Epitaxial Ferromagnetic MnGa and (MnNi)Ga Thin Films With Perpendicular Magnetization on GaAs
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EPITAXIAL FERROMAGNETIC MnGa AND (MnNi)Ga THIN FILMS WITH PERPENDICULAR MAGNETIZATION ON GaAs M. TANAKAa), J.P. HARBISON, T.D. SANDS, B.A. PHILIPSb), J. DE BOECKC), T.L. CHEEKS, L.T. FLOREZ and V.G. KERAMIDAS Bellcore, 331 Newman Springs Road, Red Bank, NJ 07701-7040. a)On leavefrom Departmentof ElectricalEngineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan. b)Presentaddress:MaterialsScience Department,CarnegieMellon University, Pittsburgh,PA 15213-3890. c)Permanentaddress: InteruniversityMicroelectronicsCenter (IMEC), Kapeldreef75, B3001 Leuven, Belgium. ABSTRACT We have successfully grown thermodynamically stable ferromagnetic MnxGal-x (x--0.55-0.60) thin films with thicknesses ranging from 3 nm to 60 nm on GaAs substrates by molecular beam epitaxy. The c-axis of the tetragonal structure of the MnGa film is shown to be aligned perpendicular to the substrate. Both magnetization measurements and extraordinary Hall effect measurements indicate perpendicular magnetization of the MnGa films, exhibiting squarelike hysteresis characteristics. Furthermore, we have investigated the effect of Ni additions as a substitution for Mn in (Mn6o-yNiy)Ga4o alloy thin films with y=O - 30 at% Ni. With increasing Ni, the perpendicular component of the magnetization becomes smaller up to y=18 where the magnetization is in-plane. At y=30, the magnetization is again perpendicular. INTRODUCTION Epitaxial growth of ferromagnetic thin films on III-V semiconductors can lead to the integration of magnetic effects with high speed III-V electronics/photonics [1], offering a wide range of possibilities for producing new devices such as non-volatile memory coupled with underlying Ill-V circuitry. Although most of the magnetic thin films so far obtained have inplane magnetization due to the shape anisotropy [2], many potential applications of ferromagnetic films require magnetization perpendicular to the substrate, both to allow higher storage density in magnetic storage applications and to allow the use of extraordinary Hall effect (EHE) and magneto-optic Kerr effect (MOKE). Recently, we have explored the growth of metastable rMnAl on GaAs substrates by molecular beam epitaxy (MBE), and found that heteroepitaxy helps to align the magnetization direction of the MnAl film, which lies along the c-axis of the tetragonal unit cell of r phase, in an orientation perpendicular to the substrate [3][4]. In this paper, we present our study of the MBE growth of MnxGalx (x--0.55 - 0.60), the stable ferromagnetic Ga-based phase, compatible with GaAs substrates in epitaxy due to the shared group III atom in the MnGa/GaAs couple. It is shown that the MBE-grown MnGa films indeed have perpendicular magnetization, square-like EHE hysteresis characteristics, and a high value of remanent magnetization, making them a promising candidate for applications in certain non-volatile magnetic memory coupled with III-V optical and/or electronic devices. Furthermore, we have investigated the MBE growth of (Mn60the compositon. alloy films with y--0 -
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