Electromagnetic waves in a round rod in the presence of an arbitrarily directed external magnetic field or anisotropy axis

A rigorous theory of the propagation of electromagnetic waves in round anisotropic and semiconductor rods in the presence of an arbitrarily directed anisotropy axis or external magnetic field is developed. New types of independent waves are discovered. Exact dispersion equations are obtained for them, which define the dependence of their spectral characteristics on the parameters of the semiconductor or anisotropic crystal and on the magnitude and direction of the constant external magnetic field. The results of numerical investigations for rods made from a semiconductor or a uniaxial crystal are presented. Zh. Tekh. Fiz. 67, 86–91 (July 1997)     

Magnetocaloric effect, magnetic domain structure and spin-reorientation transitions in HoCo5 single crystals

A study on the magnetocaloric effect (MCE) has been carried out on the HoCo₅ single crystal using a direct method in the temperature range 78-300 K and in a magnetic field of 1.3 T at various orientations of the single crystal with respect to the direction of external magnetic field. Our research has shown that magnetic anisotropy strongly affects magnitude and sign of the MCE in the regions of spin-reorientation phase transitions. In addition, the magnetic domain structure of the HoCo₅ single crystal in (0 0 1) plane in the temperature range from room temperature down to 4.2 K was investigated.     

Scattering of positronic atoms on optical phonons in ionic crystals. Positron thermalization

The time for positron thermalization in ionic crystals due to the interaction of positronic atoms with polarizational optical oscillations of the lattice is calculated. The positronic atom is considered as a dipole with moment p induced by the internal crystal field. The dipole moment is evaluated from the value of the positronic-atom deformation parameter determined from data on the magnetic quenching of positronium. For an NaCl crystal, p 1.91D. The positronium thermalization time in ionic, crystals (for the example of NaCl) is estimated at 10^–1 sec. After this time, not only ortho positronium but also para positronium reached total thermalization.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizida, No. 5, pp. 66–70, May, 1979.     

Magnetic anisotropy and ordering in equiatomic FeCo alloy equilibrium state vs. temperature

A spherical single crystal, initially disordered by quenching, is ordered at different temperatures in the range 400–730°C. The measured magnetic anisotropy energy shows a cubic symmetry characteristic of the degree of order. In the case of a heat treatment carried out under an applied magnetic field, there is an additional uniaxial anisotropy energy which characterises the presence of directional order.     

Anisotropy of the upper critical field and specific heat in V3Si — a superconductor with cubic symmetry

The specific heat of a V₃Si single crystal (T _c=17 K, H _c2=20 T) in magnetic fields up to 8 T isinvestigated experimentally for three orientations of the field relative to the crystallographic directions — H∥〈001〉, H∥〈110〉, and H∥〈111〉. Both the upper critical magnetic field and the specific heat of the mixed state are observed to depend on the orientation of the magnetic field relative to the crystallographic directions (anisotropy): The critical field reaches its maximum value and the specific heat its minimum value in a field along the 〈001〉 direction. The anisotropy scale in both phenomena increases as the magnetic field and reaches 3% in a 6 T field. The interrelationship of the upper critical field anisotropy and the specific-heat anisotropy in type-II superconductors is studied. It is shown that the anisotropy of the specific heat in the mixed state in weak fields can serve as a criterion for nontrivial pairing. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 1, 26–29 (10 January 1999)     

Anisotropy characteristics in a Permalloy film induced by a nonuniform magnetic field

Inhomogeneities were observed for the first time in the magnetic structure of a thin Permalloy film, induced by a strongly nonuniform magnetic field applied in the plane of the substrate during fabrication of the samples. The films were obtained by vacuum deposition using a molecular-beam epitaxy system. A nonuniform field was created on the substrate using four samarium-cobalt magnets. The anisotropy of local sections of the samples was measured using a scanning-ferromagnetic-resonance spectrometer. A strong correlation was observed between the distribution of the magnitude and direction of the local magnetic anisotropy of the film and the magnetic-field distribution in the plane of the substrate. Fiz. Tverd. Tela (St. Petersburg) 40, 1291–1293 (July 1998)     

Anisotropy of the local atomic structure in Fe-(5–6 at. %) Si single crystals as the cause of formation and stability of induced magnetic anisotropy

Fe_{1 ? x} Si_x (x = 0.05–0.06) single crystals were prepared and subjected to various heat treatments for structural studies. X-ray diffuse scattering measurements detected an anisotropy of regions with local B2-type atomic ordering in samples with induced magnetic anisotropy. It was shown that the average size of ordered clusters as measured along an applied dc magnetic field during heat treatment is slightly larger than that in a transverse direction and reaches 10 Å. Such anisotropy of B2-type regions is not observed in magnetically isotropic samples obtained by rapid quenching or by annealing and cooling in a rotating field (or in the absence of an external field). A comparative analysis of the atomic structure, domain structure, and hysteresis loop shape in samples subjected to various treatments demonstrated a correlation between the short-range order and magnetic properties.     

Magnetoelastic nature of the dodecagonal anisotropy in holmium metal

We have investigated the magnetoelastic nature of the dodecagonal anisotropy in the magnetic anisotropy energy (MAE) in the basal plane of the hcp crystalline structure in holmium single crystal. We have proved that the origin of the second harmonic of the hexagonal symmetry in MAE clearly lies on a sixth-order magnetoelastic coupling term. The appearance of a 12-fold anisotropy in MAE in a single crystal having hexagonal symmetry provides a new insight on how the magnetic anisotropy can be modified in a magnetic material with giant spin-lattice coupling.     

Crystal field effects in RERh4B4 compounds (RE = rare earth)

By analysis of a large body of available data, crystal field parameters have been obtained for compounds in the series RERh₄B₄ (RE = rare-earth). These parameters have then been used to calculate properties related to the electronic and magnetic properties of such compounds, and it is shown that a substantial unification of current information is obtained for properties including bulk magnetization (polycrystalline and single crystal), magnetic susceptibility, magnetic anisotropy, Schottky anomalies in the specific heat and suppression of the superconducting transition temperature due to magnetic impurities. In agreement with previous discussions crystal field effects are found to clarify the systematics of magnetic transition temperature, but not to give a full explanation. Other phenomena, such as discrepancies in the magnetic moment of ErRh₄B₄ as measured by neutron diffraction and by Mo¨ssbauer spectroscopy cannot be explained as crystal field related phenomena.     

Anisotropic and large low-field magnetic entropy change in a La4/3Sr5/3Mn2O7 single crystal

We have studied the magnetocaloric effect (MCE) in a bilayered La_4/3Sr_5/3Mn₂O₇ single crystal with applied field along both ab-plane and c-direction. Due to the quasi-two-dimensional structure, the crystal exhibits a strong anisotropy in the MCE. The difference of magnetic entropy change between two crystallographic directions depends on external magnetic fields and has a maximum of 2 J/kg K. A large low-field magnetic entropy change, reaching 3.2 J/kg K for a magnetic field change of 15 kOe, is observed when the applied field is along ab-plane. This large low-field magnetic entropy change is attributed to the rapid change of magnetization in response to external magnetic fields in the easy magnetizing plane.     

Photoinduced changes in the space-modulated magnetic order of a FeBO<Subscript>3</Subscript>:Mg single crystal

An effect of nonpolarized white light on the modulated magnetic structure of a FeBO₃:Mg single crystal, which arises in this light-plane weak ferromagnet in the low temperature range during technical magnetization, has been revealed. It has been found that the degree of the light action on the magnetic state of FeBO₃:Mg depends both on its duration and on the orientation of the spontaneous magnetization vector M of the crystal during illumination. Interpretation of the results obtained has been performed in the context of the “magnetic ripple” theory on the assumption that the absorbed light induces additional uniaxial magnetic anisotropy in the easy plane of the crystal and that the anisotropy axis is collinear to the vector M during illumination.     

On determination of effective mass of the delocalized positronium in NaCl crystals

The angular correlation of the photons of two-quantum annihilation in NaCl crystal was measured at temperatures ranging from 77 to 500 K. The data obtained clearly showed a narrow peak which was earlier observed only at low temperatures. The positronium nature of this peak was examined by applying a magnetic field. The positronium effective mass was found to be (1.5±0.2)2 m₀.     

单晶Ni52Mn24Ga24中马氏体变体择优取向的物理表征

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Double-Q magnetic structures and strong planar anisotropy in tetragonal ErRu2Ge2and ErRu2Si2

Single crystal magnetization measurements and powder neutron diffraction on tetragonal ErRu₂Ge₂ as well as anisotropy of the paramagnetic susceptibility and specific heat measurements on ErRu₂Si₂ are presented. Besides the huge crystal field contribution to the uniaxial anisotropy, which favors the basal plane, a strong in-plane anisotropy is evidenced. From these features and neutron diffraction experiments it is shown that magnetic structures of these materials are double-Q and accordingly non-colinear below their Néel temperature (5.2 and 6.0 K for Ge and Si based compounds, respectively). The magnetic structures induced during the metamagnetic processes are discussed. Received 24 December 1999     

外应力场下铁磁/反铁磁双层膜系统中的交换偏置

采用自由能极小的方法研究了铁磁/反铁磁双层膜系统在外应力场下的交换各向异性.本模型中铁磁层具有单轴磁晶各向异性和立方磁晶各向异性，而反铁磁层仅具有单轴磁晶各向异性，但其厚度趋于半无穷.理论上解析地给出了系统的等效交换偏置和钉扎角(它显示了反铁磁层对铁磁层磁化的钉扎作用)与外应力场之间的关系.数值计算表明：系统的等效交换偏置与外磁场的方向有关，而与其大小无关；然而外应力场的大小和方向均对系统的等效交换偏置有影响，其根源在于外应力场的大小和方向都影响着钉扎角. 关键词： 铁磁/反铁磁双层膜 交换偏置 钉扎角 应力场     

Determination of the in-plane anisotropy field in hexagonal systems via rotational magnetization: Theoretical model and Monte Carlo simulations

The magnetic anisotropy field in thin films with in-plane uniaxial anisotropy can be deduced from the VSM magnetization curves measured in magnetic fields of constant magnitudes. This offers a new possibility of applying rotational magnetization curves to determine the first- and second-order anisotropy constant in these films. In this paper we report a theoretical derivation of rotational magnetization curve in hexagonal crystal system with easy-plane anisotropy based on the principle of the minimum total energy. This model is applied to calculate and analyze the rotational magnetization process for magnetic spherical particles with hexagonal easy-plane anisotropy when rotating the external magnetic field in the basal plane. The theoretical calculations are consistent with Monte Carlo simulation results. It is found that to well reproduce experimental curves, the effect of coercive force on the magnetization reversal process should be fully considered when the intensity of the external field is much weaker than that of the anisotropy field. Our research proves that the rotational magnetization curve from VSM measurement provides an effective access to analyze the in-plane anisotropy constant K ₃ in hexagonal compounds, and the suitable experimental condition to measure K ₃ is met when the ratio of the magnitude of the external field to that of the anisotropy field is around 0.2. Supported by the National Natural Science Foundation of China (Grant Nos. 90505007 and 10774061) Recommended by LI FaShen     

Growth-induced anisotropy in Ba0.6K0.4BiO3 superconducting single crystal

0.6 K_0.4BiO₃ single crystal have been performed to study the nature of the growth-induced anisotropy revealed using chemical etching technique. It was found that this anisotropy is responsible for differences in low-field susceptibility and in hysteresis loops observed for different magnetic field orientations. Received: 9 December 1997/Accepted: 28 May 1998     

NMR signals from 0° domain-wall magnetic inhomogeneities in cubic ferrite-garnet crystals

The Fe⁵⁷ NMR signals from 0° domain-wall magnetic inhomogeneities are studied numerically at sites where a 180° domain wall is stabilized in cubic ferrite-garnet crystals. The dependence of the NMR absorption lineshape on the induced anisotropy constants and on the magnitude of the constant magnetic field is studied. Fiz. Tverd. Tela (St. Petersburg) 41, 269–273 (February 1999)     

Process ν → νγ in strong magnetic field with allowance for posironium contribution to photon dispersion

We have studied the radiative decay of neutrinos with relatively high energies E ? m _e in a strong magnetic field taking into account the effect of a bound electron-positron pair (positronium) on photon dispersion. The allowance for the positronium contribution to the polarization operator of the photon substantially modifies the dispersion relation for the photon and the amplitude of the process in the vicinity of the cyclotron resonance. It is shown that the probability of the ?? ?? ??? process considerably increases when the positronium contribution is taken into account.     

红条毛肤石鳖齿舌牙齿内纳米磁性矿物质的磁各向异性研究

SQUID和磁转矩测量表明红条毛肤石鳖齿舌牙齿内纳米磁性矿物质具有明显的磁各向异性,从能量角度对SQUID和磁转矩曲线的分析发现,这些材料具有明显的单晶单轴特性,对于磁各向异性,起作用的主要是磁晶各向异性。磁化过程中,长条片状纳米磁性矿物质中包含的小纳米晶粒磁畴磁矩转向外磁场方向,直到与外磁场方向一致,达到饱和为止,磁化过程中不存在畴壁的移动。