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1.
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.  相似文献   

2.
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, dK1dH, 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.  相似文献   

3.
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 Ha1=1.14 kOe and Ha2=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.  相似文献   

4.
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 Ms/Ms, anisotropy field Hk/Hk and the exchange field Hex/Hex in the ion irradiated region and the bit islands.  相似文献   

5.
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 μB 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 · degmol. The magnetocrystalline anisotropy constants K1 and K2 are ? 6.9x 105 and ? 0.9x 105ergcm3, 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.  相似文献   

6.
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 μT = (0.055 ± 0.008) me 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.  相似文献   

7.
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 (Ms) 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.  相似文献   

8.
The first order magnetization process (FOMP) is associated with the irreversible rotation of the magnetization vector Ms between inequivalent states. The critical field Hcr 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 χ2,0, χ4,0, χ6,0. 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.  相似文献   

9.
Surface excitations in thin amorphous (Gd1?xCox)1?yMoy 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 Ks1 and the biaxial surface anisotropy constant Ks2 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.  相似文献   

10.
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  相似文献   

11.
The magnetization curves M(H) and derivatives 2M/H2 of a polycrystalline textured specimen of the compound BaCo0.62Zn1.38Fe16O27 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.  相似文献   

12.
Spin reorientation and magnetocrytalline anisotropy of (Nd1−xDyx)2Fe14B (x=0.25, 0.5, 0.75) have been studied from mangetization curves of magnetically aligned powders. In (Nd1−xDyx)2Fe14B, the spin reorientation temperature (TSR) decreases linearly on increasing Dy-substitution from 135 to 56 K with the ratio of ΔTSR=−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.  相似文献   

13.
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.  相似文献   

14.
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.  相似文献   

15.
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.  相似文献   

16.
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HA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:  相似文献   

17.
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.  相似文献   

18.
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 ΔKμx=-(0.43±0.02) mole/emu=-(2.39±0.11)kG/μB. A temperature independent term Kμ(x=0)=+45±10 ppm is found. The results are discussed in terms of the electronic structure of H in Pd.  相似文献   

19.
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.  相似文献   

20.
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 KL°–KS° mesons. The obtained values for nonleptonic and electromagnetic decay widths as well as mass difference ΔmLS are in good agreement with experimental data.  相似文献   

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