We present a theory for electronic and magneto-optical properties of n-type In 1Ϫx Mn x As magnetic alloy semiconductors in a high magnetic field Bʈẑ . We use an eight-band Pidgeon-Brown model generalized to include the wave vector (k z ) dependence of the electronic states as well as s-d and p-d exchange interactions with localized Mn d electrons. Calculated conduction-band Landau levels exhibit effective masses and g factors that are strongly dependent on temperature, magnetic field, Mn concentration (x), and k z . Cyclotron resonance ͑CR͒ spectra are computed using Fermi's golden rule and compared with ultrahigh-magnetic-field (Ͼ50 T͒ CR experiments, which show that the electron CR peak position is sensitive to x. Detailed comparison between theory and experiment allowed us to extract the s-d and p-d exchange parameters ␣ and ␤. We find that not only ␣ but also ␤ affects the electron mass because of the strong interband coupling in this narrow-gap semiconductor. In addition, we derive analytical expressions for effective masses and g factors within the eight-band model. Results indicates that (␣Ϫ␤) is the crucial parameter that determines the exchange interaction correction to the cyclotron masses. These findings should be useful for designing novel devices based on ferromagnetic semiconductors.

We have carried out an ultrahigh-field cyclotron resonance study of n-type In 1Ϫx Mn x As films, with Mn composition x ranging from 0% to 12%, grown on GaAs by low-temperature molecular-beam epitaxy. We observe that the electron cyclotron resonance peak shifts to lower field with increasing x. A detailed comparison of experimental results with calculations based on a modified Pidgeon-Brown model allows us to estimate the s-d and p-d exchange-coupling constants, ␣ and ␤, for this important III-V dilute magnetic semiconductor system.

We have carried out an ultrahigh-field cyclotron resonance study of p-type In1−xMnxAs films, with Mn composition x ranging from 0% to 2.5%, grown on GaAs by low-temperature molecularbeam epitaxy. Pulsed magnetic fields up to 500 T were used to make cyclotron resonance observable in these low-mobility samples. The clear observation of hole cyclotron resonance is direct evidence of the existence of a large number of itinerant, effective-mass-type holes rather than localized dlike holes. It further suggests that the p-d exchange mechanism is more favorable than the double exchange mechanism in this narrow gap InAs-based dilute magnetic semiconductor. In addition to the fundamental heavy-hole and light-hole cyclotron resonance absorption appearing near the high-magnetic-field quantum limit, we observed many inter-Landau-level absorption bands whose transition probabilities are strongly dependent on the sense of circular polarization of the incident light.

Submicron ferromagnets have been successfully incorporated into semi-insulating (001) GaAs crystals by Mn+ ion implantation and subsequent rapid annealing. Magnetization measurements reveal room-temperature ferromagnetism. The structural and compositional properties of crystallites have been analyzed by transmission electron microscopy, energy dispersion x-ray spectrum, and electron microdiffraction. The results show that crystallites of MnGa and MnAs with a small amount of Ga are formed. Atomic force microscopy and magnetic force microscopy images indicate that the single-domain magnetic state is dominant in submicron ferromagnets under our annealing conditions (750 °C–900 °C).

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