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Materials with large perpendicular magnetic anisotropies (PMAs) have drawn great attention because of their potential applications in advanced spintronic devices such as spin-transfer-torque magnetic random access memory (STT-MRAM) and ultrahigh-density perpendicular magnetic recording. To date, a large variety of PMA materials have been investigated, such as L10-ordered FePt, CoPt granular films, Co/(Pt,Pd,Ni) multilayers, ultra-thin CoFeB alloys and perpendicularly magnetized Co2FeAl films. Among the various kinds of materials with PMA, MnGa film with L10-structure has received the most attention because it has large PMA (Ku～107 erg/cm3), ultralow Gilbert damping constant (0.008) and theoretically predicted high spin polarization (more than 70%). All these properties make L10-ordered MnGa a good candidate for spintronic devices such as STT-MRAM and spin-torque oscillators. Meanwhile, from the viewpoint of STT related spintronic device, it is necessary to fabricate ultrathin perpendicularly magnetized L10-MnxGa films to lower the critical current for magnetization reversal. However, up to now, in the main researches the ultrathin L10-MnxGa films have been grown on MgO substrates, which makes it difficult to integrate the MnGa-based magnetic tunnel junctions into the semiconductor manufacturing process.In this work, ultrathin L10-Mn1.67Ga films with different thickness values (1-5 nm) are grown on traditional GaAa (001) substrates by a molecule-beam epitaxy system. During the deposition, in situ streaky surface reconstruction patterns are observed from reflection high-energy electron diffraction, which implies high crystalline quality of the L10-Mn1.67Ga film. Only MnGa superlattice (001) and MnGa fundamental (002) peaks can be observed in the X-ray diffraction patterns in a range from 20 to 70, which means that the L10-Mn1.67Ga film is a good single-crystalline with c-axis along the normal direction. The magnetic properties of these films are measured by superconductor quantum interference device magnetometer in a field range of 5 T. The perpendicular M-H curves are almost square, while the in-plane curves are nearly hysteresis-free, each with a remnant magnetization (Mr) of around zero, which clearly evidences the PMA of the ultrathin L10-Mn1.67Ga film. Moreover, as the thickness of L10-Mn1.67Ga film decreases from 5 nm to 1 nm, the ratio of Mr/Ms also decreases from 1 to 0.72, which indicates that the PMA loses as thickness decreases. We also estimate the perpendicular anisotropy constant (Ku) from the relation Ku=Keff+2 Ms2, and the maximum Ku of 14.7 Merg/cm3 is obtained for the 5 nm MnGa film. Although the Ku decreases with thickness decreasing, a Ku value of 8.58 Merg/cm3 is observed in a 2 nm thick film. The obtained results are important for developing the L10-MnGa-based spin-transfer torque Gbit class magnetic random access memory.
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Keywords:
- molecular-beam epitaxy /
- spintronics /
- magnetic anisotropy /
- ultrathin films
[1] Nie S H, Zhu L J, Pan D, Lu J, Zhao J H 2013 Acta Phys. Sin. 62 178103 (in Chinese) [聂帅华, 朱礼军, 潘东, 鲁军, 赵建华 2013 62 178103]
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[3] Mizukami S, Kubota T, Wu F, Zhang X, Miyazaki T, Naganuma H, Oogane M, Sakuma A, Ando Y 2012 Phys. Rev. B 85 014416
[4] Zhu Y, Cai J W 2005 Acta Phys. Sin. 54 393 (in Chinese) [竺云, 蔡建旺 2005 54 393]
[5] Balke B, Fecher G H, Winterlik J, Felser C 2007 Appl. Phys. Lett. 90 152504
[6] Zhu L J, Nie S H, Meng K K, Pan D, Zhao J H, Zheng H Z 2012 Adv. Mater. 24 4547
[7] Wu F, Mizukami S, Watanabe D, Naganuma H, Oogane M, Ando Y, Miyazaki T 2009 Appl. Phys. Lett. 94 122503
[8] Mizukami S, Wu F, Sakuma A, Walowski J, Watanabe D, Kubota T, Zhang X, Naganuma H, Oogane M, Ando Y, Miyazaki T 2011 Phys. Rev. Lett. 106 117201
[9] Winterlik J, Balke B, Fecher G H, Felser C, Alves M C M, Bernardi F, Morais J 2008 Phys. Rev. B 77 054406
[10] Bai Z Q, Cai Y Q, Shen L, Yang M, Ko V, Han G C, Feng Y P 2012 Appl. Phys. Lett. 100 022408
[11] Datta S, Das B 1990 Appl. Phys. Lett. 56 665
[12] Hyun Cheol Koo J H K, Eom J, Chang J, Han S H, Johnson M 2009 Science 325 1515
[13] Jrg Wunderlich B G P, Irvine A C, Zarbo L P, Rozkotov E, Nemec P, Novk V, Sinova J, Jungwirth T 2010 Science 330 1801
[14] Kohda M, Kita T, Ohno Y, Matsukura F, Ohno H 2006 Appl. Phys. Lett. 89 012103
[15] Ohno Y, Young D K, Beschoten B, Matsukura F, Ohno H, Awschalom D D 1999 Nature 402 790
[16] Lou X H, Ademann C, Crooker S A, Garlid E S, Zhang J J, Madhukar Reddy K S, Flexner S D, Palmstrm C J, Crowell P A 2007 Nature Phys. 3 197
[17] Ma Q L, Mizukami S, Kubota T, Zhang X M, Ando Y, Miyazaki T 2014 Phys. Rev. Lett. 112 157202
[18] Mangin S, Ravelosona D, Katine J A, Carey M J, Terris B D, Fullerton E E 2006 Nature Mater. 5 210
[19] Ikeda S, Miura K, Yamamoto H, Mizunuma K, Gan H D, Endo M, Kanai S, Hayakawa J, Matsukura F, Ohno H 2010 Nature Mater. 9 721
[20] Mancoff F B, Dunn J H, Clemens B M, White R L 2000 Appl. Phys. Lett. 77 1879
[21] Houssameddine D, Ebels U, Delaet B, Rodmacq B, Firastrau I, Ponthenier F, Brunet M, Thirion C, Michel J P, Prejbeanu-Buda L, Cyrille M C, Redon O, Dieny B 2007 Nature Mater. 6 441
[22] Sun J Z 2000 Phys. Rev. B 62 570
[23] Krishnan K M 1992 Appl. Phys. Lett. 61 2365
[24] Wu F, Mizukami S, Watanabe D, Sajitha E P, Naganuma H, Oogane M, Ando Y, Miyazaki T 2010 IEEE Trans. Magn. 46 1863
[25] Khler A, Knez I, Ebke D, Felser C, Parkin S S P 2013 Appl. Phys. Lett. 103 162406
[26] Zheng Y H, Han G C, Lu H, Teo K L 2014 J. Appl. Phys. 115 043902
[27] Suzuki K Z, Ranjbar R, Sugihara A, Miyazaki T, Mizukami S 2016 Jpn. J. Appl. Phys. 55 010305
[28] Tanaka M, Harbison J P, Sands T, Philips B, Cheeks T L, de Boeck J, Florez L T, Keramidas V G 1993 Appl. Phys. Lett. 63 696
[29] Huh Y, Kharel P, Shah V R, Li X Z, Skomski R, Sellmyer D J 2013 J. Appl. Phys. 114 013906
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[1] Nie S H, Zhu L J, Pan D, Lu J, Zhao J H 2013 Acta Phys. Sin. 62 178103 (in Chinese) [聂帅华, 朱礼军, 潘东, 鲁军, 赵建华 2013 62 178103]
[2] Wang H, Yang F J, Xue S X, Cao X, Wang J A, Gu H S, Zhao Z Q 2005 Acta Phys. Sin. 54 1415 (in Chinese) [王浩, 杨傅军, 薛双喜, 曹歆, 王君安, 顾豪爽, 赵子强 2005 54 1415]
[3] Mizukami S, Kubota T, Wu F, Zhang X, Miyazaki T, Naganuma H, Oogane M, Sakuma A, Ando Y 2012 Phys. Rev. B 85 014416
[4] Zhu Y, Cai J W 2005 Acta Phys. Sin. 54 393 (in Chinese) [竺云, 蔡建旺 2005 54 393]
[5] Balke B, Fecher G H, Winterlik J, Felser C 2007 Appl. Phys. Lett. 90 152504
[6] Zhu L J, Nie S H, Meng K K, Pan D, Zhao J H, Zheng H Z 2012 Adv. Mater. 24 4547
[7] Wu F, Mizukami S, Watanabe D, Naganuma H, Oogane M, Ando Y, Miyazaki T 2009 Appl. Phys. Lett. 94 122503
[8] Mizukami S, Wu F, Sakuma A, Walowski J, Watanabe D, Kubota T, Zhang X, Naganuma H, Oogane M, Ando Y, Miyazaki T 2011 Phys. Rev. Lett. 106 117201
[9] Winterlik J, Balke B, Fecher G H, Felser C, Alves M C M, Bernardi F, Morais J 2008 Phys. Rev. B 77 054406
[10] Bai Z Q, Cai Y Q, Shen L, Yang M, Ko V, Han G C, Feng Y P 2012 Appl. Phys. Lett. 100 022408
[11] Datta S, Das B 1990 Appl. Phys. Lett. 56 665
[12] Hyun Cheol Koo J H K, Eom J, Chang J, Han S H, Johnson M 2009 Science 325 1515
[13] Jrg Wunderlich B G P, Irvine A C, Zarbo L P, Rozkotov E, Nemec P, Novk V, Sinova J, Jungwirth T 2010 Science 330 1801
[14] Kohda M, Kita T, Ohno Y, Matsukura F, Ohno H 2006 Appl. Phys. Lett. 89 012103
[15] Ohno Y, Young D K, Beschoten B, Matsukura F, Ohno H, Awschalom D D 1999 Nature 402 790
[16] Lou X H, Ademann C, Crooker S A, Garlid E S, Zhang J J, Madhukar Reddy K S, Flexner S D, Palmstrm C J, Crowell P A 2007 Nature Phys. 3 197
[17] Ma Q L, Mizukami S, Kubota T, Zhang X M, Ando Y, Miyazaki T 2014 Phys. Rev. Lett. 112 157202
[18] Mangin S, Ravelosona D, Katine J A, Carey M J, Terris B D, Fullerton E E 2006 Nature Mater. 5 210
[19] Ikeda S, Miura K, Yamamoto H, Mizunuma K, Gan H D, Endo M, Kanai S, Hayakawa J, Matsukura F, Ohno H 2010 Nature Mater. 9 721
[20] Mancoff F B, Dunn J H, Clemens B M, White R L 2000 Appl. Phys. Lett. 77 1879
[21] Houssameddine D, Ebels U, Delaet B, Rodmacq B, Firastrau I, Ponthenier F, Brunet M, Thirion C, Michel J P, Prejbeanu-Buda L, Cyrille M C, Redon O, Dieny B 2007 Nature Mater. 6 441
[22] Sun J Z 2000 Phys. Rev. B 62 570
[23] Krishnan K M 1992 Appl. Phys. Lett. 61 2365
[24] Wu F, Mizukami S, Watanabe D, Sajitha E P, Naganuma H, Oogane M, Ando Y, Miyazaki T 2010 IEEE Trans. Magn. 46 1863
[25] Khler A, Knez I, Ebke D, Felser C, Parkin S S P 2013 Appl. Phys. Lett. 103 162406
[26] Zheng Y H, Han G C, Lu H, Teo K L 2014 J. Appl. Phys. 115 043902
[27] Suzuki K Z, Ranjbar R, Sugihara A, Miyazaki T, Mizukami S 2016 Jpn. J. Appl. Phys. 55 010305
[28] Tanaka M, Harbison J P, Sands T, Philips B, Cheeks T L, de Boeck J, Florez L T, Keramidas V G 1993 Appl. Phys. Lett. 63 696
[29] Huh Y, Kharel P, Shah V R, Li X Z, Skomski R, Sellmyer D J 2013 J. Appl. Phys. 114 013906
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