Showing papers on "Magnetization published in 1975"

Calculation of the M 23 magneto-optical absorption spectrum of ferromagnetic nickel

Abstract: The ${M}_{23}$ magneto-optical absorption spectrum of ferromagnetic nickel is calculated using an approach similar to the component state-density method that has been successfully used in obtaining valence-band emission and absorption x-ray spectra of metals. The ${M}_{23}$ magneto-optical effects result predominantly from spin-orbit splitting of the $3p$ core state in conjunction with the final $d$-state spin polarization. The calculated spectrum exhibits features that are directly related to electronic structure parameters including the $3p$ core spin-orbit splitting, and the unfilled $d$-band spin polarization. Temperature variations in the magneto-optical structure can be used to determine separately the exchange-splitting variation and spin-wave excitation contributions to the decrease in the magnetization. Experimental verification of these predictions should provide insight into the applicability of the Stoner model to ferromagnetic nickel and may be helpful in resolving some of the apparently conflicting results of other experimental probes of the spin polarization near the Fermi level in nickel.

First order transitions in ACo 2 compounds

Abstract: Some magnetic properties of ACo2 compounds, where A is a heavy rare earth metal, are shown to be related to properties of YCo2 In particular the existence of first order transitions for A=Er, Ho, Dy, but second order transitions for A=Tb, Gd, implies a special temperature dependence of the Landau parameter B which appears in the expansion of the free energy of YCo2 in powers of the magnetization B changes from negative to positive with increasing temperature and this is verified experimentally by measurements of the field dependence of the susceptibility of YCo2 at 42, 77 and 300K in field up to 150 kOe It is estimated that an applied field of about 1400 kOe would be required to produce itinerant electron metamagnetism in YCo2 and the magnetization of GdxY1-xCo2, where the 'applied' field is the molecular field due to Gd moments, is discussed from this point of view Stoner theory is used to relate the behaviour of B to the existence of a maximum in the susceptibility of YCo2 as a function of temperature

Magnetic annealing of amorphous alloys

Abstract: Amorphous alloys with nominal composition of Ni 40 Fe 40 P 14 B 6 are shown to respond to annealing in a magnetic field. Coercive forces are reduced by a factor of 10 to 50 during annealing of straight ribbons to values of 0.003 Oe, as low as ever reported for potentially useful materials. Concurrently the ratio of the magnetization in 1 Oe applied field, to saturation, increases from about 0.5 to 0.95. These changes during annealing correlate with measured stress relief changes. It thus appears that most of the strain-magnetostriction contribution to the anisotropy is removed during annealing. Magnetic annealing at temperatures as low as 100°C results in noticeable changes in properties. From measurements transverse to the magneticaliy induced anisotropy axis, the induced anisotropy is calculated to be about 800 ergs/cm3, considerably smaller than obtained in crystalline Ni 50 Fe 50 . This field-induced anisotropy is reversible in direction and magnitude by reheating the sample to its Curie temperature and then cooling in a field. Annealing of 1.5 cm diameter toroids, made from 50 μm thick tapes, increases the initial permeability by more than a factor of 10 and decreases losses by more than a factor of 10. Losses and permeabilities after heat treatment compare favorably to the Permalloys with similar saturation magnetizations.

Linear transformations of gravity and magnetic fields

Abstract: The spectral representation of gravity and magnetic fields shows that the mathematical expressions describing these fields are the result of convolution of factors which depend on the geometry of the causative body, the physical properties of the body and the type of field being observed. If a field is known, it is possible to remove or alter these factors to map other fields or physical parameters which are linearly related to the observed field. The transformations possible are: continuation, reduction to the pole, converting between gravity and magnetic fields, converting between components of measurement, calculation of derivatives, and mapping magnetization and density distribution, relief on interfaces, and vertical thicknesses of layers.

An analysis for the circular mode of magnetization in short wavelength recording

Abstract: It has been deduced from the analysis of recording demagnetization mechanism in magnetic recording that in short wavelengths the remanent magnetization exhibits a closed-loop structure in the recording medium. In this paper a novel experimental method is presented to confirm the existence of such structure (a circular magnetization mode) and to investigate its mechanism for usual recording medium and heads. The transformation of magnetization from a circular mode to a perpendicular mode is also discussed.

Observations of Mercury's magnetic field

Abstract: Magnetic field data obtained by Mariner 10 during the third and final encounter with the planet Mercury on 16 March 1975 were studied. A well developed bow shock and modest magnetosphere, previously observed at first encounter on 29 March 1974, were again observed. In addition, a much stronger magnetic field near closest approach, 400 gamma versus 98 gamma, was observed at an altitude of 327 km and approximately 70 deg north Mercurian latitude. Spherical harmonic analysis of the data provide an estimate of the centered planetary magnetic dipole of 4.7 x 10 to the 22nd power Gauss/cu cm with the axis tilted 12 deg to the rotation axis and in the same sense as Earth's. The interplanetary field was sufficiently different between first and third encounters that in addition to the very large field magnitude observed, it argues strongly against a complex induction process generating the observed planetary field. While a possibility exists that Mercury possesses a remanent field due to magnetization early in its formation, a present day active dynamo seems to be a more likely candidate for its origin.

Magnetization of disordered cold-worked Fe-Al alloys up to 51 at.% Al

Abstract: The magnetization and high-field susceptibility of disordered cold-worked Fe1-cAlc alloys with 0

Magnetic properties of single crystals of Gd Co 2 , Ho Ni 2 , and Ho Co 2

Abstract: Magnetic measurements which have been performed on single crystals of the Gd${\mathrm{Co}}_{2}$, Ho${\mathrm{Ni}}_{2}$, and Ho${\mathrm{Co}}_{2}$ Laves phases lead to a quantitative analysis of the crystal-field effects on energy and magnetization anisotropies. The anisotropy due to cobalt is negligible. Crystal-field parameters have been determined from the magnetization variation in intense magnetic fields. The change of easy magnetization direction observed at 14 K on Ho${\mathrm{Co}}_{2}$ corresponds to a change, with temperature, of the level scheme of the $^{5}J_{8}$ ground-state multiplet. An entropy discontinuity is associated with this transition, leading to a specific-heat anomaly. For Ho${\mathrm{Co}}_{2}$, the values of the anisotropy constants at 0 K are ${K}_{1}=\ensuremath{-}{10}^{7}$ erg/${\mathrm{cm}}^{3}$ and ${K}_{2}={10}^{9}$ erg/${\mathrm{cm}}^{3}$. The interactions in Ho${\mathrm{Ni}}_{2}$ are weak compared to crystal-field effects; when a magnetic field is applied, the anisotropy increases so much that it is no longer possible to measure it.

Simple equations for the magnetization and reluctivity curves of steel

Abstract: The normal B-H curves of several types of steel are shown to be approximated by the equation H= (k_{1} e^{k_{2}B^{2}} + k_{3}) B . The reluctivity ( H/B ) and its derivative with respect to B are given by simple equations that are especially useful in the finite element method of analyzing steel magnetic circuits.

A neutron diffraction study of the nuclear and magnetic structure of BiFeO3

Abstract: The atom positions in antiferromagnetic and ferroelectric BiFeO3 have been obtained by profile analysis of powder neutron diffraction data collected ant 42K and 293K The sublattice magnetization also determined at 42K, has been used to obtain a covalency parameter sum, Asigma 2+2Api 2+As2=134+or-05% An experiment to obtain further information about the neutron magnetic form factor, by complete separation of the nuclear and magnetic contributions using polarization analysis, is described

Ferromagnetism in lithium holmium fluoride-LiHoF4. I. Magnetic measurements

Abstract: Magnetic susceptibility measurements on LiHoF4 show that this compound undergoes a transition to a ferromagnetic state below Tc=1.53K, with the Ising-like Ho3+ moments oriented along the crystallographic c-axis. Analysis of the shape-dependent Curie-Weiss O indicates that magnetic dipole interaction dominates the ordering process.

Electric field dependence of the magnetic anisotropy energy in magnetite (Fe 3 O 4 )

Abstract: The application of a static magnetic field to a single crystal of synthetic magnetite (${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$) at 42\ifmmode^\circ\else\textdegree\fi{}K is found to induce a static electric polarization which is a nonlinear function of the components of the magnetic field and exists even in the absence of an applied electric field A newly modified thermodynamic theory shows that these nonlinear magnetoelectric effects arise from the electric field dependence of the macroscopic magnetic anisotropy energy No such dependence has been observed previously at any temperature in any material The values of the electric field derivatives of two of the anisotropy constants are determined by means of experiments in saturating magnetic fields With the use of these two values, and without the use of adjustable parameters, the modified thermodynamic theory successfully predicts the measured curves of (a) the induced electric polarization as a function of the orientation of a nonsaturating magnetic field of constant magnitude and (b) the induced electric polarization as a function of the magnitude of a sufficiently large magnetic field of constant orientation After a brief discussion of the microscopic origin of the electric field derivatives of the anisotropy constants, appropriate symmetry arguments are used in conjunction with the experimental data to show for the first time that the point group of the crystallographic space group of magnetite at 42\ifmmode^\circ\else\textdegree\fi{}K is the group 1

Mossbauer study of the intermetallic compounds (Fe1-xCox)2B and (Fe1-xCox)B

Abstract: Results of Mossbauer measurements on the intermetallic compounds (Fe1-xCox)2B(0

Platinum‐cobalt films for digital magneto‐optic recording

Abstract: Platinum‐cobalt thin films were prepared by rf sputtering with substrate biasing to contol composition. Contrary to what was expected from equilibrium bulk properties, films deposited at room temperature have the fcc structure, in‐plane magnetization, and low coercivity. At deposition temperatures above about 500 °C the coercivity increases and x‐ray analysis indicates some tetragonal phase. Annealing at 600 °C causes rapid conversion to the tetragonal phase. In the annealed state the films have a large component of magnetization normal to the film plane with typical remanence‐to‐saturation ratios of 0.8 and coercivities of 8 kOe perpendicular to the film plane. The saturation Faraday rotation of annealed films is about 5×105 deg/cm in the visible and near ir. Curie temperatures are in the range 270–430 °C for compositions with 35–44 at.% cobalt. Dynamic read‐write experiments show that this material is an attractive candidate for digital magneto‐optic recording. Problems due to the high Curie‐point and h...

Magnetocrystalline anisotropy of light rare-earth cobalt compounds

Abstract: The magnetocrystalline anisotropy constants of Y-, Ce-, Pr-, Nd-, Sm- and CeMMCo5 were determined from magnetization and torque curve measurements on single crystals in the temperature range between 77 K and the ferromagnetic Curie point and in fields up to 16 kOe. The anisotropy of Y-, Ce-, Sm- and CeMMCo5 can be described by the constant K1 alone, whereas K2 and K4 are necessary for NdCo5 and PrCo5, for temperatures below 300 K. A comparison of the temperature dependence of K1 with the classical temperature dependence of magnetocrystalline anisotropy shows that the intrinsic anisotropy itself is a function of temperature. The change in type of anisotropy from NdCo5 and PrCo5 is consistent with crystal field calculations.

Erratum: Scaled-equation-of-state analysis of the specific heat in fluids and magnets near critical point

Abstract: Scaled equations of state for fluids and magnets are studied near the critical point, with particular emphasis on specific-heat predictions. The important of fitting both the exponent and the critical amplitudes is emphasized. Previous proposals, such as the Missoni, Levelt Sengers, and Green (MLSG) and "linear-model" equations are examined, and the corresponding amplitude ratio $\frac{A}{{A}^{\ensuremath{'}}}$ calculated as a function of the parameters. The linear model is found to be inapplicable to Heisenberg-like systems in which the exponent $\ensuremath{\alpha}$ is negative, and $\frac{A}{{A}^{\ensuremath{'}}}g1$. Specific-heat data on Xe, C${\mathrm{O}}_{2}$, Ni, and EuO are compared to predictions based on the MLSG and linear-model equations, with parameters previously determined using pressure, volume, and temperature ($\mathrm{PVT}$) and magnetization, field, and temperature ($\mathrm{MHT}$) data. There is a small but probably significant discrepancy for the fluids, and a large deviation in the magnetic case. A "modified MLSG" equation is proposed, with an additional parameter, by means of which both $\mathrm{PVT} (\mathrm{MHT})$ and specific-heat data may be fitted. Using this equation, an estimate is made for the effect of small fields on rounding the specific-heat singularity in magnetic systems. In EuO it is found that a field as small as the earth's field has a perceptible effect on the specific heat rounding near ${T}_{c}$.

The low field static susceptibility of the spin glass Au0.96Fe0.04

Abstract: New measurements in fields of less than 20 Oe of the static susceptibility of Au0.96Fe0.04 are presented. A sharp peak chi (T) is obtained under non-equilibrium conditions. When however the magnetization is allowed to come into equilibrium at each temperature, a quite different behaviour of chi (T) is found. In this particular alloy the long time equilibrium state is apparently the same as the field cooled state.

Magnetooptik und elektronische Struktur der magnetisch ordnenden Europiumchalkogenide

Abstract: The absorption coefficient and the interband Faraday rotation of EuS, EuSe and EuTe thin films have been measured as function of the photon energy (1–6 eV), the temperature (2.7–300 K) and the applied magnetic field (0–11.5 kOe). In addition a magnetic field modulation technique has been developed, with a resolution of 2 ⋅ 10−4 deg. This allows the measurement of the Faraday rotation in fields of only 100 Oe, which is important for metamagnetic samples with low critical fields. A Kramers-Kronig transformation of the Faraday rotation leads to the circular dichroism and from these two quantities and the optical constants the off-diagonal elements of the conductivity tensor have been computed. From a comparison of this experimental result with values obtained from a modified atomic model, we deduce the character of the involved transitions and the spin polarization of the occupied ground states (4f 7,p(anion)). In addition the ratio of exchange splitting to band width of the empty 5d final state can be evaluated. The fine structure of the first main peak is discussed in terms of Kasuya's coupling scheme between the 4f 6 multiplett and the excited 5d electron. In the antiferromagnetic EuTe the temperature dependence of the Faraday rotation does not follow the net magnetization of the sample for all photon energies, but some transitions show a “ferromagnetic” behavior. This is interpreted in Slater's model of the magnetic Brillouin zone.

Finite Element Modeling of Magnetic Field/Defect Interactions

Abstract: Defect modeling and the prediction of magnetic field/defect interactions is of importance to the further refinement of electromagnetic methods of defect detection and categorization. Finite element methods are particularly suited to the analysis of field distributions within magnetic structures having complex boundary geometries and nonlinear B-H characteristics. This paper describes operational aspects of the finite element technique and shows how such methods can be applied to the analysis of electromagnetic methods of nondestructive testing, by predicting the magnetic field distribution around a rectangular slot in the surface of a circular ferromagnetic bar carrying an axial magnetisation current.

Influence of the cation distribution on the magnetization of Y-type hexagonal ferrites

Abstract: Mossbauer absorption and magnetization measurements have been made in Mg2−Y and Co2−Y ferrites. The magnetizations of the various iron sublattices did not show any marked difference in Mg2−Y, whilst in the case of Co2−Y three different behaviours of the sublattice magnetizations have been detected. Low-temperature magnetization measurements in Mg2Y gave evidence of a noncollinear magnetic order. The different magnetic properties of these compounds have been explained on the ground of a preferential occupation by Mg2+ and Co2+ ions of the inner octahedral sites of the T crystallographic block. The presence in these sites of a non-magnetic ion such as Mg2+ is responsible for the peculiar magnetic order observed in Mg2−Y.

Proton‐decoupled carbon‐13 relaxation in 13CH2 and 13CH3 spin systems

Abstract: The transient behavior of the carbon magnetization in proton decoupled spectra is discussed in detail for 13CH2 and 13CH3 spin systems. The influence of multispin dipolar cross correlation effects is shown to influence the decoupled inversion‐recovery experiment and lead to a predicted biexponential recovery of the carbon magnetization. It is rationalized that for methyl relaxation, the interference effects will play an inconsequential role. However, in the methylene case, it is demonstrated that there may arise many possible instances when it will become necessary to consider these correlation effects in much greater detail. It is also shown that if (1) extreme narrowing arguments are invalid or (2) other relaxation mechanisms compete with dipolar interactions, then the NOE enhancement factors deviate from those predicted from conventional treatments. For many conceivable situations, the inferred relaxation rate will underestimate the sum of the dipolar and nondipolar contributions whereas the usage of O...

Magneto-optical and magnetization studies in the rare-earth orthochromites. IV. ErCrO$sub 3$

Abstract: Using combined Er$sup 3+$ absorption spectroscopy and bulk magnetization measurements, the magnetic properties of ErCrO$sub 3$ in the GAMMA$sub 1$, GAMMA$sub 2$, and GAMMA$sub 4$ phases have been studied as a function of temperature and external field. The experimental data are analyzed using a single-ion effective field model. For the GAMMA$sub 4$ and GAMMA$sub 1$ phases the most general Cr-Er and Er-Er coupling terms allowed by symmetry are considered and the canting angle of the ordered Cr$sup 3+$ spins (in the GAMMA$sub 4$ phase) is not constrained a priori to be temperature independent. It is concluded that the Cr-Er coupling is antisymmetric in nature and due mainly to Dzyaloshinsky-Moriya type exchange. For this type of interaction, the Cr$sup 3+$ canting angle is indeed temperature independent and this conclusion justifies the constant-canting-angle assumption used extensively in the literature. The Er- Er coupling is found to be of dipolar origin and it is shown that this interaction results in a significant temperature dependence of the effective splitting factor as deduced from optical-absorption measurements. For the GAMMA$sub 2$ phase, the data for temperatures above 20 degreeK are interpreted in terms of a constant-canting-angle model for the Cr-Er interaction. At lower temperatures it ismore » argued that the dipolar Er-Er coupling must also be considered. (AIP)« less

Relaxation and magnetic clusters in mictomagnetic copper-manganese alloys

Abstract: Quantitative data were obtained on the average giant moment and the concentration of the magnetic clusters in CuMn alloys. For aged Cu 75 Mn 25 the magnitude of the giant moment is consistent with the size of the small, atomically-ordered regions, determined by Sato et al . by means of nuclear diffuse neutron scattering. Contrary to an early model, the results do not indicate that the concentration of giant moments is measurably affected either by cooling in a magnetic field or by isothermally increasing the applied magnetic field. The relaxation of the giant moments in the applied field is responsible for most of the alternating low field susceptibility at its peak and this relaxation also gives rise to the “quasi-viscous” time-dependence of the steady field magnetization in a certain temperature range below the peak. At very low temperatures, where the relaxation effects are frozen out, it is the “quasi-elastic” response of the giant moments that is responsible for the exceedingly high steady field susceptibility.