Large negative anisotropic magnetoresistance in Co2MnGa Heusler alloy epitaxial thin films

Anisotropic magnetoresistance (AMR) effects in Cox(MnyGa1-y)100-x Heusler alloy thin films epitaxially grown on a MgO single-crystal substrate have been investigated by changing their composition in the ranges of x = 44.4–59.2 at. % and y = 0.44–0.55. Negative AMR ratios were observed at measurement temperatures from 5 to 300 K for all the films, indicating that Co2MnGa films have possible half-metallicity. The AMR ratio changed sensitively depending on the composition of the films. In the case of the film with y = 0.44, the AMR ratio peaked at around x = 50 at. %. In addition, the amplitude of the AMR ratio increased with decreasing y when x was approximately 50 at. %. As a notable result, large negative AMR ratios of −2.32% at 5 K and −0.82% at 300 K, whose amplitude is more than four times that of Co2MnSi films, were obtained for the Co−Mn−Ga films. These results suggest that the Co2MnGa films have a high spin polarization due to half-metallicity.Anisotropic magnetoresistance (AMR) effects in Cox(MnyGa1-y)100-x Heusler alloy thin films epitaxially grown on a MgO single-crystal substrate have been investigated by changing their composition in the ranges of x = 44.4–59.2 at. % and y = 0.44–0.55. Negative AMR ratios were observed at measurement temperatures from 5 to 300 K for all the films, indicating that Co2MnGa films have possible half-metallicity. The AMR ratio changed sensitively depending on the composition of the films. In the case of the film with y = 0.44, the AMR ratio peaked at around x = 50 at. %. In addition, the amplitude of the AMR ratio increased with decreasing y when x was approximately 50 at. %. As a notable result, large negative AMR ratios of −2.32% at 5 K and −0.82% at 300 K, whose amplitude is more than four times that of Co2MnSi films, were obtained for the Co−Mn−Ga films. These results suggest that the Co2MnGa films have a high spin polarization due to half-metallicity.

[1]  C. Palmstrøm,et al.  Low magnetic damping and large negative anisotropic magnetoresistance in half-metallic Co2−xMn1+xSi Heusler alloy films grown by molecular beam epitaxy , 2018, Applied Physics Letters.

[2]  C. Palmstrøm,et al.  Fourfold symmetric anisotropic magnetoresistance in half-metallic Co2MnSi Heusler alloy thin films , 2018 .

[3]  M. Shirai,et al.  Magnetic tunnel junctions with an equiatomic quaternary CoFeMnSi Heusler alloy electrode , 2018 .

[4]  J. A. Logan,et al.  Oxygen migration in epitaxial CoFe/MgO/Co2MnSi magnetic tunnel junctions , 2017 .

[5]  K. Hono,et al.  Enhancement of L21 order and spin-polarization in Co2FeSi thin film by substitution of Fe with Ti , 2017 .

[6]  B. Ruck,et al.  Perpendicular magnetic anisotropy in Co2MnGa and its anomalous Hall effect , 2017 .

[7]  S. Kokado,et al.  Spin polarization ratios of resistivity and density of states estimated from anisotropic magnetoresistance ratio for nearly half-metallic ferromagnets , 2016, 1608.08888.

[8]  Koichiro Inomata,et al.  Chemical ordering and large tunnel magnetoresistance in Co2FeAl/MgAl2O4/Co2FeAl(001) junctions , 2016 .

[9]  T. Sasaki,et al.  Enhancement of magnetoresistance by inserting thin NiAl layers at the interfaces in Co2FeGa0.5Ge0.5/Ag/Co2FeGa0.5Ge0.5 current-perpendicular-to-plane pseudo spin valves , 2016 .

[10]  K. Hono,et al.  Large magnetoresistance in current-perpendicular-to-plane pseudo spin-valves using Co2Fe(Ga0.5Ge0.5) Heusler alloy and AgZn spacer , 2015 .

[11]  S. Kokado,et al.  Twofold and Fourfold Symmetric Anisotropic Magnetoresistance Effect in A Model with Crystal Field , 2015, 1507.05912.

[12]  S. Kokado,et al.  Quantitative analysis of anisotropic magnetoresistance in Co2MnZ and Co2FeZ epitaxial thin films: A facile way to investigate spin-polarization in half-metallic Heusler compounds , 2014 .

[13]  S. Kokado,et al.  Anisotropic magnetoresistance effect of a strong ferromagnet: magnetization direction dependence in a model with crystal field , 2014 .

[14]  B. Hamad.  Investigations of the electronic and magnetic structures of Co2YGa (Y=Cr, Mn) Heusler alloys and their (100) surfaces , 2014 .

[15]  T. Koganezawa,et al.  Structure and magnetoresistance of current-perpendicular-to-plane pseudo spin valves using Co2Mn(Ga0.25Ge0.75) Heusler alloy , 2013 .

[16]  S. Kokado,et al.  Anisotropic Magnetoresistance Effect: General Expression of AMR Ratio and Intuitive Explanation for Sign of AMR Ratio , 2013, 1305.3517.

[17]  B. Johansson,et al.  Magnetic properties and temperature-dependent half-metallicity of Co2Mn(Ga1−xZx) (Z=Si, Ge, Sn) from first-principles calculation , 2013, Journal of physics. Condensed matter : an Institute of Physics journal.

[18]  M. Hayashi,et al.  Spin polarization and Gilbert damping of Co2Fe(GaxGe1−x) Heusler alloys , 2012 .

[19]  S. Kokado,et al.  Anisotropic magnetoresistance in Co 2 (Fe,Mn)Si Heusler epitaxial films: A fingerprint of half-metallicity , 2012 .

[20]  Satoshi Kokado,et al.  Anisotropic Magnetoresistance Effects in Fe, Co, Ni, Fe$_4$N, and Half-Metallic Ferromagnet: A Systematic Analysis , 2011, 1111.4864.

[21]  Yasuo Ando,et al.  Large Magnetoresistance Effect in Epitaxial Co2Fe0.4Mn0.6Si/Ag/Co2Fe0.4Mn0.6Si Devices , 2011 .

[22]  Hong Chen,et al.  Tunable magnetism and half-metallicity in bulk and (1 0 0) surface of quaternary Co2MnGe1−xGax Heusler alloy , 2011 .

[23]  G. Schönhense,et al.  Significant spin polarization of Co2MnGa Heusler thin films on MgO(100) measured by ultraviolet photoemission spectroscopy , 2011 .

[24]  K. Hono,et al.  Large magnetoresistance in current-perpendicular-to-plane pseudospin valve using a Co2Fe(Ge0.5Ga0.5) Heusler alloy , 2011 .

[25]  M. Shirai,et al.  Mechanism of large magnetoresistance in Co 2 MnSi / Ag / Co 2 MnSi devices with current perpendicular to the plane , 2010 .

[26]  C. S. Jacobsen,et al.  Interfacial, electrical, and spin-injection properties of epitaxial Co2MnGa grown on GaAs(100) , 2009 .

[27]  S. Mitani,et al.  Large Interface Spin-Asymmetry and Magnetoresistance in Fully Epitaxial Co2MnSi/Ag/Co2MnSi Current-Perpendicular-to-Plane Magnetoresistive Devices , 2009 .

[28]  K. Hono,et al.  Highly spin-polarized Co 2MnGa 0.5Sn 0.5 Heusler compound , 2009 .

[29]  Nobuki Tezuka,et al.  Improved tunnel magnetoresistance of magnetic tunnel junctions with Heusler Co2FeAl0.5Si0.5 electrodes fabricated by molecular beam epitaxy , 2009 .

[30]  Yasuo Ando,et al.  Large tunnel magnetoresistance in magnetic tunnel junctions using a Co2MnSi Heusler alloy electrode and a MgO barrier , 2008 .

[31]  A. Sakuma,et al.  Magnetic properties, phase stability, electronic structure, and half-metallicity of L 2 1 -type Co 2 ( V 1 − x Mn x ) Ga Heusler alloys , 2008 .

[32]  K. Ishida,et al.  Phase stability of B2 and L21 ordered phases in Co2YGa (Y=Ti, V, Cr, Mn, Fe) alloys , 2007 .

[33]  K. Koepernik,et al.  Spin and orbital magnetism in full Heusler alloys: A density functional theory study of Co 2 Y Z ( Y = Mn , Fe ; Z = Al , Si , Ga , Ge ) , 2006 .

[34]  H. Kubota,et al.  Giant tunneling magnetoresistance in Co2MnSi∕Al–O∕Co2MnSi magnetic tunnel junctions , 2006 .

[35]  Hitoshi Kubota,et al.  Huge Spin-Polarization of L21-Ordered Co2MnSi Epitaxial Heusler Alloy Film , 2005 .

[36]  A. Thomas,et al.  Co2MnSi Heusler alloy as magnetic electrodes in magnetic tunnel junctions , 2004 .

[37]  Yoshio Miura,et al.  Atomic disorder effects on half-metallicity of the full-Heusler alloys Co 2 ( Cr 1 − x Fe x ) Al : A first-principles study , 2004 .

[38]  A. Freeman,et al.  Role of structural defects on the half-metallic character of Co 2 MnGe and Co 2 MnSi Heusler alloys , 2004 .

[39]  M. Pepper,et al.  Cobalt-Based Heusler Alloys for Spin-Injection Devices , 2003 .

[40]  M. Pepper,et al.  Magnetic and electrical properties of Co2MnGa grown on GaAs (001) , 2002 .

[41]  Shoji Ishida,et al.  Search for Half-Metallic Compounds in Co2MnZ (Z=IIIb, IVb, Vb Element) , 1995 .

[42]  K.H.J. Buschow,et al.  New Class of Materials: Half-Metallic Ferromagnets , 1983 .