On the formation of a phase with tenfold symmetry in amorphous Ni–Zr alloys

The magnetic anisotropy energy (MAE) of 3d transition-metal wires, stripes, and films is calculated self-consistently as a function of stripe width and film thickness. The magnetization-reorientation transitions in stripes are determined along the crossover from the mono-atomic one-dimensional chain to the two-dimensional monolayer. It is shown that the MAE oscillates as a function of stripe width and depends strongly on the considered transition metal. The reorientation transitions in Co films deposited on a highly polarizable substrate such as Pd are discussed. A local analysis of the layer-resolved MAEs provides new insights into the off-plane magnetization observed in Pd-capped Co films on Pd(111). The interfaces responsible for the stability of the off-plane easy axis are characterized microscopically. An unexpected internal magnetic structure of the Co–Pd interfaces is revealed in which the magnetic moments and spin–orbit interactions at Pd atoms play a crucial role. The nature of the reorientation transition from perpendicular to in-plane magnetization with increasing film thickness is studied by means of full-vectorial calculations. The existence of a spin-canted phase at intermediate film thickness is demonstrated.     

The description of the domain structure in thin ferromagnetic films with thickness near the critical value

The magnetization distribution is considered in a thin ferromagnetic film of a thickness near the critical value, for which the continuous phase transition from the homogeneous magnetization state to the domain structure appears. The easy axis of the magnetization is perpendicular to the film plane and the anisotropy constant β < 4π. On the basis of the self-consistent theory the vortex-like magnetization distribution in the interdomain wall was obtained. The value of the critical thickness, the period of the domain structure and the amplitudes of the magnetization vector components as dependent on the film parameters were derived.     

Asymmetrically shaped hysteresis loop in exchange-biased FeNi/FeMn film

The magnetization reversal of the bilayer polycrystalline FeNi(50 Å)/FeMn(50 Å) film sputtered in a magnetic field has been studied by magnetic and magneto-optical techniques. The external magnetic fields were applied along the easy or hard magnetization axis of the ferromagnetic permalloy layer. The asymmetry of hysteresis loop has been found. Appreciable asymmetry and the exchange bias were observed only in the field applied along the easy axis. The specific features of magnetization reversal were explained within the phenomenological model that involves high-order exchange anisotropy and misalignment of the easy axes of the antiferromagnetic and ferromagnetic layers. It has been shown that the film can exist in one of three equilibrium magnetic states in the field applied along the easy axis. The transitions between these states occur as first-order phase transitions. The observed hysteresis loop asymmetry is related to the existence of the metastable state.     

Study of Phase Transition Properties in Epitaxial Ferroelectric Film

Based on the transverse Ising model and using decoupling approximation to the Fermi-type Green's function, we study the phase transition properties of the epitaxial ferroelectric film with one substrate. A general recursive equation of the ferroelectric thin film with two n-layer materials is obtained, which enables us to study the phase transition properties for any number layers forepitaxial ferroelectric thin film. With the help of this equation, we analyze the effect of the exchange interaction and the transverse field in the phase diagram, the influence to the polarizations and Curie temperature numerically. The results show that epitaxial ferroelectric film are able to induce a strong increase or decrease of Curie temperature to different exchange interactions and transverse fields within the epitaxial film layers. The theoreticalresults are in reasonable accordance with experimental data of different ferroelectric thin film.     

Transitional periodic domain structure in thin films of magnetically uniaxial materials

The paper gives the theory of transitional domain structure in thin films of uniaxial ferromagnets with easy axis perpendicular to the film. It is proved that in a certain range of thicknesses this structure is energetically more advantageous than the plate structure originally proposed by Kittel. The proposed model explains the transition from the Kittel structure to the homogeneously magnetized film.The authors thank Z. Málek C. Sc. and V. Janovec C. Sc. for valuable remarks and V. Kamberský for help in the numerical calculations.     

Tunable in-plane spin orientation in Fe/Si(557) film by step-induced competing magnetic anisotropies

Although the spin-reorientation transition from out-of-plane to in-plane in Fe/Si film is widely reported, the tuning of in-plane spin orientation is not yet well developed. Here, we report the thickness-, temperature- and Cu-adsorptioninduced in-plane spin-reorientation transition processes in Fe/Si(557) film, which can be attributed to the coexistence of two competing step-induced uniaxial magnetic anisotropies, i.e., surface magnetic anisotropy with magnetization easy axis perpendicular to the step and volume magnetic anisotropy with magnetization easy axis parallel to the step. For Fe film thickness smaller than 32 monolayer(ML), the magnitudes of two effects under various temperatures are extracted from the thickness dependence of uniaxial magnetic anisotropy. For Fe film thickness larger than 32 ML, the deviation of experimental results from fitting results is understood by the strain-relief-induced reduction of volume magnetic anisotropy.Additionally, the surface and volume magnetic anisotropies are both greatly reduced after covering Cu capping layer on Fe/Si(557) film while no significant influence of Na Cl capping layer on step-induced magnetic anisotropies is observed.The experimental results reported here provide various practical methods for manipulating in-plane spin orientation of Fe/Si films and improve the understanding of step-induced magnetic anisotropies.     

微细矩形磁性薄膜体系中一致转动磁化模式

针对经过刻蚀的微细矩形磁性体系，将样品的形状及其磁晶易磁化轴的偏转两个因素引入经典的Stoner-Wohlfarth一致转动磁化模型中，发现磁性样品的微细化将使其特征星形线发生膨胀，而样品形状的缺陷及磁晶易磁化轴的偏转都将导致样品非对称特征星形线的产生.这些结果说明在诸如磁性随机存储器等基于微细磁性薄膜的工作中，薄膜形状及其磁晶易磁轴的角度不容忽略. 关键词： 磁性薄膜 Stoner-Wohlfarth模型 特征星形线 各向异性     

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.     

Magnetostriction of a single cubic laves phase compound Tb0.27Dy0.73Fe2

The magnetostriction of a single crystal cubic Laves phase compound Tb_0.27Dy_0.73Fe₂ is measured with the applied field (0–25 kOe) in the [111] direction in the temperature range between 80 and 300 K. Evidence is seen of a possible transition to the[uv0] easy axis phase during the spin re-orientation form [100] easy axis direction to the [110] easy axis direction.     

Azimuthal anchoring energy at the interface between a nematic liquid crystal and a PTFE substrate

The azimuthal anchoring energy of the nematic liquid crystal 4-pentyl-4'-cyanobiphenil (5CB) on a poly(tetrafluoroethylene) (teflon, PTFE) film is measured for the first time. The PTFE film is deposed using the Wittmann and Smith technique which consists on rubbing a bar of this polymer against a glass substrate at a controlled temperature and pressure. Measurements of the azimuthal anchoring energy are made with a reflectometric technique which provides high accuracy and sensitivity. The dependence of the azimuthal anchoring energy on temperature and on the rubbing pressure is investigated. The extrapolation length remains virtually constant in the whole temperature range of the nematic phase except for an increase of 25% close to the clearing temperature. The azimuthal anchoring energy is somewhat strong and increases with increasing the deposition pressure of PTFE. The observation of a relevant pre-transitional anisotropy of the reflection coefficients in the isotropic phase proves that the surface interactions favor an excess of orientational order. Ageing of the anchoring energy and gliding of the easy axis are experimentally observed. Both these phenomena suggest the presence of an anisotropic adsorbed layer of nematic molecules on the PTFE film.     

Influence of Surface Transition Layers on Phase Transformation and Pyroelectric Properties of Ferroelectric Thin Film

Taking into account surface transition layers （STLs）, we study the phase transformation and pyroelectric properties of ferroelectric thin films by employing the transverse Ising model （TIM） in the framework of the mean field approximation. The distribution functions representing the intra-layer and inter-layer couplings between the two nearest neighbour pseudo-spins are introduced to characterize STLs. Compared with the results obtained by the traditional treatments for the thin films using only the single surface transition layer （SSL）, it is shown that the STL model reflects a more realistic and comprehensive situation of films. The effects of various parameters on the phase transformation properties have shown that STL can make the Curie temperature of the film higher or lower than that of the corresponding Sulk material, and the thickness of STL is a key factor influencing the film properties. For a film with definite thickness, there exists a critical STL thickness at which ferroelectricity will disappear when the intra-layer and inter-layer interactions are weak.     

Magnetic anisotropy of transition-metal interfaces from a local perspective: reorientation transitions and spin-canted phases in Pd capped Co films on Pd(111)

Layer-resolved self-consistent electronic calculations of magnetic anisotropy energy (MAE) provide new insight to the off-plane magnetization observed in Pd capped Co films on Pd(111). We demonstrate that the transition from perpendicular to in-plane phases with increasing film thickness involves an intermediate spin-canted phase. The interfaces responsible for the stability of the off-plane easy axes are characterized microscopically. A local analysis of the MAEs reveals an unexpected internal magnetic structure of the Co-Pd interfaces in which the magnetic moments and spin-orbit interactions at the Pd atoms play a crucial role.     

Mn和Co线性单原子链填充Cu纳米管的稳定性和磁性

基于密度泛函理论框架下的第一性原理计算,系统地研究了过渡金属(TM)Mn和Co线性单原子链填充Cu纳米管所形成复合结构的稳定性和磁性.相对于孤立单原子链,复合结构的结合能大大增加,表明Cu纳米管的包裹使得Mn和Co单原子链的稳定性显著增强.随着管内TM原子间距的增加,Mn@CuNT复合结构表现出由反铁磁向铁磁的磁相变,而Co@CuNT复合结构则表现出由铁磁向反铁磁的磁相变.相对于自由单原子链,复合结构的磁晶各向异性能显著增强,且Cu纳米管的包裹使得Mn原子链的易磁化方向发生了改变.     

Low temperature magnetism in the rare-earth perovskite GdScO_3

The magnetic phase diagram of rare-earth perovskite compound, GdScO_3, has been investigated by magnetization and heat capacity. The system undergoes an antiferromagnetic phase transition at T_N= 2.6K, with an easy axis of magnetization along the a axis. The magnetization measurements show that it exists a spin-flop transition around 0.3 T for the applied field along the a axis. The critical magnetic field for the antiferromagnetic-to-paramagnetic transition is near 3.2 T when temperature approaches zero. By scaling susceptibilities, we presume this point(B = 3.2 T, T = 0 K) might be a fieldinduced quantum critical point and the magnetic critical fluctuations can even be felt above TN.     

Measurement of the temperature variation of the easy direction of Gd using phase theory

Results for temperature variation of the easy directions of Gd are reported, derived from measurements of its magnetization at subsaturation fields using domain phase theory. The values agree with torque magnetometer results except at close to the easy cone to easy c axis transition temperature which is found to be (224 ± 1) K.     

Field-induced orbital and magnetic phases in Ca3Ru2O7

Magnetic-field- and temperature-dependent Raman scattering studies of Ca3Ru2O7 reveal dramatic field-dependent properties arising from transitions between various complex orbital and magnetic phases, including a field-induced orbital-ordered to orbital-disordered transition (H(o) // hard axis), and a reentrant orbital-ordered to orbital-disordered to orbital-ordered transition (H(o) // easy axis). We find that the dramatic magnetic-field properties are most prevalent in a "mixed"-magnetic and -orbital phase regime, providing evidence for a strong connection between orbital phase inhomogeneity and "colossal" field effects in the ruthenates.     

Two-stage spin-flop transitions in the S = 1/2 antiferromagnetic spin chain BaCu(2)Si(2)O(7)

Two-stage spin-flop transitions are observed in the quasi-one-dimensional antiferromagnet BaCu(2)Si(2)O(7). A magnetic field applied along the easy axis induces a spin-flop transition at 2.0 T followed by a second transition at 4.9 T. The magnetic susceptibility indicates the presence of Dzyaloshinskii-Moriya (DM) antisymmetric interactions between the intrachain neighboring spins. We discuss a possible mechanism whereby the geometrical competition between DM and interchain interactions, as discussed for the two-dimensional antiferromagnet La(2)CuO(4), causes the two-stage spin-flop transitions.     

Direct experimental investigation of spin-reorientation phase transitions in an antiferromagnetic CoNiCu/Cu superlattice

The characteristic features of phase transitions induced by an external magnetic field and of the corresponding changes in the relative orientations of the spins in the ferromagnetic CoNiCu layers of a multilayer film, which are coupled by an antiferromagnetic exchange interaction via nonmagnetic Cu interlayers, are studied using a magnetooptic method for visualizing the fringing fields. It is established that the magnetization reversal process in this nanocomposite material proceeds by a spin-flop orientational phase transition on account of the formation and motion of specific domain walls as well as by incoherent rotation of the spins toward the applied field. It is shown that, depending on the direction of the external magnetic field with respect to the easy axis, asymmetric canted phases also arise as a result of such transitions. Pis’ma Zh. Tekh. Fiz. 64, No. 11, 778–782 (10 December 1996)     

Critical dielectric relaxation of highly deuterated betaine arsenate at microwave frequencies

The dielectric behavior of highly deuterated betaine arsenate in the frequency range up to 11 GHz is described by a Cole-Davidson relaxation. The characteristic dynamics show a critical slowing down near the para-antiferroelectric phase transition. The temperature dependence of the dielectric constant is analyzed in terms of a pseudo-one-dimensional Ising model. Evidence is given for a dependence of antiferroelectric coupling on deuteration which can explain the change from a ferro- to an antiferroelectric ordering on deuteration. Measurements of the dielectric relaxation under a dc bias field parallel to the critical axis elucidate the unusual phase transition behavior at low temperatures. A multicritical point appears in theE-T-phase diagram. Frustration effects due to competing ferro- and antiferroelectric interactions are not seen.     

Phase transition behaviors of a ferroelectric thin film with long-range interactions

Within the framework of the mean-field approximation, the transverse-field Ising model is used to investigate the surface parameter modification of interaction constants and transverse fields on phase transition behaviors of a ferroelectric thin film with long-range interactions. The variation of Curie temperature as a function of the surface transverse field for different surface interaction constants or thickness is discussed. Meanwhile, the variation of Curie temperature as a function of the surface exchange interaction for different surface transverse fields is examined. In addition, the dependence of Curie temperature on the film thickness for different surface exchange interactions and surface transverse fields is obtained.