Showing papers on "Magnetic anisotropy published in 1977"

An analysis for the magnetization mode for high density magnetic recording

Abstract: By the analysis of the self-consistent magnetization and the direct observation of the remanent magnetization of a real tape, the authors discussed the obstacles which are, and will be, encountered in attaining a higher recording densities with the present magnetic recording system, which uses mainly a longitudinal magnetization mode. Then the properties of the three magnetization modes (longitudinal, circular, and perpendicular) are compared. The mode transformation is also discussed. Finally a new perpendicular magnetic recording system is proposed for high density recording. And some results of fundamental experiments are presented. The system uses the perpendicular magnetization mode which is basically free from the demagnetization in very high densities. Its realization mainly owes to the development of a perpendicular anisotropy film and perpendicular magnetic heads.

Magnetic anneal anisotropy in amorphous alloys

Abstract: The uniaxial magnetic anisotropy K u induced by a magnetic anneal has been determined, after stress relief, for a series of alloys given by (Fe y Ni 1-y ) 80 B 20 . For all of these alloys K u depends on anneal temperature as predicted by directional order theory. The concentration dependence of K u in these alloys is also consistent with directional order theory. The maximum K u , corrected for its temperature dependence, occurs at the composition y = 0.5 . However, K u does not fall to zero at y = 1 as predicted if directional order is assumed to arise only from Fe-Ni pair ordering. These results are interpreted as suggesting a role of the glass former, boron, in the directional ordering, perhaps as an "interstitial." The interaction energy derived from the results is negative as expected for interactions leading to precipitation. Its large value of \approx -7.5 \times 10^{-14} ergs corresponds to a critical temperature for precipitation of 3000 K.

Superparamagnetic and ferrimagnetic resonance of ultrafine Fe3O4 particles in ferrofluids

Abstract: Coated ultrafine magnetite particles (average diameter around 100 A) in five nonmagnetic liquids (commercial ’’ferrofluids’’) have been investigated by electron magnetic resonance at room temperature. A narrow signal can be attributed to the superparamagnetic fraction of the particles. A simple ’’superparamagnetic narrowing’’ model is consistent with the measurements. The ferromagnetic fraction gives a broad line. Both lines narrow upon dilution because the interparticle dipolar interaction is reduced. Variations of the viscosity have only minor effects on the signals. Dilution in trifluoroacetic acid seems to destroy the coating. The resulting agglomeration and sedimentation changes the magnetic resonance drastically. The reasons for the high value of the cubic anisotropy constant K1? (−5.8×105 erg/cm3) found for the ultrafine particles are discussed.

Changes in Curie temperature, physical dimensions, and magnetic anisotropy during annealing of amorphous magnetic alloys

Abstract: We have measured the effects of annealing in air on various properties of several amorphous alloys. Reported here are results on the changes in Curie temperature, in the physical dimensions of lengths of amorphous ribbon, and in the magnetic anisotropy. Increases in Curie temperature up to 35°C have been measured. All the alloys examined show a steady increase in T c on annealing at low temperatures, but some compositions show a smaller increase in T c on annealing near the crystallization temperature than on annealing at lower temperatures. There appear to be two competing mechanisms influencing T c . All the alloys examined show a clearly measurable decrease in length on annealing; we interpret this as an increase in bulk density. The kinetics of the annealing are similar to those of the stress relaxation. Finally, annealing experiments on the shape of 60 Hz hysteresis loops show a decrease in the anisotropy associated with non-uniform internal stresses, but in some cases also show the slow development of a fairly strong uniaxial anisotropy with its easy axis perpendicular to the ribbon axis. This uniaxial anisotropy is tentatively ascribed to the development of an oxide layer during annealing, which in turn produces a uniform compressive stress due to differential thermal contraction and therefore a stress-magnetostriction anisotropy. The changes in Curie temperature and in sample dimensions cannot be ascribed to oxidation. All the results described above are for annealing treatments that do not cause crystallization. The time for crystallization at various temperatures has been measured, and activation energies for crystallization derived.

Anomalous thermal expansion and magnetostriction of single crystal Tb .27 Dy .73 Fe 2

Abstract: Single crystal magnetostriction and thermal expansion measurements are reported on Tb 27 Dy 73 Fe 2 A spin reorientation at T = 283K causes the sudden onset of a very large magnetostrictive distortion which yields a huge anomalous contribution to the linear thermal expansion The temperature and magnitude of this contribution is field controlled The expansion coefficient d(\Delta\ell/\ell)/dT can be varied from +5 to +115×10-6/°K Normal magnetostrictive behavior is observed above 283K Below this temperature a change in the easy axis from the highly magnetostrictive [111] axis to the weakly magnetostrictive [100] direction causes an anomalous field dependence Here large external fields are required to saturate the moment along [111]

Spin‐wave resonance spectra of inhomogeneous bubble garnet films

Abstract: Spin‐wave resonance at 10 GHz has been observed in thin (? 5 μm) garnet films of approximate composition Y2.85La0.15Fe3.75Ga1.25O12. The films were grown by LPE on [111]‐oriented gadolinium gallium garnet substrates, both from a nonstirred melt (vertical mode of dipping) and a stirred melt (horizontal dipping, applying axial substrate rotation). The spectra exhibit large numbers of strongly excited modes with large deviations from quadratic spacing, which are interpreted in terms of a volume inhomogeneity of the uniaxial anisotropy constant Ku. Two models are used to explain the experimental spectra. In one model the film is considered as being built up of exchange coupled layers having different uniaxial anisotropy constants Ku. In the second model it is assumed that Ku varies linearly with the distance from the substrate, but with different slopes in different regions. No pinning is assumed at the surfaces. A simple graphical method is presented for determining the normal modes of films with these types...

Hysteresis curves and magnetization processes in a model for an amorphous magnet with random uniaxial anisotropy

Abstract: We consider the magnetic field behavior of a simple model for an amorphous ferromagnet with random single‐ion anisotropy. The spins are taken as classical unit vectors located at sites of a dense random packing model and coupled via nearest‐neighbor exchange interactions. An easy‐axis direction is chosen at random for each site. For large anisotropy, the coercivity is very large and the hysteresis curves resemble those found for amorphous TbFe2 at low temperature. As the anisotropy is reduced, there is a fairly abrupt change in the behavior of the model indicating that sufficiently weak random anisotropy is effectively averaged away. We have examined the energy of metastable states. The results indicate that the canted aligned state is always more stable than low‐moment spin‐glass‐like states. We also consider the magnetization process in the presence of imposed domain walls and find that wall motion is preceeded by magnetization rotation in the high‐coercivity regime.

Anisotropy effects in superconductors

Abstract: 1. The Upper Critical Field.- R-1 On the Theory of Macroscopic Anisotropy Phenomena in Type-II Superconductors.- R-2 Experimental Investigations on the Anisotropy of the Upper Critical Field in Type-II Superconductors.- 2. Hc2 and Related Properties.- C-1 The Influence of Fermi Surface Anisotropy on Hc2(T).- C-2 Impurity Dependence of Hc2 Anisotropy in Niobium.- C-3 Microscopic Anisotropy Parameters of Niobium.- C-4 Anisotropy of Hc2 in PbTl-Alloys.- C-5 Comments on Hc2 at Low Temperatures.- C-6 The Influence of Magnetic Anisotropy on the Properties of Niobium in the Mixed State.- C-7 Anisotropy of the Stress Dependence of Critical Parameters in Uniaxial Superconductors.- 3. Flux Lines.- R-3 Magnetization and Flux Line Lattice in Anisotropic Superconductors.- R-4 Morphology of Flux Line Lattices in Single-Crystalline Type-II Superconductors.- 4. Flux Lines, Domains and Magnetization.- C-8 Correlations between Flux Line Lattice and Crystal Lattice.- C-9 Experiments on the Correlation between the Flux Line Lattice and the Crystal Lattice in Superconducting Lead Films.- C-10 Anisotropy in the Intermediate State of Superconducting Mercury.- C-11 Mixed State Anisotropy of Superconducting Vanadium.- C-12 Measurement of Torque due to Anisotropy of the Magnetization Vector in Superconducting Niobium.- 5. Energy Gap.- R-5 Microscopic Calculations of Energy Gap Anisotropy.- R-6 An Evaluation of the Validity of Superconducting Evidence for Anisotropy and Multiple Energy Gaps.- 6. Energy Gap and Related Properties.- C-13 Tunneling Junction Phenomena: An Answer to Unanswered Questions.- C-14 An Analysis of Evidence for Superconducting Energy Gap and Pairing Interaction Anisotropy for Two Types of Experiments.- C-15 A Nearly Free Electron Model of the BCS Gap Equation: Energy Gap Anisotropy in Gallium.- C-16 Specific Heat of Superconducting Zinc.- 7. Other Topics.- C-17 Unusual Resistance Effect Shown in a Periodic S-N-S System (Pb-Sn Lamellar Eutectic).- C-18 The Upper Critical Field of Superconducting Polysulfur Nitride, (SN)x - (Abstract only).- List of Participants.- Author Index.

The microstructure of amorphous rare-earth/transition-metal thin films

Abstract: An anisotropic microstructure has been discovered in vapour-deposited, amorphous rare-earth/transition-metal films. The structure consists of columnar regions of from 50-200 AA in diameter that are surrounded by a network of less dense material. The authors were able to produce a perpendicular component of magnetic anisotropy in amorphous Gd-Co films by evaporation in an oxygen atmosphere of approximately 10-6 Torr.

Magnetically induced anisotropy in amorphous alloys of Fe-Ni-P-B

Abstract: The uniaxial magnetic anisotropy K u induced during magnetic annealing has been determined for a series of amorphous alloys of the formula (Fe y Ni 1-y ) 80 P 14 B 6 . In contrast to the (Fe, Ni) 80 B 20 amorphous alloys previously reported, K u in the present alloys has neither the composition dependence nor the temperature dependence predicted from simple pair order theory. The results strongly suggest the presence of a large contribution to the directional order anisotropy from the metalloids in the iron-rich amorphous alloys. The dependence of the uniaxial induced anisotropy on decreasing iron concentration can be accounted for by a decreasing contribution from the metalloids. A discrepancy in the temperature dependence of K u at high anneal temperatures is attributed to the experimental problem of too slow a quench from the anneal temperature, compared to the rather fast kinetics of equilibration at temperatures below the anneal temperature.

Magnetization of Low Temperature Phase of Fe 3 O 4

Abstract: Saturation magnetization of low temperature phase of Fe 3 O 4 was accurately measured for the monoclinic single phase using automatic magnetic pendulum. The spontaneous magnetization just below T V was found to be about 0.1% smaller than that just above T V , even after the extrapolation to the infinitely large magnetic field which is applied parallel to the cubic [001]. The saturation magnetization at 0 K was determined to be 97.77 emu/g (4.05 µ B /Fe 2+ ) after extrapolation to 0 K by using the T 3/2 law. The magnetization curves were measured along the principal axes of monoclinic phase and compared with the calculation using the available anisotropy constants. The agreement was good except for low magnetic field region in all the directions.

Different origin of the perpendicular anisotropy in amorphous Gd-Fe from Gd-Co films

Abstract: In order to contribute to the investigations of the mechanism of positive K u induced in the amorphous R-T films, a magnetic study was made on the amorphous Gd-Fe and Gd-Co films prepared under various conditions. It is found that the origin of K u in the Gd-Fe films is quite different from that in the Gd-Co ones. In the case of Gd-Co, the positive K u is known to be induced by a resputtering effect and its physical origin is thought as an atomic pair ordering. However, a different mechanism of stress induced anisotropy is taken as the responsible one for the positive K u in the Gd-Fe films.

Magnetic anisotropy in evaporated amorphous films of the ternary system Gdx(Fe1−yCoy)1−x

Abstract: Magnetic anisotropy has been determined for evaporated amorphous films of Gdx(Fe1−yCoy)1−x with 0.08

Magnetic Studies of Residual Stress in Iron and Steel Induced by Uniaxial Deformation

Abstract: The nature of the residual stress in steel after uniaxial plastic deformation was investigated magnetically. The B-H curve measured in the residual stress state after elongation was similar to the one under compressive stress, and the induced magnetic anisotropy was uniaxial with the easy axis at right-angles to the previous direction of elongation. By employing a newly developed magnetic probe, which detects the sign and the magnitude of the induced uniaxial magnetic anisotropy under deformation, the magnetic yielding phenomenon was observed at the mechanical yield point. The probe output was highest at this point, compared with that observed during the subsequent cycles of loading. These results are interpreted semiquantitatively on the basis of the microscopic stress distribution and the anisotropy of the magnetostrictive strain.

On the Magnetically Induced Anisotropy in Amorphous Ferromagnetic Alloys

Abstract: Compositional dependence of the magnetically induced magnetic anisotropy in the Fe and Co based amorphous alloys has been studied experimentally. The induced anisotropy constant is 30–60 erg/g for Fe78Si10B12 and for Co78Si10B12 but is 400–500 erg/g for (Fe1−xCox)78Si10B12 in 0.25

Computation of gravity and magnetic anomalies due to inhomogeneous distribution of magnetization and density in a localized region

Abstract: Analytical expressions in the form of a convolution of two functions have been derived for the gravity and magnetic anomalies due to inhomogeneous distribution of magnetization and density in a localized region. These expressions show explicitly that the anomalies are completely determined by the divergence of magnetization and the first vertical derivative of density. It is thus analytically established that when a body with uniform magnetization or density is considered, the impulsive change in the physical property of the rock mass at the boundary of the body is responsible for generating an anomalous magnetic or gravity field. These properties are utilized to derive efficient algorithms for computing gravity and magnetic anomalies. An example is given to demonstrate the usefulness of the derived algorithm in computing the anomaly due to magnetization of an irregularly shaped topography.

Domain wall size and magnetic losses in frequency spectra of ferrites and garnets

Abstract: It is shown that the value and the frequency of losses in susceptibility spectra follow the relation established by Globus : the value of μ" is proportional to the mean grain size D m , the relaxation frequency is proportional to 1/D\min{m}\max{2} . Curves obtained from series of NiFe 2 O 4 and YIG samples with various D m are reduced to single curves. It has been also possible, by taking into account the specific properties (the spontaneous magnetization, the total and magnetocrystalline anisotropy fields) to reduce the final single curves for both the compositions to a single intercomposition curve of losses as a function of frequency.

Magnetic anisotropy of substituted R 2 Co 17 compounds (R = Nd, Sm, Er and Yb)

Abstract: Saturation magnetization (M s ), Curie temperature (T c ) and easy direction of magnetization have been measured on Yb 2 Co 17-x Fe x , Er 2 Co 17-x M x (M = Fe, Mn, Ni), Nd 2 Co 17-x Al x and Sm 2 Co 17-x Al x compounds. The T c and M s vary in a similar manner for all the compounds investigated. Anisotropy field variation also shows a similar trend. It is proposed that the observed variations can be used as a guide for future experiments on the substituted R 2 Co 17 compounds.

Anomalous increase of coercivity in iron oxide powder coated with sodium polyphosphate

Abstract: An anomalous increase of coercivity in a non-stoichiometric acicular iron oxide powder which was treated with a chain like sodium metaphosphate was investigated. The coercivity increased by a factor of about 2 in the acicular iron oxides and about 3 in the granular one, respectively. The magnetization decreased in inverse proportion to the increased coercivity. The coercivity of the treated iron oxides which was washed with water to remove the sodium metaphosphate returned to the value or to less than the value of the untreated iron oxides. The large magnetic anisotropy was estimated from the magnetic hysteresis loop. A constricted hysteresis loop was observed in treated iron oxides. The experiment suggests that an origin of the increased coercivity is due to the surface magnetic anisotropy which is based on the electrostatic coupling, participating in a absorbed compound.

Perpendicular magnetic anisotropy in evaporated amorphous GdCo films

Abstract: Amorphous GdCo films with strong perpendicular magnetic anisotropy were vacuum deposited by thermal evaporation of the constituents in an oxygen atmosphere of at least 3×10−8 Torr. In this paper the fabrication technique and the magnetic properties of the resulting GdCo films will be reported.

Bulk magnetic properties of the amorphous alloys RE 50 Ag 50 (Re = Gd, Tb, Dy, Ho, and Er)

Abstract: The initial susceptibility and magnetization as a function of applied field and temperatures have been measured for the amorphous alloys RE 50 Ag 50 (RE=Gd, Tb, Dy, Ho, and Er). These have been supplemented by measurement of the time dependence of magnetization. All these alloys exhibit a spontaneous magnetization at low temperatures. An order of magnitude for the magnetic anisotropy has been determined from the experimental data. The diverse phenomena responsible for magnetic ordering and the magnetic after-effect are analysed and discussed.

Thin film magnetic head

Abstract: A magnetic head for reading out the state of magnetization recorded on a magnetic recording medium, in which the magnetic head comprises a substrate of insulating material, an amorphous magnetic thin film, a pair of current terminals, and a pair of voltage terminals. The amorphous magnetic thin film is deposited on the substrate so as to have a width smaller than respective unit areas of magnetic records on a magnetic recording medium to be separately read out therefrom and to have an easy axis of magnetization in a direction perpendicular to the film surface. The current terminals are formed on the substrate for flowing a current in the amorphous magnetic thin film in the lengthwise direction thereof. The voltage terminals are formed on the substrate for deriving from the amorphous magnetic thin film a voltage induced in the transverse direction thereof.

Rotational-type spin reorientation in Nd 1-x Dy x Co 5 and its application to thermomagnetic generator

Abstract: A rotational-type spin reorientation (SR) phenomenon is found in single crystals of Nd 1-x Dy x Co 5 , and the SR temperatures are controlled by Dy concentration near room temperature In the SR temperature region an anomaly of a trapezoid shape is observed in specific heat, and it shows the second order nature of this phase transition A thermomagnetic generator utilizing this phenomenon is invented, where thermal energy is converted directly into electric energy through the magnetic flux change accompanied with the SR In an ideal case, the maximum energy that can be converted is evaluated as the magnetic anisotropy energy in the SR temperature region

Surface, catalytic, and magnetic properties of small iron particles: The effect of chemisorption of hydrogen on magnetic anisotropy.

Abstract: The superparamagnetic behavior of very small particles of metallic iron (ca 1.5 nm), with about half of their atoms at the surface, is changed reversibly by adsorption and desorption of hydrogen below the superparamagnetic transition temperature. The change after adsorption implies a lowering of the anisotropy energy barrier for the magnetic relaxation of iron and is ascribed to a change in crystalline shape. No such changes are observed for larger particles of iron (ca 8 nm) with about 10% of their atoms at the surface.