Magnetocrystalline anisotropy of neutron small-angle scattering from an FeNi invar alloy

Small-angle scattering of neutrons from an Fe₆₅Ni₃₅ single crystal with an applied magnetic field parallel to each of 〈100〉, 〈110〉 or 〈111〉 has shown evidence for magnetocrystalline anisotropy.     

Neutron diffraction study of antiferromagnetic order in UGa3 under pressure

The unique magnetic structure and property of intermetallic uranium compounds UGa₃ have been investigated by neutron diffraction measurements. With applying pressure we succeeded in revealing the magnetic structure of UGa₃. We suppose that the magnetic moment of UGa₃ at low pressures is along the 〈011〉 direction and that at 2.2 GPa along the 〈111〉 direction. The Néel temperature and magnetic moment are reduced with applied pressure.     

Magnetic ordering above room temperature in the sigma-phase of Fe66V34

Magnetic properties of four sigma-phase Fe_100−xV_x samples with 34.4?x?55.1 were investigated by Mössbauer spectroscopy and magnetic measurements in the temperature interval 4.2-300 K. Four magnetic quantities, viz. hyperfine field, Curie temperature, magnetic moment and susceptibility, were determined. The sample containing 34.4 at% V was revealed to exhibit the largest values found up to now for the sigma-phase for average hyperfine field, 〈B〉=12.1 T, average magnetic moment per Fe atom, 〈μ〉=0.89 μ_B, and Curie temperature, T_C=315.3 K. The quantities were shown to be strongly correlated with each other. In particular, T_C is linearly correlated with 〈μ〉 with a slope of 406.5 K/μ_B, as well as 〈B〉 is so correlated with 〈μ〉, yielding 14.3 T/μ_B for the hyperfine coupling constant.     

Acoustic NMR in spin-1 systems

Acoustic magnetic resonance, both pulsed and continuous has been discussed in terms of the Bloch-Wangsness-Redfield formulation of the magnetic resonance phenomenon. The quadrupolar mechanism has been taken for the spin-phonon coupling and the mutual interaction has been treated in the ‘effective field approximation’. The expressions for the power absorbed both for Δm=±1 and Δm=±2 have been obtained. It is found that from the measurements of the relaxation parameters for Δm=±1 and Δm=±2 it is possible to estimate the non-secular contributions to the line-width. The power absorbed in pulse excitation comes out to be small for short pulse (short compared to the relaxation parameter) and it reduces to the value obtained in continuous excitation for a long pulse. It is seen that for a given pulse-width the signal decreases with the increase of the relaxation parameter and this happens as temperature is lowered. The saturation of electromagnetic signal in presence of the acoustic excitation has also been studied. The analysis indicates that the relaxation parameter obtained from the plot of the relative signal (〈〉_ω/〈〉₀) vs the acoustic frequency ω, is always less than its true value which can be determined by observing the frequency dependence of the relative fractional signal defined as [(〈〉₀?〈〉_ω)/〈〉_ω]/[(〈〉₀?〈〉_2ω0)/〈〉_2ω0].     

Spinpolarisation von Feldemissionselektronen aus einkristallinem Wolfram

Field-emitted electrons from tungsten tips extracted in magnetic fields of 3–25 kG at 80 K show spin polarization. The observed polarization is always found to be parallel to the external magnetic field for the polycrystalline and oriented tips (〈100〉, 〈110〉 and 〈111〉) investigated. The maximum values of polarization obtained with these monocrystalline emitters range betweenP _max=11–13 percent.     

Effect of the magnetic field in the plane of a garnet ferrite film with orthorhombic magnetic anisotropy on the dynamics of domain walls

The effect of an in-plane magnetic field on the dependence of the domain-wall velocity on the acting magnetic field is investigated for bismuth-containing garnet ferrite single-crystal films of the composition (Bi,Y,Pr)₃(Fe,Ga)₅O₁₂ with the (210) orientation. The in-plane magnetic field is applied along the 〈120〉 and 〈001〉 crystallographic axes. The domain-wall velocity is measured in directions perpendicular and parallel to the in-plane magnetic field.     

Possibility of utilizing the D-3He fuel cycle with 3He production in a spherical tokamak reactor

Possible operating regimes of a spherical tokamak reactor based on the D-³He fuel cycle with ³He production are considered. The parameters of the plasma and magnetic system are calculated for several versions corresponding to the high power efficiency (with a power gain factor in plasma of Q = 20) in a reactor with an aspect ratio of A = 1.5. According to calculations, for an axial magnetic field in vacuum of B ₀ = 2 T, a plasma radius of a = 3 m, an average 〈β〉 value of 0.53, and a plasma temperature of 〈T〉 = 48 keV, the reactor power can reach P _fus = 500 MW. In order to achieve a power of P _fus = 1500 MW in a reactor with a = 2 m, 〈β〉 = 0.36, and 〈T〉 = 40 keV, the magnetic field should be increased to B ₀ = 5 T.     

Magnetization and Static Magnetic Susceptibility of Fine-Crystalline High-Temperature YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Superconductors Synthesized by the Sol–Gel Method

A comparative study of the magnetization and static magnetic susceptibility of high-temperature superconductors (HTSC) YBa₂Cu₃O_y synthesized by two variants of the sol–gel method with different average sizes of crystallites 〈 D〉 ranging 0.4–2 μm has been performed in constant magnetic fields (Н ≤ 6 kOe). It has been shown that the different annealing temperatures and times, at which their crystal structure is formed, change both the average sizes of crystallites 〈D〉 and the sizes of the structural homogeneity regions 〈l〉 and, at the same time, the magnetic field penetration depth (λ) and the coherence length (ξ). As a result, such parameters as 〈D〉 ~ λ and 〈l〉 ~ ξ become comparable, leading to a change in the physical characteristics of HTSCs. It has also been shown that the superconducting transition temperature T_c determined from the measurements of magnetic characteristics in constant magnetic fields remains within values optimal for superconductivity (T_c ≈ 92 K) in the case of an optimal number (y) of oxygen atoms, which determine the levels of charge doping for a given compound.     

High field magnetization of NdAl2 single crystals interpreted with crystal field theory

The magnetization of NdAl₂ single crystals was measured at 4.2, 20.3 and 77 K, in magnetic fields up to 35 tesla applied in the 〈100〉, 〈110〉 and 〈111〉 directions. The magnetization in these directions may be described theoretically, without any fitting, in terms of two cubic crystalline electric field parameters and one molecular field constant which have been taken from inelastic neutron scattering data.⁵     

Fe39.4－xCo40Si9B9Nb2.6Cux纳米晶合金的有效磁各向异性研究

采用多晶材料趋近饱和定律研究了非晶Fe_39.4-xCo₄₀Si₉B₉Nb_2.6Cu_x(x=0.5,1,1.5) 合金在不同温度纳米晶化后的有效磁各向异性常数〈K〉.结果表明， Cu含量较低(x=0.5)时，纳米晶粒较大并且在较低的退火温度(550℃)下析出硬磁相，〈K〉随退火温度T_a升高显著增加；随着Cu含量的增加，有效地细化了晶粒，并且抑制了硼化物的析出，〈K〉明显减小.讨论了〈K〉与晶粒尺寸D及初始磁导率的关系. 关键词： 纳米晶 有效磁各向异性 磁导率 FeCo基合金     

Anomalous shape of cyclotron resonance line in n-GaP in high magnetic fields

Cyclotron resonance in n-GaP has been observed at 119 μm in pulsed magnetic fields up to 410 kG. From the experiments with the magnetic field parallel to the 〈100〉, 〈110〉 and 〈111〉 axes, it is concluded that the transverse effective mass for electron is and that the anisotropy factor of the conduction band is K = 7.9^+3.2_?2.0. An anomalous shape of the absorption curve was found in the magnetic field directions parallel to the crystal axes 〈110〉 and 〈111〉.     

High field magnetisation and hall effect of U3Sb4 single crystals

We have examined the Hall effect of U₃Sb₄ (T_c = 146 K) in the paramagnetic and ferromagnetic ranges as well as the magnetisation along three principal directions at 4.2 K and in fields up to 35 T. Both ordinary and extraordinary Hall constants are positive, giving the hole concentration of 1.2 × 10²⁰ cm⁻³. The easy magnetic axis was found to be 〈100〉, and the uranium moment was determined to be 2μ_B. Magnetisation jumps at 4.9 and 17.6 T in fields along the 〈111〈 and 〈110〉 direction, respectively, were also found. A microscopic spin model including crystal-field and anisotropic-exchange interactions predicts magnetisation behaviour in qualitative agreement with that observed experimentally for U₃X₄ (X = P, As, Sb) compounds, and it shows that the observed jumps are spin-orientational transitions.     

Investigation on the magnetocaloric effect in DyNi2, DyAl2 and Tb1−nGdnAl2 (n=0, 0.4, 0.6) compounds

The magnetocaloric effect (MCE) in the DyNi₂, DyAl₂ and Tb_1−nGd_nAl₂ (n=0, 0.4, 0.6) was theoretically investigated in this work. The DyNi₂ and DyAl₂ compounds are described considering a model Hamiltonian which includes the crystalline electrical field anisotropy. The anisotropic MCE was calculated changing the magnetic field direction from 〈1 1 1〉 to 〈0 0 1〉 in DyNi₂ and from 〈1 0 0〉 to 〈0 1 1〉 in DyAl₂. The influence of the second- and first-order spin-reorientation phase transitions on the MCE that occurs in these systems is discussed. For the calculations of the MCE thermodynamic quantities in the Tb_1−nGd_nAl₂ systems we take into account a two sites magnetic model, and good agreement with the available experimental data was obtained.     

Magnetization anisotropy in the AFM and SDW phases of CeB6

The angular dependences of the magnetization and Hall resistance have been investigated by the method of the sample rotation in the magnetic field in the high-quality single-crystal samples in the paramagnetic and magnetically ordered phases of CeB₆ in the magnetic field up to 60 kOe. It has been shown that, as CeB₆ undergoes the transition from the antiferromagnetic modulated phase to the so-called antiferroquadrupolar phase, the easy-magnetization axis in the [110] plane changes from 〈100〉 to 〈110〉. The magnetic field dependences of the anisotropic component of the magnetization differ radically in these magnetically ordered phases. The analysis provides evidence in favor of the formation of a state with the spin density wave (SDW phase) in the temperature range T _N ≈ 2.3 K < T < T _Q ≈ 3.3 K in CeB₆.     

Large magnetic anisotropy in single crystal us

It is shown for ferromagnetic US that an extremely large anisotropy restrains magnetic moments to 〈111〉 easy axes, resulting in a near cos θ angular dependence of the magnetization away from the 〈111〉 axes. This is further confirmed by torque measurements, which in addition show large hysteresis effects upon rotation through the hard axes. It is illustrated through torque and magnetization measurements that a near stable domain configuration can be established by field rotation through decreasing angular amplitude around a hard 〈001〉 direction. The anisotropy constant K₁(T) is estimated by computing the small angle through which the magnetization deviates from the 〈111〉 axes when a field is applied along the [001] direction.     

Neutron diffraction study of single crystal europium in an applied magnetic field

A single crystal of europium has been studied in applied magnetic fields up to 41.7 koe. At T_N = 90.5 ± 0.5°K a first order magnetic transition is observed. At 4.2°K the effect of an applied magnetic field in either a 〈100〉 or 〈110〉 direction is to stabilize a helix structure having τ along the field direction. This field stabilized structure remains even if the field is reduced to zero. The hysteresis associated with these transformations has been investigated and is discussed. No ferromagnetic components have been detected in fields up to 41.7 koe.     

Farbzentren rhombischer und monokliner Symmetrien in NaF

A number of zero-phonon absorption lines ofF aggregate color centers is studied inx-irradiated NaF crystals under uniaxial stress. The color centers associated with the lines are found to exhibit rhombic (D_2h, D₂, C_2v; rotation axes along 〈110〉 and 〈100〉) and monoclinic (C_2h, C₂, C_s; rotation axis along 〈110〉) symmetries. The transitions of the rhombic color centers correspond to 〈100〉 and 〈110〉 dipoles, those of the monoclinic centers to 〈112〉 and 〈110〉 dipoles. The most prominent line at 5803 Å is due to a 〈112〉 dipole transition within a monoclinic color center. Several models of centers are discussed.     

Evolution of phase,texture, microstructure and magnetic properties of Fe–Cr–Co–Mo–Ti permanent magnets

Magnetic phase evolution, crystallographic texture, microstructure and magnetic properties of Fe–28Cr–15Co–3.5Mo–1.8Ti alloy have been investigated by X-ray diffractometry, scanning transmission electron microscopy and magnetometry techniques as a function of processing conditions. Heat treatment conditions for obtaining optimum textural, microstructural and magnetic properties have been established by the experimentations. The Goss {110}〈001〉 and cube type {001}〈010〉 textures have been developed in an optimal treated Fe–28Cr–15Co–3.5Mo–1.8Ti magnets. The coercive force in Fe–28Cr–15Co–3.5Mo–1.8Ti magnets depends critically on the shape anisotropy of rod-like Fe Co Ti-rich α₁ particles and remanence on the alignment and elongation of α₁ particles parallel to applied magnetic field 〈100〉 directions. The optimum magnetic properties obtained in Fe–28Cr–15Co–3.5Mo–1.8Ti alloy are intrinsic coercive force, _iH_c, of 78.8 kA/m (990 Oe), remanence, B_r of 1.12 T (11.2 kG) and energy product, (BH)_max of 52.5 kJ/m³ (6.5 MGOe). The development of Fe–28Cr–15Co–3.5Mo–1.8Ti magnets as well as characterization of texture, microstructural and magnetic properties in the current study would be helpful in designing the new Fe–Cr–Co–Mo based magnets suitable for scientific and technological applications.     

Magnetic circular dichroism of [Co/Pd] and [CoB/Pd] multilayered films

Magnetic circular dichroism (MCD) and X-ray absorption spectra (XAS) at the Co L_2,3-edge of [Co/Pd]₂₀ and [CoB/Pd]₂₀ multilayered films, which were fabricated at 260 °C with different magnetic layer thicknesses (δ), have been measured. The lineshapes of XAS–MCD show that the electronic state of Co 3d of the films hardly changes even when sputtered at higher temperatures. The expectation values of orbital and spin angular momentum (〈L_z〉 and 〈S_z〉) are estimated using the sum rule, and it is found that 〈L_z〉/〈S_z〉 in δ<0.5 nm is larger than that in δ>0.5 nm.     

High field magnetoresistance of orientedcrystallites of AuPb2

High field magnetoresistance measurements have been made on samples of AuPb₂, which consist of islands of oriented AuPb₂ surrounded by eutectic mixture. The results obtained are very similar to what would be expected for single crystal samples. Open orbits are observed in 〈100〉, 〈110〉, 〈101〉, 〈112〉 and 〈211〉 and [001] directions. The results are consistent with predictions of the Nearly Free Electron Model.