn spin complex͒ appearing in the hole-mediated ferromagnetic system.Recently, magnetization rotation from in-plane to out-ofplane direction by the illumination with circularly polarized cw light has been demonstrated in epilayers of hole-mediated ferromagnetic semiconductor ͑Ga,Mn͒As. 1 The results suggest the occurrence of collective rotation of ferromagnetically-coupled Mn spins induced by the small amount of optically generated hole spins, which can be regarded as novel spin-induced cooperative phenomenon based on the p-d spin-exchange interaction. In this Brief Report, we are concerned with dynamics of the magnetization rotation triggered by the optically injected carrier spins in the ferromagnetic ͑Ga,Mn͒As. Results obtained from photoinduced femtosecond time-resolved polar Kerr rotation ͑fs-TRKR͒ spectroscopy indicate that ferromagnetically-coupled Mn spins are rotated instantaneously by the photogenerated hole spins, and they relax back to the original, in-plane state in tens of picoseconds ͑ps͒ as a result of strong damping. These pictures suggest that the photogenerated hole spins form coupled hole-Mn spin complex, in contrast to the paramagnetic semiconductor systems. 2,3 Ferromagnetic ͑Ga,Mn͒As samples were grown by molecular-beam epitaxy on GaAs/GaAs͑100͒ substrates at the substrate temperature of 250°C. Thickness and Mn contents of two representative samples were 200 nm and x ϭ0.011 ͑Curie temperature T C ϭ30 K), and 100 nm and x ϭ0.068 (T C ϭ90 K), respectively. Hole concentration is inferred to be 10 20 cm Ϫ3 or below for the xϭ0.011 sample and around 10 20 cm Ϫ3 for the xϭ0.068 sample, referring to the existing carrier transport data. 4 Lattice mismatch between the ͑Ga,Mn͒As layers and the substrates yields an in-plane magnetic anisotropy 5 in the present samples.Before excitation, samples are in the virgin state at which magnetization of magnetic domains is primarily in the lateral direction ͓Fig. 1͑a͔͒. Reflecting the hole-mediated ferromagnetism, 6 spin-split density of states ͑DOS͒ of the valence band is expressed by two half parabolas in the spinplane A whose spin quantum axes are along ͉S x,y ;Ϯ1/2͘ ͓Fig. 1͑b͔͒. The magnitude of the splitting is given by the exchange-split energy ⌬E ex . 7 Here, we neglect orbital angular momentum L of holes for simplicity. Linearly polarized probing light reflected normal from the sample surface only exhibits small longitudinal/transverse Kerr rotation. Through the ba...

We have investigated the electronic structure of the p-type diluted magnetic semiconductor In1−xMnxAs by photoemission spectroscopy. The Mn 3d partial density of states is found to be basically similar to that of Ga1−xMnxAs. However, the impurity-band like states near the top of the valence band have not been observed by angle-resolved photoemission spectroscopy unlike Ga1−xMnxAs. This difference would explain the difference in transport, magnetic and optical properties of In1−xMnxAs and Ga1−xMnxAs. The different electronic structures are attributed to the weaker Mn 3d -As 4p hybridization in In1−xMnxAs than in Ga1−xMnxAs.Diluted magnetic semiconductors (DMS) have attracted much attention because of the combination of magnetic and semiconducting properties and hence high potential for new device applications. Recently DMS based on III-V compounds have been extensively studied because of the success in doping high concentrations of transition-metal ions by molecular beam epitaxy (MBE).

We have grown (In y Ga 1-y ) 1-x Mn x As ferromagnetic semiconductor layers with Mn composition x up to 0.13 on InP substrates by molecular beam epitaxy. Near the lattice-matched composition, i.e., y ~ 0.53, the Curie temperature increases linearly with the ferromagnetically effective Mn composition x eff , following the empirical equation. We obtained Curie temperatures above 100 K when x is relatively high () and the hole concentration is in the order of 10 19 cm -3 .