Spin-engineering in the Co75Fe25/Cu(1 1 0) system

We present results on the growth and magnetic anisotropies of Co₇₅Fe₂₅ films grown on a Cu(1 1 0) single crystal. Angular dependent MOKE measurements show a thickness dependent, in-plane rotation of the easy axis of magnetisation of up to 60° from the [0 0 1] direction (towards [−1 1 0]). For a film thickness of 5 ML, just greater than that required for the onset of ferromagnetism, uniaxial anisotropy is observed with the easy axis along the [0 0 1] direction. As the film thickness increases this is seen to rotate in-plane towards the [−1 1 0] direction as the contribution from the cubic anisotropy constant grows. At a film thickness of 9 ML there is predominantly cubic anisotropy and at 10 ML the easy axis is rotated to 150° with respect to the [1 −1 0] axis, where it is stabilised.     

The crystallographic texture and magnetic anisotropy of melt-spun CeCo5.4 ribbon

CeCo_5.4 ribbons have been prepared by melt spinning at wheel speeds v=5, 15, 25 and 35 m/s. The ribbons are essentially single 1:5 phase, and have significant crystallographic texture and magnetic anisotropy. The ribbon's longitudinal direction is easy direction, and normal to the ribbon plane direction is hard direction. For v=5 m/s [1 1 1]-axes of the grains near non-contact surface of the ribbon are normal to the ribbon plane. With increase of v, [1 1 0] and [2 0 0]-axes of the grains near non-contact surface rotate toward the normal direction and the c-axes parallel to the ribbon plane. The anisotropy increases up to v=25 m/s and then decreases. The grains near contact-wheel surface are randomly oriented for all v. The coercivity increases with increase of v due to decrease of the grain size. The values of coercivity are smaller in the easy direction and are larger in the hard direction, meaning that the coercivity mechanism is mainly characterized by domain wall pinning.     

Magnetic anisotropy and spin-reorientation in HoAl2

Torque measurements have been performed at several temperatures and magnetic fields, on a single crystal of HoAl₂ in the (1 1 0) plane. The easy magnetization direction changes from the [1 0 0] to [1 1 0] near T_R = 20 K in magnetic fields between 0.2 and 1.6 T. At temperatures below T_R a new non-major cubic symmetry easy direction appears which rotates with temperature in the plane of the sample. This behaviour and that of the complete torque curves have been interpreted on the basis of a single ion model.     

Magnetization and torque measurements on Nd2Fe14B single crystals

Magnetization and torque measurements on single crystal specimens of Nd₂Fe₁₄B have been carried out. The magnetization values measured always in the direction of easy magnetization and those in the [001] direction have been precisely determined at temperatures from 4.2K to 600K with a superconducting magnet up to 52.65 kOe. Below the spin reorientation temperature 135K, the magnetization value of the direction of easy magnetization increases anomalously with decreasing temperature. The direction of easy magnetization tilts from the [001] axis to the [110] axis and this tilt angle has been also precisely determined by torque measurement in the temperature range below the spin reorientation temperature. The four-fold symmetry in torque curve for the (001) plane is continously observed at even up to near room temperature and the [110] direction of easy magnetization and the [100] direction of hard magnetization do not change below and above the spin reorientation temperature.     

Easy axis reorientation and magneto-crystalline anisotropic resistance of tensile strained (Ga,Mn)As films

We present a study of magnetic anisotropy by using magneto-transport and direct magnetization measurements on tensile strained (Ga,Mn)As films. The magnetic easy axis of the films is in-plane at low temperatures, while the easy axis flips to out-of-plane when temperature is raised or hole concentration is increased. This easy axis reorientation is explained qualitatively in a simple physical picture by Zener’s p-d model. In addition, the magneto-crystalline anisotropic resistance was also investigated experimentally and theoretically based on the single magnetic domain model. The dependence of sheet resistance on the angle between the magnetic field and [1 0 0] direction was measured. It is found that the magnetization vector M in the single-domain state deviates from the external magnetic field H direction at low magnetic field, while for high magnetic field, M continuously moves following the field direction, which leads to different resistivity function behaviors.     

The magnetic properties and anisotropy of the linear chain compound TlFe3Te3

The magnetic properties of TlFe₃Te₃ are studied on powdered samples and single crystals. Below 220 K TlFe₃Te₃, is a very anisotropic ferromagnet, the crystallographic c axis being the easy axis of magnetization. While in the easy direction saturation is achieved below 0.5 kOe, in the hard direction saturation is reached at 64 kOe. The angular dependence of the magnetization follows closely a cos ¦?¦ law. The magnetic transition is very abrupt at low external fields, suggesting a first order phase transition. It is accompanied by a small anomaly in the thermal dilatation of the c axis. The magnetization shows an anomalous increase below 50 K suggesting a phase transition.     

CoPt alloy grown on the WSe2(0 0 0 1) van der Waals surface

The structural and magnetic properties of 3-nm-thick CoPt alloys grown on WSe₂(0 0 0 1) at various temperature are investigated. Deposition at room temperature leads to the formation of a chemically disordered fcc CoPt alloy with [1 1 1] orientation. Growth at elevated temperatures induces L1₀ chemical order starting at 470 K accompanied with an increase in grain size and a change in grain morphology. As a consequence of the [1 1 1] growth direction, the CoPt grains can adopt one of the three possible variants of the L1₀ phase with tetragonal c-axis tilted from the normal to the film plane direction at 54°. The average long-range order parameter is found to be 0.35(±0.05) and does not change with the increase in the deposition temperature from 570 to 730 K. This behavior might be related to Se segregation towards the growing facets and surface disorder effects promoted by a high surface-to-volume ratio. Magnetic studies reveal a superparamagnetic behavior for the films grown at 570 and 730 K in agreement with the film morphology and degree of chemical order. The measurements at 10 K reveal the orientation of the easy axis of the magnetization lying basically in the film plane.     

Ni51Zr49非晶合金晶化过程的电子显微镜研究

用透射电子显微镜对Ni₅₁Zr₄₉非晶合金的晶化过程进行了研究,发现晶化初期首先从非晶基体上析出的是具有C心单斜点阵的NiZr＇相,a=0.3268nm,b=0.4101nm,c=0.5224nm,β=71.8°。与稳定相NiZr有很明确的取向关系:[100]_NiZr＇∥[100]_NiZr [001]_NiZr＇∥[110]_NiZr。它可以看成是NiZr相的亚稳态或超结构。随温度升高,逐渐转变成NiZr相。温度再高时,在非晶基体上还会析出少量Ni₁₀Zr₇相。晶化初期,无论是NiZr还是NiZr＇相,都是以多次孪晶的形式析出。孪晶有这两种基本形式,一种是以NiZr或NiZr＇的[021]方向为轴的180°孪晶,一种是以NiZr的[001]或NiZr＇的[010]方向为轴的36°旋转孪晶,其它孪晶为这两种孪晶方式的重复与组合。随着温度的升高,孪晶逐渐减少。 关键词：     

Magnetostriction of antiferromagnetic FeGe2

The anisotropic magnetostriction of FeGe₂ is measured for magnetic field along the [1 0 0] and [1 1 0] axes at temperature 4.2 K and along [1 0 0] from 77 to 300 K. The behaviour is consistent with spin reorientation in the basal plane. The saturation magnetostriction and the characteristic field required to produce saturation decrease with increasing temperature and approach zero at the lower transition temperature, $\text{T}{}_{\mathrm{K}}\text{? 265}$ K. This suggests that the spins flip from the basal plane into the direction of the tetragonal [0 0 1] axis at T_K.     

Metamagnetic states in single crystal HoNi<Subscript>2</Subscript>B<Subscript>2</Subscript>C at <Emphasis Type="Italic">T</Emphasis> ≈ 1.9 K: Torque magnetometry study

Metamagnetic transitions in single-crystal rare-earth nickel borocarbide HoNi₂B₂C have been studied at T ≈ 1.9 K with a Quantum Design torque magnetometer. With increasing field, transitions to antiferromagnetic, ferrimagnetic, non-collinear, and saturated paramagnetic states take place. The critical fields of the transitions depend crucially on the angle θ between applied field and the easy axis [110]. Measurements of torque along the c axis have been made while changing the angular direction of the magnetic field (parallel to basal tetragonal ab planes) and with changing field at fixed angle over a wide angular range. Two new phase boundaries in the region of the non-collinear phase have been observed, and the direction of the magnetization in this phase has been precisely determined. At low field the antiferromagnetic phase is observed to be multidomain. In the angular range around the hard axis (?6° ≤ ? ≤ 6°, where ? is the angle between the field and hard axis [100]) the magnetic behavior is found to be “frustrated” with a mixture of phases with different directions of the magnetization.     

Magnetic properties of A DyNi2 single crystal

Magnetic measurements have been performed on a single crystal of DyNi₂ in applied fields up to 135 kOe. In the ferromagnetic range (T_c = 25 K), the easy magnetization direction is [100] and the hardest one is [111]. Crystal field parameters have been determined from the field and temperature dependence of the magnetization measured along the three principal axes. A two-dimensional model has been used to take into account the rotation of magnetization towards the field. The deduced parameters are W = -0.8 K and x = 0.49. The corresponding anisotropy is very large: especially even a field of 135 kOe applied along a difficult magnetization axis cannot rotate the magnetization along this direction.     

Magnetization reorientation in HoCo2

In order to confirm the magnetization reorientation in HoCo₂, torque measurements have been performed at various temperatures on a spherical single crystal, in the (001) and (011) planes. The easy magnetization direction is the [110] axis at 4.2 K and the [100] axis above 16 K. Furthermore, between 11 K and 16 K, the easy magnetization direction rotates progressively within the (001) plane. These results agree with the magnetization measurements and can be interpreted by a crystal field model.     

Parelektrische Resonanz von Li+ in KCl

Parelectric resonance (PER) absorption spectra of Li⁺-centers in KCl crystals are measured at 35 and 9 GHz. Measurements for the microwave fieldE ₁ parallel and perpendicular to the static fieldE ₀ for three different orientations relative to the crystal axes can be explained by using the following offcenter tunneling model for the Li⁺-center: The dipole momentp=6.3±0.3 Debye is in [111] direction. Tunneling transitions are possible parallel to the [100] and [110] axis. The corresponding matrix elements are 11.3±0.5 and 3.2±0.5 GHz. The zero field splittings are 9.8±1.5; 22.6±1 and 35.4±3 GHz. Measurements under application of an uniaxial pressureP ₀ support this analysis.     

Raman active modes of NiSi crystal

Raman scattering intensities of the NiSi Raman-active modes have been calculated with three Raman measurement configurations, which can be used for the symmetry assignment of the NiSi Raman peaks. Raman-active vibrations of the NiSi crystal have also been theoretically studied. Results show that the lattices with A_g and B_2g modes vibrate only in the plane normal to the NiSi[0 1 0] direction while the lattices with B_1g and B_3g modes vibrate only along the NiSi[0 1 0] axis. Based on such study, the relationship between the anisotropic strain distribution in the NiSi thin film and the Raman peak shifts has been briefly discussed.     

Structural and magnetic properties of thin epitaxial Fe films on (1 1 0) GaAs prepared by metalorganic chemical vapor deposition

Iron films have been grown on (1 1 0) GaAs substrates by atmospheric pressure metalorganic chemical vapor deposition at substrate temperatures (T_s) between 135°C and 400°C. X-ray diffraction (XRD) analysis showed that the Fe films grown at T_s between 200°C and 330°C were single crystals. Amorphous films were observed at T_s below 200°C and it was not possible to deposit films at T_s above 330°C. The full-width at half-maximum of the rocking curves showed that crystalline qualities were improved at T_s above 270°C. Single crystalline Fe films grown at different substrate temperature showed different structural behaviors in XRD measurements. Iron films grown at T_s between 200°C and 300°C showed bulk α-Fe like behavior regardless of film thickness (100–6400 Å). Meanwhile, Fe films grown at 330°C (144 and 300 Å) showed a biaxially compressed strain between substrate and epilayer, resulting in an expanded inter-planar spacing along the growth direction. Magnetization measurements showed that Fe films (>200 Å) grown at 280°C and 330°C were ferromagnetic with the in-plane easy axis along the [1 1 0] direction. For the thinner Fe films (⩽200 Å) regardless of growth temperature, square loops along the [1 0 0] easy axis were very weak and broad.     

[Co/Pd]4–Co–Pd–NiFe spring magnets with highly tunable and uniform magnetization tilt angles

By varying the Pd thickness (t_Pd) from 0 to 8 nm in [Co/Pd]₄/Co/Pd(t_Pd)/NiFe exchange springs, we demonstrate (i) continuous tailoring of the exchange coupling between a [Co/Pd]₄/Co layer with perpendicular anisotropy, and a NiFe layer with an in-plane easy axis, (ii) tuning of the NiFe out-of-plane magnetization angle from 20^○ to 80^○, and (iii) an up to two-fold increase in the NiFe damping. The partial decoupling also results in a highly uniform NiFe magnetization. These properties make [Co/Pd]₄/Co/Pd(t_Pd)/NiFe spring magnets ideal candidates for use as tilted polarizers, by combining stable and well-defined spin directions of its carriers with a high degree of angular freedom.     

Magnetoelastic effects in terbium

The variation of the elastic modulus C₃₃ of terbium has been investigated as a function of temperature in the range 200–230 K, which includes the whole of the antiferromagnetic phase, and as a function of magnetic field applied along the easy magnetic direction, the b axis. Hysteresis in C₃₃ in the antiferromagnetic phase is interpreted in terms of spiral spin domains. The magnetic phase changes are reflected in anomalies in the elastic constant and these are used to produce a magnetic phase diagram of terbium. The final phase diagram has been compared with earlier measurements of magnetisation and magnetostriction.     

Growth of Al2O3 thin films on NiAl(1 0 0) by gas-phase oxidation and electro-oxidation

The growth and structures of aluminum oxides on NiAl(1 0 0) have been investigated by RHEED (reflection high energy electron diffraction), complemented by LEED (low energy electron diffraction), AES (Auger electron spectroscopy) and STM (scanning tunneling microscopy). Crystalline θ-Al₂O₃ phase grows through gas-phase oxidation on the NiAl(1 0 0) substrate with its a and b-axes parallel to [0 −1 0] and [0 0 1] direction of the substrate, respectively, forming a (2 × 1) unit cell. Whilst, three-dimensional nano-sized NiAl(1 0 0) protrusions and Al₂O₃, NiAl(0 1 1) clusters were found to co-exit at the surface, evidenced by extraordinary transmission spots superposed to the substrate reflection rods in the RHEED patterns. Particularly, the NiAl(0 1 1) clusters develop with their (0 1 1) plane parallel to the NiAl(1 0 0) surface, and [1 0 0] axis parallel to the [0 −1 1] direction of the substrate surface. STM observation combined with information from AES and TPD (temperature programmed desorption) suggest the formation of these 3D structures is closely associated with partial decomposition of the crystalline oxides during annealing. On the other hand, smoother (2 × 1) oxide islands with thickness close to a complete monolayer of θ-Al₂O₃ can be formed on NiAl(1 0 0) by electro-oxidation, in contrast with the large crystalline films formed by gas-oxidation.     

Temperature dependence of coercivity and metamagnetism in Tb0.5Y0.5Ni

The temperature dependences of magnetic properties of the FeB structure compound Tb_0.5Y_0.5Ni are examined with the aim to elucidate the origin of intrinsic magnetic hardness in this compound. The easy a axis coercivity of an aligned powder sample is found to be strongly temperature dependent. A domain wall activation model is employed to obtain the parameters H₀(0)=30kOe, V_V(0)=0.24K^?1, and β=0.016K^?1, where H₀(0) is the coercive force at absolute zero, V_T(0) the domain wall activation parameter, and β the coefficient for the linear temperature dependence of the reduced anisotropy. From polycrystalline data, we find a strong temperature dependence of the c axis metamagnetic transition only for the ferromagnetic (F) to antiferromagnetic (AF) direction. From the relative constancy of the AF to F c axis metamagnetic transition compound to the a axis coercivity we conclude that the coercive force is not directly related to the local molecular fields as had been previously suggested.     

Magnetic structures of the rare earth orthotitanites RTiO3; R = Tb,Dy, Tm and Yb

The magnetic structures of the rare earth orthotitanites, RTiO₃, R = Tb, Dy, Tm and Yb, have been solved using neutron powder diffraction techniques.Two different types of magnetic structure have been found. One has the titanium and rare earth moments antiparallel along the c axis. The other structure has the rare earth moments in the ab plane with both ferromagnetic and antiferromagnetic components. In TbTiO₃, the terbium moment of (8.1 ± 0.4)μ_β has ferromagnetic and antiferromagnetic components along the [100] and [010] directions, respectively, with the moments lying at an angle of (36 ± 3)° to the [100] direction. In DyTiO₃, the dysprosium moment of (9.7 ± 0.7)μ_β has ferromagnetic and antiferromagnetic components along the [010] and [100] directions, respectively, with the moments making an angle of (31 ± 5)° to the [010] direction. TmTiO₃ has a thulium moment of (6.0 ± 0.4)μ_β in a ferromagnetic array along the [001] direction. The average titanium moment in the orthotitanites is (0.7 ± 0.3)μ_β in a direction antiparallel to the ferromagnetic component of the rare earth moment. The ytterbium moment in YbTiO₃ is quenched. It is found to be (1.7 ± 0.2)μ_β assuming a moment direction along [001]. The rare earth moment directions are found to be remarkably consistent in the series RMO₃, M = Ti, Cr, Fe and Al.