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Spin-dependent tunneling and properties of ferromagnetic (Ga,Mn)As (invited)

We have investigated the magnetic and magnetotransport properties of (Ga, Mn)As/(Al, Ga)As/(Ga, Mn)As semiconductor-based magnetic trilayer structures. We observe a weak ferromagnetic interlayer coupling between the two ferromagnetic (Ga, Mn)As layers as well as magnetoresistance effects due to spin-dependent scattering and to spin-dependent tunneling. Both the coupling strength and the magnetoresistance ratio decrease with the increase of temperature and/or the increase of Al composition of the nonmagnetic (Al, Ga)As layer.

Epitaxial growth and properties of III-V magnetic semiconductor (GaMn)As and its heterostructuresLow-temperature molecular beam epitaxy allows one to dope GaAs with Mn over its solubility limit, making it possible to realize a III-V-based diluted magnetic semiconductor ͑Ga,Mn͒As. Magnetization measurements revealed that ͑Ga,Mn͒As is ferromagnetic at low temperatures. The ferromagnetic transition temperature T c can be as high as 110 K for 5% Mn. Magnetotransport properties of ͑Ga,Mn͒As were found closely related to its magnetic properties. The temperature and magnetic-field B dependence of resistivity can be understood in terms of spin-dependent scattering. The p -d exchange determined from the B dependence of is shown to be consistent with the exchange expected from T c based on the Ruderman-Kittel-Kasuya-Yosida interaction. The anomalous Hall effect dominates the Hall resistance up to room temperature, allowing one to determine the magnetic properties from the magnetotransport measurements alone. Since ͑Ga,Mn͒As can be grown pseudomorphically on GaAs, one can introduce ferromagnetism in GaAs-based heterostructures such as resonant tunneling diodes and observe spin-dependent phenomena in current-voltage characteristics. Magneto-optical properties of ͑Ga,Mn͒As films are also presented.

Magnetic properties of all-semiconductor (Ga,Mn)As/(Al,Ga)As/(Ga,Mn)As trilayer structures are studied. The interactions between the two ferromagnetic (Ga,Mn)As layers are investigated by magnetotransport measurements in a number of samples with different GaAs thickness or with different Al content in the intermediary nonmagnetic (Al,Ga)As layer. The results indicate that carriers present in the nonmagnetic layer mediate the coupling between the two ferromagnetic layers.