Strain-induced high ferromagnetic transition temperature of MnAs epilayer grown on GaAs (110)
- Pengfa Xu^{1},
- Jun Lu^{1},
- Lin Chen^{1},
- Shuai Yan^{1},
- Haijuan Meng^{1},
- Guoqiang Pan^{2} and
- Jianhua Zhao^{1}Email author
https://doi.org/10.1186/1556-276X-6-125
© Xu et al; licensee Springer. 2011
Received: 12 August 2010
Accepted: 9 February 2011
Published: 9 February 2011
Abstract
MnAs films are grown on GaAs surfaces by molecular beam epitaxy. Specular and grazing incidence X-ray diffractions are used to study the influence of different strain states of MnAs/GaAs (110) and MnAs/GaAs (001) on the first-order magnetostructural phase transition. It comes out that the first-order magnetostructural phase transition temperature T _{t}, at which the remnant magnetization becomes zero, is strongly affected by the strain constraint from different oriented GaAs substrates. Our results show an elevated T _{t} of 350 K for MnAs films grown on GaAs (110) surface, which is attributed to the effect of strain constraint from different directions.
PACS: 68.35.Rh, 61.50.Ks, 81.15.Hi, 07.85.Qe
Introduction
Today, there is growing interest for realization of new technologies utilizing spin degree of freedom of electrons in semiconductor devices [1]. The technology of manipulating spin in semiconductors promises devices with enhanced functionality and higher speed. A prerequisite for realization of such kind of devices is development of solid-state spin injectors at room temperature. Diluted magnetic semiconductors (DMSs) and ferromagnet/semiconductor hybrids are two important components for efficient spin injection. The exploitation of DMSs, however, is severely hindered by their low Curie temperature due to the low solubility of transition metals in semiconductors [2, 3]. With room-temperature ferromagnetism and high crystal quality, MnAs has been epitaxied on (001)-, (110)-, (111)-, and (113)-oriented GaAs substrates [4–9]. Moreover, MnAs/GaAs having sharper interface than that of Fe/GaAs has been presented [10, 11]; the sharp interface is considered to be crucial for obtaining higher transmission efficiencies. Recently, spin injection from MnAs into GaAs has been demonstrated [12], and the spin-dependent tunneling experiments show that the spin polarization at MnAs/GaAs interfaces is high [13, 14]. Therefore, MnAs/GaAs hybrid is attracting more and more attention for its potential applications in spin injection, magnetic tunneling junctions, and magnetically logic devices.
The first-order magnetostructural phase transition is a long-standing topic in magnetism [15–20]. Bulk MnAs shows a coupled first-order magnetostructural phase transition from the ferromagnetic hexagonal α-phase (P6(3)/mmc) to the paramagnetic orthorhombic β-phase (Pnma) which is contracted in volume by 2% at about 318 K. For epitaxial MnAs films on GaAs substrate, the transition proceeds continuously over a broad temperature range with coexistence of the two phases. The phase coexistence results in a considerable fraction of MnAs epitaxial films which are usually in paramagnetic phase at ~30°C, a strong limitation for room temperature spintronic devices. The first-order magnetostructural phase transition temperature T _{t}, at which the remnant magnetization becomes zero, can be enhanced either by applying an external magnetic field or by growing MnAs films on different oriented GaAs substrates [21]. For example, T _{t} for MnAs films grown on GaAs (111)B is higher than that grown on GaAs (001) [18, 22, 23].
Epitaxial MnAs films on GaAs (001) and GaAs (111)B have been thoroughly investigated [4–6], while little attention has been paid to MnAs films grown on GaAs (110) [7]. The spin relaxation time is considered crucial important for practical application of spin memory devices or spin quantum computers. In GaAs (110) quantum wells, the spin relaxation time is in nanosecond range, much longer than that in GaAs (001) where the spin relaxation time is in picoseconds range [7]. More work is expected for investigation of MnAs films grown on GaAs (110) surfaces. In this work, we will present that epitaxial MnAs films grown on GaAs (110) are with a different strain states from MnAs films grown on GaAs (001), and α-phase can coexist with β-phase to a higher temperature (remnant magnetization becomes zero when the temperature reaches 350 K).
Experimental procedure
Growth parameters and the thickness for samples A-D
Sample | Growth temperature (°C) | As_{4}/Mn BEP ratio | Furnace cooling | Thickness (nm) | GaAs substrate |
---|---|---|---|---|---|
A | 230 | 300 | N | 11 | GaAs (001) |
B | 210 | 175 | N | 3 | GaAs (110) |
C | 210 | 300 | N | 11 | GaAs (110) |
D | 210 | 175 | Y | 11 | GaAs (110) |
Results and discussion
Lattice parameters, primitive cell volume, and transition temperature of samples A-D and MnAs bulk [27]
MnAs bulk | Sample A | Sample B | Sample C | Sample D | |
---|---|---|---|---|---|
a (Å) | 5.71 | 5.78 | 5.71 | 5.67 | 5.69 |
b (Å) | 3.72 | 3.69 | 3.73 | 3.72 | 3.72 |
c (Å) | 6.45 | 6.41 | 6.43 | 6.45 | 6.45 |
T _{t} (Å) | 313 | 325 | 335 | 350 | 350 |
V (Å^{3}) | 137.06 | 136.71 | 136.95 | 136.05 | 136.53 |
Summary
In summary, we have shown that the ferromagnetic order in MnAs can be extended to higher temperature by growing MnAs on GaAs (110). Ferromagnetic α-phase can coexist with paramagnetic β-phase to 350 K. By XRD measurements, it is found that T _{t} is not a simple function of primitive cell volume, and stretching of lattice parameters in the basal plane or compressing of lattice parameter in the perpendicular direction results in a higher T _{t}. The result described here attests to a strong link between anisotropic strain and epilayer properties. Understanding and mastering these characterizations may open a possibility to control magnetic properties via selection of substrate orientation and provide new possibilities for using MnAs epilayer in spintronic devices.
Declarations
Acknowledgements
This work was supported in part by the National Natural Science Foundation of China under Grant No. 60836002 and the special funds for the Major State Basic Research Contract No. 2007CB924903 of China and the Knowledge Innovation Program Project of Chinese Academy of Sciences No. KJCX2.YW.W09-1.
Authors’ Affiliations
References
- Zhao YJ, Geng WT, Freeman AJ: Structural, electronic, and magnetic properties of α- and β-MnAs: LDA and GGA investigations. Phys Rev B 2002, 65: 113202. 10.1103/PhysRevB.65.113202View ArticleGoogle Scholar
- Bonanni A: Ferromagnetic nitride-based semiconductors doped with transition metals and rare earths. Semicond Sci Technol 2007, 22: R41. 10.1088/0268-1242/22/9/R01View ArticleGoogle Scholar
- Bonanni A, Simbrunner C, Wegscheider M, Przybylinska H, Wolos A, Sitter H, Jantsch W: Doping of GaN with Fe and Mg for spintronics applications. Phys Stat Sol (b) 2006, 243: 1701. 10.1002/pssb.200565230View ArticleGoogle Scholar
- Schippan F, Trampert A, Däweritz L, Ploog KH, Dennis B, Neumann KU, Ziebeck KRA: Microstructure formation during MnAs growth on GaAs(0 0 1). J Cryst Growth 2000, 201/202: 674. 10.1016/S0022-0248(98)01448-1View ArticleGoogle Scholar
- Tanaka M, Saito K, Nishinaga T: Epitaxial MnAs/GaAs/MnAs trilayer magnetic heterostructures. Appl Phys Lett 1999, 74: 64. 10.1063/1.122953View ArticleGoogle Scholar
- Däweritz L, Kästner M, Hesjedal T, Plake T, Jenichen B, Ploog KH: Structural and magnetic order in MnAs films grown by molecular beam epitaxy on GaAs for spin injection. J Cryst Growth 2003, 251: 297.View ArticleGoogle Scholar
- Kolovos-Vellianitis D, Herrmann C, Däweritz L, Ploog KH: Structural and magnetic properties of epitaxially grown MnAs films on GaAs(110). Appl Phys Lett 2005, 87: 092505. 10.1063/1.2035328View ArticleGoogle Scholar
- Akinaga H, Miyanishi S, Tanaka K, Van Roy W, Onodera K: Magneto-optical properties and the potential application of GaAs with magnetic MnAs nanoclusters. Appl Phys Lett 2000, 76: 97. 10.1063/1.125668View ArticleGoogle Scholar
- Akinaga H, De Boeck J, Borghs G, Miyanishi S, Asamitsu A, Van Roy W, Tomioka Y, Kuo LH: Negative magnetoresistance in GaAs with magnetic MnAs nanoclusters. Appl Phys Lett 1998, 72: 3368. 10.1063/1.121606View ArticleGoogle Scholar
- Schippan F, Trampert A, Däweritz L, Ploog KH: Kinetics of MnAs growth on GaAs(001) and interface structure. J Vac Sci Technol B 1999, 17: 1716. 10.1116/1.590814View ArticleGoogle Scholar
- Lu J, Meng HJ, Deng JJ, Xu PF, Chen L, Zhao JH, Jia QJ: Strain and magnetic anisotropy of as-grown and annealed Fe films on c (4 × 4) reconstructed GaAs (001) surface. J Appl Phys 2009, 106: 013911. 10.1063/1.3159642View ArticleGoogle Scholar
- Stephens J, Berezovsky J, McGuire JP, Sham LJ, Gossard AC, Awschalom DD: Spin accumulation in forward-biased MnAs/GaAs schottky diodes. Phys Rev Lett 2004, 93: 097602. 10.1103/PhysRevLett.93.097602View ArticleGoogle Scholar
- Garcia V, Jaffrès H, Eddrief M, Marangolo M, Etgens VH, George JM: Resonant tunneling magnetoresistance in MnAs/III-V/MnAs junctions. Phys Rev B 2005, 72: 081303(R).View ArticleGoogle Scholar
- Garcia V, Jaffrès H, George JM, Marangolo M, Eddrief M, Etgens VH: Spectroscopic measurement of spin-dependent resonant tunneling through a 3D disorder: The case of MnAs/GaAs/MnAs junctions. Phys Rev Lett 2006, 97: 246802. 10.1103/PhysRevLett.97.246802View ArticleGoogle Scholar
- Bean CP, Rodbell DS: Magnetic disorder as a first-order phase transformation. Phys Rev 1962, 126: 104. 10.1103/PhysRev.126.104View ArticleGoogle Scholar
- Menyuk N, Kafalas JA, Dwight K, Goodenough JB: Effects of pressure on the magnetic properties of MnAs. Phys Rev 1969, 177: 942. 10.1103/PhysRev.177.942View ArticleGoogle Scholar
- Zhao YJ, Zunger A: Zinc-blende half-metallic ferromagnets are rarely stabilized by coherent epitaxy. Phys Rev B 2005, 71: 132403. 10.1103/PhysRevB.71.132403View ArticleGoogle Scholar
- Garcia V, Sidis Y, Marangolo M, Vidal F, Eddrief M, Bourges P, Maccherozzi F, Ott F, Panaccione G, Etgens VH: Biaxial strain in the hexagonal plane of MnAs thin films: The key to stabilize ferromagnetism to higher temperature. Phys Rev Lett 2007, 99: 117205. 10.1103/PhysRevLett.99.117205View ArticleGoogle Scholar
- Jenichen B, Kaganer VM, Kästner M, Herrmann C, Däweritz L, Ploog KH, Darowski N, Zizak I: Structural and magnetic phase transition in MnAs(0001)/GaAs(111) epitaxial films. Phys Rev B 2003, 68: 132301. 10.1103/PhysRevB.68.132301View ArticleGoogle Scholar
- Kaganer VM, Jenichen B, Schippan F, Braun W, Däweritz L, Ploog KH: Strain-mediated phase coexistence in MnAs heteroepitaxial films on GaAs: An x-ray diffraction study. Phys Rev B 2002, 66: 045305. 10.1103/PhysRevB.66.045305View ArticleGoogle Scholar
- Ney A, Hesjedal T, Däweritz L, Koch R, Ploog KH: Extending the magnetic order of MnAs films on GaAs to higher temperatures. J Magn Magn Mater 2004, 288: 173. 10.1016/j.jmmm.2004.09.106View ArticleGoogle Scholar
- Das AK, Pampuch C, Ney A, Hesjedal T, Däweritz L, Koch R, Ploog KH: Ferromagnetism of MnAs studied by heteroepitaxial films on GaAs(001). Phys Rev Lett 2003, 91: 087203. 10.1103/PhysRevLett.91.087203View ArticleGoogle Scholar
- Iikawa F, Brasil MJSP, Adriano C, Couto ODD, Giles C, Santos PV, Däweritz L, Rungger I, Sanvito S: Lattice distortion effects on the magnetostructural phase transition of MnAs. Phys Rev Lett 2005, 95: 077203. 10.1103/PhysRevLett.95.077203View ArticleGoogle Scholar
- Rache Salles B, Marangolo M, David C, Girard JC: Cross-sectional magnetic force microscopy of MnAs/GaAs(001). Appl Phys Lett 2010, 96: 052510. 10.1063/1.3309421View ArticleGoogle Scholar
- Däweritz L, Wan L, Jenichen B, Herrmann C, Mohanty J, Trampert A, Ploog KH: Thickness dependence of the magnetic properties of MnAs films on GaAs(001) and GaAs(113)A: Role of a natural array of ferromagnetic stripes. J Appl Phys 2004, 96: 5056.View ArticleGoogle Scholar
- Berry JJ, Potashnik SJ, Chun SH, Ku KC, Schiffer P, Samarth N: Two-carrier transport in epitaxially grown MnAs. Phys Rev B 2001, 64: 052408. 10.1103/PhysRevB.64.052408View ArticleGoogle Scholar
- Willis BTM, Rooksby HP: Magnetic transitions and structural changes in hexagonal manganese compounds. Proc Phys Soc Sect B 1954, 67: 290. 10.1088/0370-1301/67/4/302View ArticleGoogle Scholar
Copyright
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.