Ultrathin multilayer of Fe and Ge: structure and magnetic properties

Metal-semiconductor multilayers are interesting, artificial structures as prospective candidates for spin injection devices. A Fe–Ge multilayer sample with very thin individual layers (few crystallographic planes) has been deposited by sputtering on Si[1 0 0] substrate. We have characterized the structure of this multilayer sample using X-ray diffraction, X-ray reflectometry and neutron reflectometry. The magnetic moment density in the ferromagnetic Fe layer has been obtained by polarized neutron reflectometry and the bulk magnetic behavior of the thin film by SQUID magnetometer measurements. We found that the film is a soft ferromagnet at room temperature with a substantially reduced magnetic moment of the Fe atoms.     

X光激发氮氧化铝膜层电子特征能量探测与分析

本文报告了用Ｘ光电子能谱法（ＸＰＳ）对氮氧化铝／铁膜内层电子特征能量的探测与分析,获得了膜层中不同深度的元素成分及化学结构．结果表明：ＸＰＳ方法是研究氮氧化铝选择性吸收膜的有效方法．     

Kinetic arrest of the first-order to R3c Pbnm phase transition in supercooled La(x)MnO(3+δ) (x = 1 and 0.9)

We report the occurrence of kinetic arrest of the first-order phase transition from R3c to Pbnm in supercooled La(x)MnO(3±δ) (x = 1 and 0.9, i.e. δ > 0.125). Structural studies have been done, employing low temperature transmission electron microscopy (LT-TEM) and low temperature x-ray diffraction (LT-XRD) techniques. No phase transformation was observed even in La(x)MnO(3±δ) aged for ~12 h at 98 K. The evidence of the occurrence of kinetic arrest was realized at low temperatures through in situ electron beam triggered nucleation and perpetual devitrification of the R3c phase into a Pbnm phase. It was clearly evidenced that the R3c structure of La(x)MnO(3±δ), below its ferromagnetic transition temperature, is metastable and prone to be transformed to a Pbnm orthorhombic structure following initiation by an electron beam trigger. The electron beam transformed Pbnm phase was found to transform back to the R3c phase through a first-order phase transition occurring close to the ferromagnetic to paramagnetic transition (T(c)) during heating. The glass-like kinetics of the arrested R3c phase has been investigated through resistance relaxation measurements, showing a decreasing logarithmic rate of decay of the arrested R3c phase towards the stable Pbnm phase with decreasing temperature, down to 5 K. On the basis of the correlations observed in the resistance-versus-temperature, magnetization-versus-temperature, magnetization-versus-field, resistance relaxation and LT-XRD measurements, the occurrence of kinetic arrest has been attributed to the suppression of Jahn-Teller distortion by double exchange across the insulator-metal transition.     

超薄Fe(4(A))膜磁特性极化中子反射研究

利用分子束外延薄膜生长技术,制备了200 (A)V/4 (A) Fe/900 V/MgO(100)薄膜样品,通过X射线反射和极化中子反射两种测量手段获得了薄膜的表面、界面及各层膜厚的相关结构信息.中子反射结果表明,Fe原子磁矩在室温下约为1.0±0.1μB,随着温度的降低,Fe原子磁矩增加,在10 K时达到1.5±0.1μB.利用指数定律拟合磁矩随温度的变化情况,外推得出4(A)铁薄膜样品的居里温度约为310±30 K.

Abstract：

Uhrathin Fe film 200 (A)V/4 (A)Fe/900 (A)V/MgO(100) has been prepared by molecular beam epitaxy (MBE). The structure parameters, such as the surface and interface roughness and the thickness of each layer, were obtained by X-ray and neutron reflectivity measurement. The magnetic properties of the thin Fe layer were investigated by polarized neutron reflectometry at different temperature. The result shows that the magnetic moment of an Fe atom is about 1.0 ± 0.1 μB at room temperature and increases to 1.5 ±0.1 μBat 10 K. The Curie temperature of the thin Fe film is estimated to be 310 ± 30 K.     

Reconstruction control of magnetic properties during epitaxial growth of ferromagnetic Mn3-deltaGa on Wurtzite GaN(0001)

Binary ferromagnetic Mn(3-delta)Ga (1.2<3-delta< or =1.5) crystalline thin films have been epitaxially grown on wurtzite GaN(0001) surfaces using rf N-plasma molecular beam epitaxy. The film structure is face-centered tetragonal with CuAu type-I (L1(0)) ordering with (111) orientation. The in-plane epitaxial relationship to GaN is nearly ideal with [110](MnGa) parallel[1100](GaN) and [112](MnGa) parallel[1120](GaN). We observe magnetic anisotropy along both the in-plane and out-of-plane directions. The magnetic moments are found to depend on the Mn/(Mn+Ga) flux ratio and can be controlled by observation of the surface reconstruction during growth, which varies from 1x1 to 2x2 with increasing Mn stoichiometry.     

Nanoscale magnetic structure of ferromagnet/antiferromagnet manganite multilayers

We use polarized neutron reflectometry and dc magnetometry to obtain a comprehensive picture of the magnetic structure of a series of La(2/3)Sr(1/3)MnO3/Pr(2/3)Ca(1/3)MnO3 (LSMO/PCMO) superlattices, with varying thickness of the antiferromagnetic (AFM) PCMO layers (0相似文献   

Observation of magnetic ripple and nanowidth domains in a layered ferromagnet

We investigated ferromagnetic domain structures on nanometer to micrometer scale for single crystals of a layered ferromagnet, La(2-2x)Sr(1+2x)Mn2O7 (0.32 < or = x < or = 0.40), as functions of x and temperature by means of Lorentz electron microscopy. We have succeeded in observing the evolution of magnetic ripple structure, dynamically, related to a spin reorientation transition where the magnetization direction switches between parallel and perpendicular to the layers. Our high-resolution magnetic domain imaging revealed that the ripple state is characterized by the evolution of magnetic nanowidth domains.     

Cation Radii and Oxygen Deficiency Effects on the Structural,Magnetic, and Electrical Properties in La 1− x Sr x MnO 3−δ □ δ Manganites ( x = 0.2-0.5 and δ = 0.1)

The series of non-stochiometric strontium substituted lanthanium manganites La 1 m x Sr x MnO 3 m i i ( i = 0.1, x = 0.2-0.5) has been studied and show the effect of oxygen deficiency on the structural transition, magnetic and electrical properties of these compounds. Polycrystalline samples La 1 m x Sr x MnO 3 m i i were synthesised by a new method at atmospheric pressure. In this series of manganites, the Mn 4+ content is systematically decreased due to increase in the non-stoichiometry. X-ray diffraction analysis shows a phase transition from orthorhombic to rhombohedral systems for 0.2 h x h 0.5. The material is ferromagnetic for 0.3 h x h 0.5 and antiferromagnetic for x = 0.2. The Curie temperature T C increases with increasing x . The resistivity as a function of temperature shows that samples with x = 0.3 and ferromagnetic metal between T CF and T P becomes ferromagnetic insulators below T CF where charge-ordering seems to appear.     

Interface coupling transition in a thin epitaxial antiferromagnetic film interacting with a ferromagnetic substrate

We report experimental evidence for a transition in the interface coupling between an antiferromagnetic film and a ferromagnetic substrate. The transition is observed in a thin epitaxial NiO film grown on top of Fe(001) as the film thickness is increased. Photoemission electron microscopy excited with linearly polarized x rays shows that the NiO film is antiferromagnetic at room temperature with in-plane uniaxial magnetic anisotropy. The anisotropy axis is perpendicular to the Fe substrate magnetization when the NiO thickness is less than about 15 A, but rapidly becomes parallel to the Fe magnetization for a NiO coverage higher than 25 A.     

Cu掺杂LaMn1－xCuxO3体系的磁转变和导电行为研究

系统研究了LaMn_1-xCu_xO₃(x=0.05，0.10，0.20，0.30，0.40)体系的磁转变和导电行为.结果表明，在LaMnO₃反铁磁母体中掺杂极少量的Cu(x=0.05)使该体系在157K左右出现强的铁磁转变，随着Cu掺杂浓度的增加，居里温度逐渐降低，而铁磁性则是先增强后减弱.与磁特性相对应，样品的电阻率随着Cu掺杂浓度的增加表现出先减小后增大的特征，并且在整个测量温区内始终呈现绝缘体型导电行为——从顺磁绝 关键词： 1-xCu_xO₃')" href="#">LaMn_1-xCu_xO₃ 导电行为 磁特性     

Possible quantum critical point in La(2/3)Ca(1/3)Mn(1-x)Ga x O3

We study the magnetic ground state in La(2/3)Ca(1/3)Mn(1-x)Ga x O3 manganites, where a quantum critical point (QCP) has been theoretically predicted. The metallic ferromagnetic ground state for low Ga doping breaks down for x > or = 0.11, an insulating state being established at low temperatures. Long-range ferromagnetism coexists with short-range magnetic correlations in the concentration range 0.11 < or = x < or = 0.145 while only the short-range correlations survive for x > or = 0.16. We discuss the implications of such a QCP to the physics of manganites and compare to other QCP systems.     

透明导电半导体ZnO膜的研究

本文采用独特的电子束蒸镀方法，在光学镀膜机上，以 ＺｎＯ＋３％Ａｌ２Ｏ３和 ＺｎＯ为膜料．ｋ９光学玻璃为衬底，制备出ＺｎＯ 膜。膜层为多晶膜，可见光透过率为Ｔ＝７０－９０％，电阻率ｐ＝１×１０－５Ω·ｍ，方电阻为 Ｒ　＝１５０±５０±５０Ω／　，膜机械强度超过国标单层标准，找到实用最佳工艺条件。     

Influence of Ni/Mn ratio on magnetostructural transformation and magnetocaloric effect in Ni_(48-x)Co_2Mn_(38+x)Sn_(12)(x = 0, 1.0, 1.5, 2.0,and 2.5) ferromagnetic shape memory alloys

An investigation on the magnetostructural transformation and magnetocaloric properties of Ni_(48-x)Co_2Mn_(38+x)Sn_(12)(x = 0, 1.0, 1.5, 2.0, and 2.5) ferromagnetic shape memory alloys is carried out. With the partial replacement of Ni by Mn in the Ni_(48)Co_2Mn_(38)Sn_(12) alloy, the electron concentration decreases. As a result, the martensitic transformation temperature is decreased into the temperature window between the Curie-temperatures of austenite and martensite. Thus, the samples with x = 1.5 and 2.0 exhibit the magnetostructural transformation between the weak-magnetization martensite and ferromagnetic austenite at room temperature. The structural transformation can be induced not only by the temperature,but also by the magnetic field. Accompanied by the magnetic-field-induced magnetostructural transformation, a considerable magnetocaloric effect is observed. With the increase of x, the maximum entropy change decreases, but the effective magnetic cooling capacity increases.     

Magnetization depth profile of (Fe/Dy) multilayers

An experimental and numerical study of the magnetization in (Fe 3 nm/Dy 2 nm) multilayers is presented. The samples were thermally evaporated under ultra-high vacuum at two different substrate temperatures, 320 and 570 K. In order to get the magnetization depth profile of these transition metal/rare earth (TM/RE) multilayers, a fine investigation of the structural, chemical, and magnetic properties was carried out. The samples were studied by X-ray reflectivity (XRR), high resolution transmission electron microscopy (HRTEM), conversion electron Mössbauer spectrometry (CEMS), SQUID magnetometry and polarized neutron reflectivity (PNR). Magnetization profiles were obtained by Monte Carlo simulations to support the PNR fits. The key role of the crystalline structure is emphasized by magnetic depth profile measurements performed using polarized neutron reflectometry. The antiparallel configuration of Fe and Dy layers’ magnetizations was evidenced, as well as the perpendicular magnetic anisotropy (PMA), especially in the case of the sample prepared at 570 K.     

Characterizations of n-type ferromagnetic GaMnN thin film grown on GaN/Al2O3 (0 0 0 1) by metal-organic chemical vapor deposition

A high-quality ferromagnetic GaMnN (Mn=2.8 at%) film was deposited onto a GaN buffer/Al₂O₃(0 0 0 1) at 885 °C using the metal-organic chemical vapor deposition (MOCVD) process. The GaMnN film shows a highly c-axis-oriented hexagonal wurtzite structure, implying that Mn doping into GaN does not influence the crystallinity of the film. No Mn-related secondary phases were found in the GaMnN film by means of a high-flux X-ray diffraction analysis. The composition profiles of Ga, Mn, and N maintain nearly constant levels in depth profiles of the GaMnN film. The binding energy peak of the Mn 2p_3/2 orbital was observed at 642.3 eV corresponding to the Mn (III) oxidation state of MnN. The presence of metallic Mn clusters (binding energy: 640.9 eV) in the GaMnN film was excluded. A broad yellow emission around 2.2 eV as well as a relatively weak near-band-edge emission at 3.39 eV was observed in a Mn-doped GaN film, while the undoped GaN film only shows a near-band-edge emission at 3.37 eV. The Mn-doped GaN film showed n-type semiconducting characteristics; the electron carrier concentration was 1.2×10²¹/cm³ and the resistivity was 3.9×10⁻³ Ω cm. Ferromagnetic hysteresis loops were observed at 300 K with a magnetic field parallel and perpendicular to the ab plane. The zero-field-cooled and field-cooled curves at temperatures ranging from 10 to 350 K strongly indicate that the GaMnN film is ferromagnetic at least up to 350 K. A coercive field of 250 Oe and effective magnetic moment of 0.0003 μ_B/Mn were obtained. The n-type semiconducting behavior plays a role in inducing ferromagnetism in the GaMnN film, and the observed ferromagnetism is appropriately explained by a double exchange mechanism.     

室温下Ga1-xHoxN (x=0.0 and 0.05)稀磁半导体薄膜磁性

采用热蒸镀技术和后续氨退火制备了Ho掺杂GaN稀磁半导体薄膜. X射线衍射分析表明,所有的峰属于六角纤锌矿结构. 利用扫描电子显微镜和能量色散谱分别进行了表面形貌和成分分析. 用振动样品磁强计在室温测定了Ga_1-xHo_xN(x=0.0,0.05)的室温铁磁性. 磁性测量结果表明,未掺杂薄膜GaN具有抗磁性行为,而Ho掺杂Ga_0.95Ho_0.05N的薄膜表现出铁磁行为.     

LARGE MAGNETIC ENTROPY CHANGE NEAR CHARGE-ORDERED TRANSITION TEMPERATURE IN PEROVSKITE-TYPE MANGANITE

The magnetocaloric effect in polycrystalline of Pr_1-xSr_xMnO₃ (x=0.33, 0.43, 0.50) has been investigated. A large magnetic entropy change (7.1J/kgK) was discovered in Pr_0.5Sr_0.5MnO₃ under a low magnetic field of 1T at charge-ordered state transition temperature (161K). The physical mechanism is related to a drastic magnetization change at a temperature where the field-induced magnetic, electron and structural phase transitions occur (from the antiferromagnetic charge-ordered state to the ferromagnetic charge-disordered state).     

Reentrant spin glass behavior in Cr-doped perovskite manganite

The magnetic and transport properties of the Cr-doped manganites La(0.46)Sr(0.54)Mn(1-y)Cr(y)O3 ( 0 < or = y < or = 0.08) with the A-type antiferromagnetic structure were investigated. Upon cooling, we find multiple magnetic phase transitions, i.e., paramagnetic, ferromagnetic (FM), antiferromagnetic (AFM), and spin glass in the y = 0.02 sample. The low temperature spin glass state is not a conventional spin glass with randomly oriented magnetic moments but has a reentrant character. The reentrant spin glass behavior accompanied by the anomalous multiple magnetic transitions might be due to the competing interactions between the FM phase and the A-type AFM matrix induced by the random Cr impurity.     

Relaxation of the magnetic state of a ferromagnetic–superconducting layered structure

We have proposed a real-time method of neutron reflectometry. The magnetic state of the Ta/V/FM/Nb/Si ferromagnetic–superconducting system has been analyzed. Relaxation of the inhomogeneous magnetic state with a characteristic time of several hours, which depends on the magnetic field magnitude and temperature, has been observed. The relaxation of the domain structure has changed upon a transition of the V and Nb layers to the superconducting state. It has been concluded that real-time reflectometry data for polarized neutrons are important for determining the origin of magnetism in ferromagnetic–superconducting layered structures.     

Exotic d-wave superconducting state of strongly hole-doped K(x)Ba(1-x)Fe2As2

We investigate the superconducting phase in the K(x)Ba(1-x)Fe2As2 122 compounds from moderate to strong hole-doping regimes. Using the functional renormalization group, we show that, while the system develops a nodeless anisotropic s(±) order parameter in the moderately doped regime, gapping out the electron pockets at strong hole doping drives the system into a nodal (cos k(x) + cos k(y))(cos k(x) - cos k(y)) d-wave superconducting state. This is in accordance with recent experimental evidence from measurements on KFe2As2 which observe a nodal order parameter in the extreme doping regime. The magnetic instability is strongly suppressed.