Off-stoichiometric full-Heusler alloy Co_2 MnAl thin films with different thicknesses are epitaxially grown on GaAs(001) substrates by molecular-beam epitaxy. The composition of the films, close to Co_(1.65)Mn_(1.35)A...Off-stoichiometric full-Heusler alloy Co_2 MnAl thin films with different thicknesses are epitaxially grown on GaAs(001) substrates by molecular-beam epitaxy. The composition of the films, close to Co_(1.65)Mn_(1.35)Al(CMA),is determined by x-ray photoelectron spectroscopy and energy dispersive spectroscopy. Tunable perpendicular magnetic anisotropy(PMA) from 3.41 Merg/cm^3 to 1.88 Merg/cm^3 with the thickness increasing from 10 nm to 30 nm is found,attributed to the relaxation of residual compressive strain. Moreover, comparing with the ultrathin CoFeB/MgO used in the conventional perpendicular magnetic tunnel junction, the CMA electrode has a higher magnetic thermal stability with more volume involved. The PMA in CMA films is sustainable up to 300℃,compatible with semiconductor techniques. This work provides a possibility for the development of perpendicular magnetized full-Heusler compounds with high thermal stability and spin polarization.展开更多
An unprecedentedly short milling time of 30 s was applied to gas-atomized MnAl powder in order to develop permanent magnet properties and,in particular,coercivity.It is shown that such a short processing time followed...An unprecedentedly short milling time of 30 s was applied to gas-atomized MnAl powder in order to develop permanent magnet properties and,in particular,coercivity.It is shown that such a short processing time followed by annealing results in efficient nanostructuring and controlled phase transformation.The defects resulting from the microstrain induced during milling,together with the creation of the bphase during post-annealing,act as pinning centers resulting in an enhanced coercivity.This study shows the importance of finding a balance between the formation of the ferromagnetic s-MnAl phase and the bphase in order to establish a compromise between magnetization and coercivity.A coercivity as high as 4.2 kOe(1 Oe=79.6 A·m^-1)was obtained after milling(30 s)and annealing,which is comparable to values previously reported in the literature for milling times exceeding 20 h.This reduction of the postannealing temperature by 75℃ for the as-milled powder and a 2.5-fold increase in coercivity,while maintaining practically unchanged the remanence of the annealed gas-atomized material,opens a new path for the synthesis of isotropic MnAl-based powder.展开更多
Electric luminescence and its circular polarization in a Co2 MnAl injector-based light emitting diode （LED） has been detected at the transition of e–A0 C , where injected spin-polarized electrons recombine with bou...Electric luminescence and its circular polarization in a Co2 MnAl injector-based light emitting diode （LED） has been detected at the transition of e–A0 C , where injected spin-polarized electrons recombine with bound holes at carbon acceptors. A spin polarization degree of 24.6% is obtained at 77 K after spin-polarized electrons traverse a distance of 300 nm before they recombine with holes bound at neutral carbon acceptors in a p ＋ -GaAs layer. The large volume of the p ＋ -GaAs layer can facilitate the detection of weak electric luminescence （EL） from e–A 0C emission without being quenched at higher bias as in quantum wells. Moreover, unlike the interband electric luminescence in the p＋ -GaAs layer, where the spin polarization of injected electrons is destroyed by a very effective electron–hole exchange scattering （BAP mechanism）, the spin polarization of injected electrons seems to survive during their recombination with holes bound at carbon acceptors.展开更多
Thin Mn（2 nm）/Al（2 nm） bilayers serving as buffer layers have been prepared prior to the deposition of MnAl films. The ferromagnetic T-phase forms in the buffer layers at an optimum substrate temperature. As a tem...Thin Mn（2 nm）/Al（2 nm） bilayers serving as buffer layers have been prepared prior to the deposition of MnAl films. The ferromagnetic T-phase forms in the buffer layers at an optimum substrate temperature. As a template it induces the growth of following MnAl film. Compared with the case of film without buffer layer, the growth of nonferromagnetic phase is suppressed and the structural and magnetic properties of MnAl film are improved. Weak dipolar inter-grain coupling is revealed in the MnAl film, and the magnetic reversal process is dominated by magnetic moment rotation.展开更多
The effect of Zn substitution on the structure and magnetic properties of τ-MnAl has been investigated sys-tematically. It is found that Zn substitution can stabilize the structure of τ-phase and thus a significant ...The effect of Zn substitution on the structure and magnetic properties of τ-MnAl has been investigated sys-tematically. It is found that Zn substitution can stabilize the structure of τ-phase and thus a significant amount of τ-phase can be produced. Zn increases the coercivity and saturation magnetization of the τ-MnAl but reduces the Currie temperature. However, excess Zn is detrimental to the magnetic parameters. The optimum magnetic performance was found in samples with Zn substitution to 2.9% Mn atoms and 3.5% Al atoms, respectively.展开更多
采用高能球磨和热处理工艺制备了MnAl合金粉体,使用SEM、XRD和网络矢量分析仪研究Al含量对MnAl合金粉体组织结构和微波吸收特性的影响。结果表明:随Al含量的增加,MnAl合金粉体中Al0.89Mn1.11、β-Mn和Al2Mn3含量降低、Al8Mn5含量升高,...采用高能球磨和热处理工艺制备了MnAl合金粉体,使用SEM、XRD和网络矢量分析仪研究Al含量对MnAl合金粉体组织结构和微波吸收特性的影响。结果表明:随Al含量的增加,MnAl合金粉体中Al0.89Mn1.11、β-Mn和Al2Mn3含量降低、Al8Mn5含量升高,使粉体磁损耗和介电损耗增加、共振频率向低频移动、吸收峰数增加。吸波层厚度为2.0mm时,Mn40Al60样品在12.2 GHz频率处有最大吸收峰,其反射率最小值为–26.5 d B,具有较好的频宽效果。MnAl粉体对电磁波的吸波机理包括吸波涂层内的损耗以及前后界面反射电磁波在前界面处的干涉损耗。展开更多
采用真空悬浮熔炼和高能球磨工艺制备Al8Mn5合金粉体,使用XRD和网络矢量分析仪研究回火温度对粉体组织结构和微波吸收特性的影响。结果表明:低于或等于400℃回火处理的高能球磨Al8Mn5合金粉体主要由Al8Mn5单相组成,600℃回火处理后,粉...采用真空悬浮熔炼和高能球磨工艺制备Al8Mn5合金粉体,使用XRD和网络矢量分析仪研究回火温度对粉体组织结构和微波吸收特性的影响。结果表明:低于或等于400℃回火处理的高能球磨Al8Mn5合金粉体主要由Al8Mn5单相组成,600℃回火处理后,粉体主要由Al8Mn5、Al2Mn3和Mn2O3相组成;随回火温度升高,Al8Mn5粉体电磁参数虚部的共振频率、损耗因子的峰值频率和吸收峰频率均向高频方向移动;400℃回火粉体具有最强的吸波能力,涂层厚度为2.0 mm时,其反射率最小值达到-37 d B。展开更多
基金Supported by the National Key Research and Development Program of China under Grant Nos 2017YFB0405701 and2018YFB0407601the National Natural Science Foundation of China under Grant Nos U1632264 and 11874349the Key Research Project of Frontier Science of the Chinese Academy of Sciences under Grant Nos QYZDY-SSW-JSC015 and XDPB12
文摘Off-stoichiometric full-Heusler alloy Co_2 MnAl thin films with different thicknesses are epitaxially grown on GaAs(001) substrates by molecular-beam epitaxy. The composition of the films, close to Co_(1.65)Mn_(1.35)Al(CMA),is determined by x-ray photoelectron spectroscopy and energy dispersive spectroscopy. Tunable perpendicular magnetic anisotropy(PMA) from 3.41 Merg/cm^3 to 1.88 Merg/cm^3 with the thickness increasing from 10 nm to 30 nm is found,attributed to the relaxation of residual compressive strain. Moreover, comparing with the ultrathin CoFeB/MgO used in the conventional perpendicular magnetic tunnel junction, the CMA electrode has a higher magnetic thermal stability with more volume involved. The PMA in CMA films is sustainable up to 300℃,compatible with semiconductor techniques. This work provides a possibility for the development of perpendicular magnetized full-Heusler compounds with high thermal stability and spin polarization.
基金financial support from MINECO through NEXMAG(M-era.Net,PCIN-2015-126)and 3D-MAGNETOH(MAT2017-89960-R)projectsfrom the Regional Government of Madrid through the NANOMAGCOST(P2018/NMT-4321)projectIMDEA Nanociencia is supported by the"Severo Ochoa"Programme for Centres of Excellence in R&D,MINECO(SEV-2016-0686).
文摘An unprecedentedly short milling time of 30 s was applied to gas-atomized MnAl powder in order to develop permanent magnet properties and,in particular,coercivity.It is shown that such a short processing time followed by annealing results in efficient nanostructuring and controlled phase transformation.The defects resulting from the microstrain induced during milling,together with the creation of the bphase during post-annealing,act as pinning centers resulting in an enhanced coercivity.This study shows the importance of finding a balance between the formation of the ferromagnetic s-MnAl phase and the bphase in order to establish a compromise between magnetization and coercivity.A coercivity as high as 4.2 kOe(1 Oe=79.6 A·m^-1)was obtained after milling(30 s)and annealing,which is comparable to values previously reported in the literature for milling times exceeding 20 h.This reduction of the postannealing temperature by 75℃ for the as-milled powder and a 2.5-fold increase in coercivity,while maintaining practically unchanged the remanence of the annealed gas-atomized material,opens a new path for the synthesis of isotropic MnAl-based powder.
基金Project supported by the National Basic Research Program of China (Grant No. 2011CB932901)the National Natural Science Foundation of China (GrantNo. 60836002)
文摘Electric luminescence and its circular polarization in a Co2 MnAl injector-based light emitting diode （LED） has been detected at the transition of e–A0 C , where injected spin-polarized electrons recombine with bound holes at carbon acceptors. A spin polarization degree of 24.6% is obtained at 77 K after spin-polarized electrons traverse a distance of 300 nm before they recombine with holes bound at neutral carbon acceptors in a p ＋ -GaAs layer. The large volume of the p ＋ -GaAs layer can facilitate the detection of weak electric luminescence （EL） from e–A 0C emission without being quenched at higher bias as in quantum wells. Moreover, unlike the interband electric luminescence in the p＋ -GaAs layer, where the spin polarization of injected electrons is destroyed by a very effective electron–hole exchange scattering （BAP mechanism）, the spin polarization of injected electrons seems to survive during their recombination with holes bound at carbon acceptors.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60490290, 60678008, 10604016, 50771032,and 50771033)the National Basic Research Program of China (Grant No. 2009CB929201)
文摘Thin Mn（2 nm）/Al（2 nm） bilayers serving as buffer layers have been prepared prior to the deposition of MnAl films. The ferromagnetic T-phase forms in the buffer layers at an optimum substrate temperature. As a template it induces the growth of following MnAl film. Compared with the case of film without buffer layer, the growth of nonferromagnetic phase is suppressed and the structural and magnetic properties of MnAl film are improved. Weak dipolar inter-grain coupling is revealed in the MnAl film, and the magnetic reversal process is dominated by magnetic moment rotation.
文摘The effect of Zn substitution on the structure and magnetic properties of τ-MnAl has been investigated sys-tematically. It is found that Zn substitution can stabilize the structure of τ-phase and thus a significant amount of τ-phase can be produced. Zn increases the coercivity and saturation magnetization of the τ-MnAl but reduces the Currie temperature. However, excess Zn is detrimental to the magnetic parameters. The optimum magnetic performance was found in samples with Zn substitution to 2.9% Mn atoms and 3.5% Al atoms, respectively.
文摘采用高能球磨和热处理工艺制备了MnAl合金粉体,使用SEM、XRD和网络矢量分析仪研究Al含量对MnAl合金粉体组织结构和微波吸收特性的影响。结果表明:随Al含量的增加,MnAl合金粉体中Al0.89Mn1.11、β-Mn和Al2Mn3含量降低、Al8Mn5含量升高,使粉体磁损耗和介电损耗增加、共振频率向低频移动、吸收峰数增加。吸波层厚度为2.0mm时,Mn40Al60样品在12.2 GHz频率处有最大吸收峰,其反射率最小值为–26.5 d B,具有较好的频宽效果。MnAl粉体对电磁波的吸波机理包括吸波涂层内的损耗以及前后界面反射电磁波在前界面处的干涉损耗。
文摘采用真空悬浮熔炼和高能球磨工艺制备Al8Mn5合金粉体,使用XRD和网络矢量分析仪研究回火温度对粉体组织结构和微波吸收特性的影响。结果表明:低于或等于400℃回火处理的高能球磨Al8Mn5合金粉体主要由Al8Mn5单相组成,600℃回火处理后,粉体主要由Al8Mn5、Al2Mn3和Mn2O3相组成;随回火温度升高,Al8Mn5粉体电磁参数虚部的共振频率、损耗因子的峰值频率和吸收峰频率均向高频方向移动;400℃回火粉体具有最强的吸波能力,涂层厚度为2.0 mm时,其反射率最小值达到-37 d B。
