Showing papers on "Magnetic anisotropy published in 1975"

Anisotropic magnetoresistance in ferromagnetic 3d alloys

Abstract: The anisotropic magnetoresistance effect in 3d transition metals and alloys is reviewed. This effect, found in ferromagnets, depends on the orientation of the magnetization with respect to the electric current direction in the material. At room temperature, the anisotropic resistance in alloys of Ni-Fe and Ni-Co can be greater than 5%. The theoretical basis takes into account spin orbit coupling and d band splitting. Other properties such as permeability, magnetostriction, and Hall voltage have no simple relationship to magnetoresistance. Anisotropic magnetoresistance has an important use as a magnetic field detector for digital recording and magnetic bubbles. Such detectors because of their small size are fabricated using thin film technology. Film studies show that thickness, grain size, and deposition parameters play a significant role in determining the percentage change in magnetoresistance. In general, the change is smaller in films than bulk materials. Several tables and graphs that list bulk and film data are presented.

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.

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.

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

Giant Magnetically Induced Changes in the Elastic Moduli in Tb .3 Dy .7 Fe 2

Abstract: Abstract : In the report the authors discuss increases in sound velocity of greater than 60% upon magnetization of highly magnetostrictive Tb(x)Dy(1-x)Fe2, where x approximately equals 0.3. This change corresponds to a Young's modulus increase (delta E Effect) of about 160%, by far the largest known. (Modified author abstract)

Magnetic measurements on particles in suspension

Abstract: Acicular magnetic particles up to about 25 nm thick can be suspended permanently and individually in a liquid. Their orientation by dc and ac magnetic fields can be followed through the induced optical birefringence (Cotton-Mouton effect). Analysis of the field dependencies yields the average magnetic dipole moment of the particles and the width of the distribution, the magnetic anisotropy field, and the distribution of switching fields.

Field heat treatment of ferromagnetic metallic glasses

Abstract: The magnetic properties of zero magnetostrictive metallic glass have been investigated using both standard fluxmeter methods and domain patterns obtained from a scanning electron microscope technique. This investigation shows that the material is not magnetically isotropic but rather has preferred directions of magnetization that are determined by the details of the quenching process. The magnetic aniostropy produced by subsequent field anneal dominates the original anisotropy and determines the magnetic behavior after the heat treatment.

Domain wall structures in thin magnetic films

Abstract: A review of recent theoretical experimental results on domain walls in thin magnetic films both of prallel anisotropy (permalloy films) and of perpendicular anisotropy (bubble film) is given. For the case of parallel anisotropy good agreement is achieved between theoretical predictions and experimental observations of the three wall types, symmetric and asymmetric Neel walls and asymmetric Bloch walls. We show pictures of asymmetric Neel walls in NiFe single crystal foils. In general, the calculation of a domain wall in a thin film means the calculation of a two-dimensional vector field of unit length under the influence of a long-range, dipolar interaction. Theoretical methods to do this are still clumsy and only very few rigorous calculations have been published. Even models Which avoid the dipolar interaction (stray field free models) cannot be computed straightforwardly. Recent efforts are reviewed together with a proposal for a new approach.

Influence of the degree of inversion on magnetic properties of MnFe 2 O 4

Abstract: The cation distribution of single crystal manganese ferrites Mn 1-y Fe y [Mn y Fe 2-y ]O 4 with 0.06 \leq y \leq 0.24 was modified by appropriate heat treatment at temperatures 300-600°C. With these samples the Curie temperature, the magnetocrystalline anisotropy, the spontaneous magnetization and the differential susceptibility at high magnetic fields were studied. The experiments enabled us to determine the magnitude of the molecular field coefficient N Mn(A)-Fe(B) = 89 and to estimate the main part of the contribution to the magnetocrystalline anisotropy in MnFe 2 O 4 which was found to come from Fe3+in octahedral sites. High field susceptibility measurements confirmed the applicability of the noncolinear arrangement of magnetic moments in MnFe 2 O 4 which supposes that Mn(B) spins make an angle of 53° with the direction of the total magnetization.

Spin Waves in Terbium: I. Two-Ion Magnetic Anisotropy

Abstract: The energies of spin waves propagating in the $c$ direction of Tb have been studied by inelastic neutron scattering, as a function of a magnetic field applied along the easy and hard directions in the basal plane, and as a function of temperature. From a general spin Hamiltonian, consistent with the symmetry, we deduce the dispersion relation for the spin waves in a basal-plane ferromagnet. This phenomenological spin-wave theory accounts for the observed behavior of the magnon energies in Tb. The two $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}$-dependent Bogoliubov components of the magnon energies are derived from the experimental results, which are corrected for the effect of the direct coupling between the magnons and the phonons, and for the field dependence of the relative magnetization at finite temperatures. A large $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}$-dependent difference between the two energy components is observed, showing that the anisotropy of the two-ion coupling between the magnetic moments in Tb is substantial. The $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}$-dependent anisotropy deduced at 4.2 K is of the same order of magnitude as the isotropic part, and depends strongly on the orientation of the moments in the basal plane. The rapid decrease of both the axial- and the basal-plane anisotropy with increasing temperatures implies that the two-ion coupling is effectively isotropic above \ensuremath{\sim} 150 K. We present arguments for concluding that, among the mechanisms which may introduce anisotropic two-ion couplings in the rare-earth metals, the modification of the indirect exchange interaction by the spin-orbit coupling of the conduction electrons is of greatest importance.

Sound velocity in a magnetic fluid

Abstract: A simple linearized hydrodynamical theory for magnetic fluids in the presence of a strong external magnetic field is presented. The equations are solved for a sound wave propagating at angle phi from the external field direction. The sound velocity is shown to be anisotropic, depending on phi . The anisotropy is estimated to be about 10-5 for a field of 104 G and shows an interesting frequency dependence.

Magnetic Anisotropy of CoS2–Torque and NMR Measurements

Abstract: The magnetocrystalline anisotropy of CoS 2 has been measured by torque method using a single crystal and the anisotropy constants determined as K 1 <0 and K 2 ≃0, with the easy axis of [111]. The temperature dependence of K 1 is found to be proportional to the 20-th power of the thermomagnetic curve. The Co 59 NMR has been studied by both CW and transient techniques in the temperature range of 4.2–77 K. The NMR spectrum is broadened by an anisotropic hyperfine interaction, and the isotropic and axial components of the hyperfine field are determined to be -59.43 kOe and -5.42 kOe at 4.2 K. The overall resonance spectrum is explained qualitatively from the domain structure with the shape anisotropy. Some discussion of the electronic origin of the magnetic anisotropy is given.

Magnetic Properties and Magnetic Structure of ThMn2Si2 and ThMn2Ge2

Abstract: ThMn2Si2 and ThMn2Ge2 were studied using neutron diffraction, X-ray diffraction, and magnetometric techniques. Both the compounds have tetragonal CeAl2Ge2-type structure. Position parameters z for Si and Ge were determined. ThMn2Si2 is an antiferromagnet with a Neel temperature of 483 K, and ThMn2Ge2 exhibits a small ferromagnetic moment of 0.35μB with the Curie temperature of 400 K. The magnetic transition in ThMn2Ge2 is of first order. The magnetic structures for both compounds consist of ferromagnetic layers perpendicular to the c0-axis which are antiferromagnetically coupled to adjacent layers. The magnetic moment direction in ThMn2Si2 is parallel t o the c0-axis, and in ThMn2Ge2 the magnetic moment is slightly deviated from c0-axis. It is suggested that conduction. [Russian Text Ignore]

Spin waves in terbium. III. Magnetic anisotropy at zero wave vector

Abstract: The energy gap at zero wave vector in the spin-wave dispersion relation of ferromagnetic. Tb has been studied by inelastic neutron scattering. The energy was measured as a function of temperature and applied magnetic field, and the dynamic anisotropy parameters were deduced from the results. The axial anisotropy is found to depend sensitively on the orientation of the magnetic moments in the basal plane. This behavior is shown to be a convincing indication of considerable two-ion contributions to the magnetic anisotropy at zero wave vector. With the exception of the sixfold basal-plane anisotropy of the unstrained lattice, the dynamic anisotropy parameters deduced from our results agree with macroscopic measurements both with respect to the magnitudes (at zero temperature) and the temperature dependences. The deviations observed cannot be explained by existing theories which include the effects of zero-point deviations from the fully aligned ground state, and we tentatively propose polarization-dependent two-ion couplings as their origin.

High-performance anisotropic plastics magnet and a process for producing the same

Abstract: An anisotropic plastics magnet having a maximum energy product (BH)max not lower than 0.9 MG Oe, a remanence Br not lower than 2000G and a coercive force Hc not lower than 1800 Oe, and being composed at least one of ferromagnetic powders having a large magnetic anisotropy constant and at least one selected from the group consisting of metal-cross-linked copolymers of α-olefin and α,β unsaturated mono- or dicarboxylic acid and saponified copolymers of ethylene and vinyl acetate, the axis of the easy magnetization of said ferromagnetic powders being oriented substantially in one direction, and a process for producing the same comprising mixing the ferromagnetic powder and the resin and forming the mixture under heating while a magnetic field is being applied.

Texture and magnetic properties in Fe-Si steel

Abstract: In this work we have attempted to rationalize magnetic torque data by employing the crystal orientation distribution function and the formula for the anisotropy of energy for a single crystal of cubic symmetry Three kinds of magnetic material of different texture were analyzed For each of these materials (110), (200) and (112) pole figures were measured by neutron diffraction and the orientation distribution functions were determined The series coefficients of the pole figure were used for the theoretical evaluation of the torque curve Torque curves measured with a magnetometer, were compared with the results from texture data Agreement is good both qualitatively and quantitatively for all specimens

The magnetization process in hexagonal ferromagnetic and ferrimagnetic single crystals

Abstract: Neel's 'theory of phases' is used to study the magnetization process in hexagonal ferromagnetic and ferrimagnetic single-crystal ellipsoids for which the six fold contribution to the magnetocrystalline anisotropy cannot be neglected. Simultaneous equations are presented, the solution of which yields the intensity and orientation of the mean sample magnetization and the various orientations of the saturation magnetization in the domains, for all values and orientations of the magnetic field. In some cases, the fractional contents of different types of domain can also be determined. Detailed consideration is given to the three special cases of oblate spheroids the minor ellipsoidal axes of which are parallel to the principal hexagonal axes when the magnetic field is in the plane of the sample. In addition, it is shown that the magnetization process is simplified for a number of special cases in which the magnetocrystalline anisotropy assumes particularly good simple forms. A comparison of the results of the theory with the limited experimental data available is made and, as an example of the application of the theory, the magnetization of gadolinium and dysprosium is calculated as a function of the intensity and direction of the magnetic field.

Magnetic properties of amorphous magnetic alloys

Abstract: Low-field magnetic properties of amorphous ferromagnetic alloys have been previously reported mainly at d.c. The alloys in ribbon form generally show square hysteresis loops, with coercive fields less than 0.1 Oe, and with saturation magnetization up to 17000 G. Maximum magnetization is obtained in low fields only when the ribbons are under tensile stress. This paper reports further measurements on amorphous magnetic alloys, including differential scanning calorimeter data on the crystallization of three compositions and a variety of a.c. measurements on toroidal samples at frequencies up to 2000 Hz. The coercive fields and magnetic losses under a.c. excitation are disappointingly high. This is attributed to an increase in coercive field when straight ribbon is wound into toroidal form, and to a further increase in H c with frequency due to an apparent decrease in the number of domain walls participating in the magnetization reversal. Neither effect is necessarily inherent in amorphous magnetic materials.

Hartree-Fock renormalization of magnetic anisotropy in the basal-plane ferromagnets terbium and dysprosium

Abstract: The application of the Holstein-Primakoff transformation in the spin-wave theory of an anisotropic ferromagnet implies contributions from the isotropic two-ion coupling to the energy of the uniform spin-wave mode. Including these contributions, the energies of the HF renormalized spin waves are deduced using the method of Lindgard and Danielsen (1974). The macroscopic resonance theory for the uniform mode is found to agree with the spin-wave theory if the magnetization is along a symmetry direction. Numerical results for the renormalization of the static anisotropy parameters of Tb and Dy are presented. The effect of the ellipticity of the moment precession is found to be smaller than reported previously.

Effects of DC bias on the fabrication of amorphous GdCo RF sputtered films

Abstract: An investigation has been made on the effects of a dc bias field applied to Gd 1-x CO x thin films during rf sputter deposition. Such films may possess uniaxial magnetic anisotropy with easy axis perpendicular to the plane of the film and may be used in magnetic bubble devices. Uniformity in composition, thickness and magnetic properties has been achieved and film composition has been controlled to within one percent. However, significant variations of magnetic properties were observed from film to film.

Nuclear magnetic resonance of 59Co in (FE1-xCox)2B ferromagnetic borides

Abstract: Measurements are presented of the nuclear resonance frequency of 59Co in (Fe1-xCox)2B ferromagnetic borides at 4.2K for 0.1

Domain wall calculations for SmCo 5

Abstract: The structure of domain walls may be studied theoretically by considering the wall either to be a continuous magnetization distribution (micromagnetic-type approach) or a discrete moment distribution. It is shown that the discrete moment approach becomes necessary in materials of high magnetocrystalline continuous such as SmCo 5 , where the domain walls are only of the order of 10-20 atomic distances wide. The structure of such walls is found to be very sensitive to short range variations in exchange and anisotropy and the presence of an anomalous exchange interaction between two spins produces pinning fields which are of the same order as values of coercivity in SmCo 5 . It is concluded that exchange anomalies may play an important role in domain wall pinning in the rare-earth/cobalt materials and that further information on the exchange mechanisms could help to explain their high coercivities.

Pulse magnetization measurements in ferrofluids

Abstract: A pulsed-field (1 μ sec to 3 m sec) inductive magnetometer has been constructed that measures the magnetic moment of a ferrofluid as a function of time. After the applied field is removed, the magnetization is characterized by a fast decay (< 1 μ sec) and a gradual decay that can be as long as 4 msec. The fast component of magnetization varies from about 50% to nearly 100% of the total and we conclude it is due to magnetization processes within the particle. The slow component of magnetization is believed to be due to particle rotation and can be related to particle size through a model developed by Janak.

The replay signal from a tape with magnetization components parallel and normal to its plane

Abstract: A simple formula is given which describes the magnetization distribution recorded in magnetic tapes. This is more realistic than the usual M = M_{o}\sin wx in that it contains both longitudinal and normal components of magnetization. The corresponding output voltages are shown to be higher while the self-demagnetizing fields are lower than in the usual case.