Die Reaktion10B(d,α)8Be im Energiebereich von 0,5 bis 2 MeV

The differential magnetic susceptibility X=X′-iX″ of HoCl₃, Ho(Y)Cl₃, and Ho(La)Cl₃ has been measured with a mutual inductance bridge with frequencies from 5.3 c/s to 5.12 kc/s at temperatures between 1.1 and 4.2 °K, and in constant magnetic fields up to 3 kOe. — In monoclinic HoCl₃ a magnetic transition has been observed atT=2.15 °K (maximum of X″). No transition occurs for 0.5 and 5% Ho³⁺ in isomorphic YCl₃. — The results for nominal concentrations of 1, 2, and 5% Ho³⁺ in hexagonal LaCl₃ indicate, that there is a considerable precipitation of monoclinic HoCl₃ during crystal growth. Relaxation measurements on Ho³⁺ in hexagonal sites are interpreted in terms of a phonon-bottleneck in the temperature region 1.1 °K≦T≦2.0⁰K with a hot-phonon equilibration time of about 0.2 μs.     

Magnetocrystalline anisotropy in FeNi invar alloys under high magnetic fields

Torque measurements were made for FeNi Invar alloys at 4.2 K in high magnetic fields up to 47 kOe by using a split pair type superconducting magnet. It was found that the magnetocrystalline anisotropy constant, K₁, determined from the observed torque curves increases monotonically with increasing the field. The increasing rate, $\text{d}\text{K}{}_1\text{d}\text{H}$, was extraordinally high and could not be explained by simply considering the Zener's power law. It was suggested that some other terms, such as the Fermi-level dependent one, play an important role in this quantity.     

Antiferromagnetic resonance in ferroborate NdFe3(BO3)4

The AFMR spectra of the NdFe₃(BO₃)₄ crystal are measured in a wide range of frequencies and temperatures. It is found that by the type of its magnetic anisotropy the compound is an “easy-plane” antiferromagnet with a weak anisotropy in the basal plane. The effective magnetic parameters are determined: anisotropy fields H_a1=1.14 kOe and H_a2=60 kOe and magnetic excitation gaps Δν₁=101.9 GHz and Δν₂=23.8 GHz. It is shown that commensurate-incommensurate phase transition causes a shift in resonance field and a considerable change in absorption line width.At temperatures below 4.2 K nonlinear regimes of AFMR excitation at low microwave power levels are observed.     

Micromagnetic studies for bit patterned media above 2 Tbit/in.

Bit patterned media (BPM) recording is a candidate for extremely high density magnetic recording. A micromagnetic model is built up to analyze the phase diagram of the correct-write-in condition in BPM above 2 Tb/in.² fabricated by lithography or ion irradiation methods. The target of the study is to acquire the relationship between the recording performance and the magnetic properties of the media. The medium includes the polycrystalline grains and grain boundary. In BPM fabricated by lithography with FCT structure, two phase diagrams of the correct-write-in condition are found for the anisotropy angular distribution Δθ, the ratio of tetragonal anisotropy K₂₂ to uniaxial anisotropy K₁ and the uniaxial anisotropy distribution ΔK₁. In BPM fabricated by ion irradiation methods, two phase diagrams of the correct-write-in condition are analyzed for the ratio of saturation magnetization M′_s/M_s, anisotropy field H′_k/H_k and the exchange field H′_ex/H_ex in the ion irradiated region and the bit islands.     

Magnetic properties of CuCr2Se4 single crystals

The magnetic properties of CuCr₂Se₄ single crystals, which were grown by chemical transport reactions using iodine as a carrier, have been investigated. The magnetic moment at 0 K is found to be 5.07 μ_B per mole. The susceptibility at high temperatures follows a Curie-Weiss law with an asymptotic Curie temperature 430 K and a Curie constant 2.55 emu · $\text{deg}\text{mol}$. The magnetocrystalline anisotropy constants K₁ and K₂ are ? 6.9x 10⁵ and ? 0.9x 10⁵$\text{erg}\text{cm}{}^3$, respectively, at 5.1 K.In order to examine the effects of annealing on the magnetocrystalline anisotropy, the ferromagnetic resonance at room temperature was measured after annealing in vacuum and subsequently in an atmosphere of Se. It is found that the absolute values of K₁ and K₂ decrease after annealing in vacuum and increase to the initial values after annealing in an atmosphere of Se.     

High-resolution electroreflectance measurements of GaAs

High-resolution surface-barrier electroreflectance measurements are reported for GaAs, taken at 4.2 K in the Schottky barrier configuration. Interference effects between the bulk and space-charge regions are seen at the n = 1 exciton line for both E₀ and E₀ + Δ₀ transitions. We calculate the value μ_T = (0.055 ± 0.008) m_e for the transverse mass of the E₁ + Δ₁ transition from Franz-Keldysh oscillations observed at high fields. The E'₀ structure is resolved into separate critical points of Γ and Δ symmetry. Threshold and broadening energies are obtained at 4.2 K for the E₀,E₀, E₀ + Δ₀, E₁, E₁ + Δ₁, E'₀ (Γ and and E₂ (Σ and X) critical points.     

Magnetic Properties of Nanoparticles Useful for SQUID Relaxometry in Biomedical Applications

We use dynamic susceptometry measurements to extract semiempirical temperature-dependent, 255-400 K, magnetic parameters that determine the behavior of single-core nanoparticles useful for SQUID relaxometry in biomedical applications. Volume susceptibility measurements were made in 5 K degree steps at nine frequencies in the 0.1-1000 Hz range, with a 0.2 mT amplitude probe field. The saturation magnetization (M_s) and anisotropy energy density (K) derived from the fitting of theoretical susceptibility to the measurements both increase with decreasing temperature; good agreement between the parameter values derived separately from the real and imaginary components is obtained. Characterization of the Néel relaxation time indicates that the conventional prefactor, 0.1 ns, is an upper limit, strongly correlated with the anisotropy energy density. This prefactor decreases substantially for lower temperatures as K increases. We find, using the values of the parameters determined from the real part of the susceptibility measurements at 300 K, that SQUID relaxometry measurements of relaxation and excitation curves on the same sample are well described.     

Theory of first order magnetization processes: Uniaxial anisotropy

The first order magnetization process (FOMP) is associated with the irreversible rotation of the magnetization vector M_s between inequivalent states. The critical field H_cr and the amplitude ΔM of the jump observed in the direction parallel to the applied magnetic field are functions of the anisotropy constants of the crystal. A complete phenomenological analysis is given for the case of uniaxial anisotropy in terms of the first three anisotropy constants K₁, K₂ and K₃, as well as in terms of the anisotropy coefficients χ_2,0, χ_4,0, χ_6,0. Computer plots of the critical parameters and the magnetic phase diagram are given together with an analytical treatment of the problem. The results give a unified view of the FOMP in uniaxial crystals and provide a method for the accurate determination of the anisotropy constants at the temperatures where the phenomenon is present.     

Surface anisotropy energy of thin amorphous magnetic films of (Gd1−xCox)1−yMoy alloys; experimental results

Surface excitations in thin amorphous (Gd_1?xCo_x)_1?yMo_y films obtained by the rf sputtering technique were studied. A microwave spectrometer at X-band was used for magnetic resonance investigation with external magnetic field rotating from perpendicular to parallel resonance orientations. The critical angle and angular dependence of the position of the surface mode and the uniform mode were determined. The Surface Inhomogeneity (SI) model was applied with symmetrical boundary conditions. The surface anisotropy energy term was assumed as a superposition of the uniaxial anisotropy term and a biaxial anisotropy term. The origin of the latter term is not known yet. We also performed the resonance experiment for different temperatures ranging from 180 to 300 K. From the experiment, the uniaxial surface anisotropy constant K′_s1 and the biaxial surface anisotropy constant K′_s2 were found as functions of the temperature; the uniaxial anisotropy energy against temperature changes the sign for y=0.02 from easy axis to easy plane while the biaxial surface anisotropy does not change its character.     

Weak ferromagnetism in LaMnO3

The magnetic properties of ( La _1-x Sr x ) MnO ₃ crystals have been studied. The ac susceptibility has been measured at frequencies ranging from 10 Hz to 1 000 Hz. The x = 0.25 crystal shows a typical ferromagnetic behaviour with a dimensionless SI susceptibility of 6 below T c = 350 K limited by the demagnetizing field. Both x = 0 and x = 0.06 crystals show very sharp peaks in and at the Néel points, 139 K and 135 K respectively. This is quite unlike the usual behaviour of an antiferromagnet. Magnetization measurements on an untwinned single crystal of LaMnO ₃ show a weak moment of at 4.2 K which is directed along the c axis. The origin of this canted antiferromagnetic structure is discussed in terms of anisotropy and of Dzyaloshinskii-Moriya interaction. It is concluded that anistropy is insufficient to explain the canted antiferromagnetism. Received 8 January 1999     

Magnetization processes of the first kind in the hexaferrite Co0.62Zn1.38W

The magnetization curves M(H) and derivatives ²M/H² of a polycrystalline textured specimen of the compound BaCo_0.62Zn_1.38Fe₁₆O₂₇ are investigated in the 100–300 K temperature range. It is shown that magnetization processes of the first kind are characteristic for this compound at temperatures below 220 K. The diagram of the magnetic state is analyzed in coordinates of the normalized anisotropy constants X=K₂/K₁ and Y=K₃/K₁. Temperature dependences of the three magnetic crystallographic anisotropy constants are computed on the basis of experimental data on the critical magnetization and the field, and hysteresis loop width.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 44–47, April, 1990.     

Spin reorientation and magnetocrystalline anisotropy of (Nd1−xDyx) Fe14B

Spin reorientation and magnetocrytalline anisotropy of (Nd_1−xDy_x)₂Fe₁₄B (x=0.25, 0.5, 0.75) have been studied from mangetization curves of magnetically aligned powders. In (Nd_1−xDy_x)₂Fe₁₄B, the spin reorientation temperature (T_SR) decreases linearly on increasing Dy-substitution from 135 to 56 K with the ratio of ΔT_SR=−1.11 K/Dy at% in the composition range of 0⩽x⩽0.75. The spin reorientation angle at 4.2 K decreases on Dy-substitution from 30.4° at x=0 to 14.7° at x=0.75. From the investigation of the magnetocrystalline anisotropy at 4.2 K, the disappearance of the spin reorientation for compositions x≳0.85 is expected.     

Magnetic properties of erbium iron garnet in high magnetic fields up to 150kOe

The magnetic properties of single crystals of erbium iron garnet (ErIG) were studied in applied fields up to 150kOe between 1.4 and 300K. At low temperature, the macroscopic easy direction of the bulk magnetization is [100]; below the compensation temperature (80±2K), the magnetization presents non-linear field evolution. On the assumption of an isolated ground doublet, the anisotropy constantsK _i (i=1,2) of ErIG are given byK _i (Er)+K _i (YIG); theK _i are calculated as a function of theG andg tensor components. It is worthwhile noting that theK _i (Er) are strongly temperature dependent; so at low temperature the anisotropy of the garnet is determined by the rare earth ions, while in the 50 K regionK ₁(Er) becomes comparable toK ₁(YIG) with the opposite sign which results in a very weak anisotropy of the garnet. Above 50 K,K ₁(YIG) is predominant and the Fe³⁺ ions determine the garnet anisotropy.     

Superconductivity and spectroscopy of heterofullerides Rb<Subscript>2</Subscript>MC<Subscript>60</Subscript>, K<Subscript>2</Subscript>MC<Subscript>60</Subscript>, and KM<Subscript>2</Subscript>C<Subscript>60</Subscript> (M = Mg,Be)

A series of new heterofullerides with compositions Rb₂MC₆₀, K₂MC₆₀, and KM₂C₆₀ (M = Mg, Be) have been synthesized. Measurements of the temperature dependences of the magnetic susceptibility in the temperature interval from 4.2 to 300 K reveal a superconducting transition in heterofullerides K₂MgC₆₀, KMg₂C₆₀, K₂BeC₆₀, and Rb₂BeC₆₀ at temperatures T _c = 13–22 K. The electron states with uncompensated spin are studied by the electron paramagnetic resonance technique. The contributions of conduction electrons and localized electrons to the paramagnetic susceptibility are extracted.     

AC susceptability and static magnetic properties of AN Fe3O4 ferrofluid

A study of a diester based Fe₃O₄ ferrofluid has been made over a wide temperature range, 4.2 K < T < 380 K, using static magnetic and ac susceptibility measuring methods. Analysis of the data yields information on the anisotropy constant, grain size distribution and clustering of the particles in the ferrofluid.     

Study of ferrofluids by Mössbauer spectroscopy

The parameters of the log‐normal size distribution of a MnFe₂O₄ ferrofluid powder sample have been determined by X‐ray diffraction. The mean blocking temperature was determined from the maximum of _Xi . Mössbauer spectra at 4.2–300 K are interpreted by a new simple theory of superparamagnetism and taking a reduction of the internal magnetic field for small particles, a size dependence of the anisotropy constant, the size distribution and collective excitations into account.     

R2Fe14B(R=Ce,Pr,Gd)磁晶各向异性常数K1,K2随温度的变化

本文在1.5—300K温度范围内测量了R₂Fe₁₄B(R=Ce,Pr,Gd)各向异性常数K₁,K₂和各向异性场H_A随温度的变化。同时用单离子模型计算了Pr³⁺离子对Pr₂Fe₁₄B磁晶各向异性的贡献,得到与实验值半定量符合的结果。 关键词：     

Muon Knight shift in palladium

The Knight shift at positive muons implanted in pure palladium has been measured as a function of temperature from 19.8 to 883 K. The Knight shift variation is strictly proportional to the Pd magnetic susceptibility with ΔK^μ/Δ_x=-(0.43±0.02) mole/emu=-(2.39±0.11)kG/μ_B. A temperature independent term K^μ(x=0)=+45±10 ppm is found. The results are discussed in terms of the electronic structure of H in Pd.     

A method for determination of higher-order magnetic anisotropy constants — Importance of the cubic K3 and K4 for certain energy levels models

A method for determination of magnetocrystalline anisotropy constants of arbitrary order is proposed. The method is based on a least squares fitting of a phenomenological anisotropy energy for a given symmetry truncated at an arbitrary order term to a theoretical anisotropy energy computed exactly for a given energy level model. Several applications of the method to cubic systems are considered. The study reveals that the widely used expressions in the literature for the cubic constants K₁ and K₂ in terms of free energy for the three symmetry direction are of rather limitedvalidity only. The higher-order cubic constants K₃, K₄ and K₅ are determined besides the usual K₁ and K₂ in temperature range 0 to 300 K. The importance of the higher- order terms with respect to the first term in the cubic anisotropy energy is discussed. The results show that the cubic constants K₃ and K₄ cannot be neglected for most of the energy level models studied at certain temperatures.     

Nonleptonic Interactions of Kaons in the Quark Confinement Model

Nonleptonic, electromagnetic decays of K-mesons and K°–K̄° transition are treated with the effective Hamiltonians with ΔS = 1, 2. Matrix elements of four-quark operators are calculated in the framework of Quark Confinement Model. The account of the intermediate scalar mesons turns out to allow to explain ΔI = 1/2 rule. The account of intermediate scalar and pseudo-scalar states leads to experimental value of mass difference of K_L°–K_S° mesons. The obtained values for nonleptonic and electromagnetic decay widths as well as mass difference Δm_LS are in good agreement with experimental data.