Showing papers on "Magnetic anisotropy published in 1982"
01 Apr 1982
TL;DR: Magnetic anisotropy in sedimentary rocks is controlled by the processes of deposition and compaction, in volcanic rocks by the lava flow and in metamorphic and plutonic rocks by ductile deformation and mimetic crystallization as discussed by the authors.
Abstract: Magnetic anisotropy in sedimentary rocks is controlled by the processes of deposition and compaction, in volcanic rocks by the lava flow and in metamorphic and plutonic rocks by ductile deformation and mimetic crystallization. In massive ore it is due to processes associated with emplacement and consolidation of an ore body as well as to ductile deformation. Hence, it can be used as a tool of structural analysis for almost all rock types. Morcover, it can influence considerably the orientation of the remanent magnetization vector as well as the configuration of a magnetic anomaly over a magnetized body. For these reasons it should be investigated in palaeomagnetism and applied geophysics as well.
1,052 citations
TL;DR: In this paper, fine Ba ferrite particles, suitable for coated perpendicular magnetic recording media, have been prepared, about 0.08 μm in average diameter, are thin hexagonal platelets with easy magnetization axes normal to their planes.
Abstract: Fine Ba ferrite particles, suitable for coated perpendicular magnetic recording media, have been prepared. The particles, about 0.08 μm in average diameter, are thin hexagonal platelets with easy magnetization axes normal to their planes. Coercivity H c is controllable in a wide range, without significant reduction in magnetization, by Co and Ti substitution. The measured temperature dependences of H c and σ s showed stable characteristics. Good squareness ratio was obtained from an orientation capability measurement.
288 citations
TL;DR: In this paper, a theory of FMR which incorporates magnetocrystalline surface anisotropy is outlined and successfully interprets the thickness dependence of the FMR data in the ultrathin (L≲50 A) regime and shows them to be surface dominated.
Abstract: Single‐crystal {110} Fe films, grown for the first time by molecular beam epitaxy on GaAs, have been studied by a variety of techniques in order to determine the dependence of the magnetic properties upon film thickness L and quality, and an overview of these results is presented. The dependence of the ferromagnetic resonance (FMR) field upon its orientation in the (110) plane was measured at 16.4 GHz and shows that the magnetically easy axis is [110] for L<50 A and [001] for L≳150 A. A theory of FMR which incorporates magnetocrystalline surface anisotropy is outlined. It successfully interprets the thickness dependence of the FMR data in the ultrathin (L≲50 A) regime and shows them to be surface dominated. FMR data at 9.2 GHz, which contain both aligned and nonaligned resonance branches, are presented as a function L. In addition, the dependence of the branches on frequency f for 8 GHz
186 citations
174 citations
TL;DR: In this article, the magnetic structure and weak ferromagnetic magnetism of Mn 3 Sn were studied by polarized neutron diffraction at room temperature and it was shown that the spin structure has a triangular configuration of inverse geometry in the c-plane and the triangle rotates opposite to the rotation of the c -plane field component.
Abstract: The magnetic structure and weak ferromagnetism of Mn 3 Sn were studied by polarized neutron diffraction at room temperature. The flipping ratio was measured for a number of Bragg reflections by rotating the crystal about the scattering vector under a magnetic field of 8 kOe applied perpendicular to the scattering vector. It was found that the spin structure has a triangular configuration of inverse geometry in the c -plane and the triangle rotates opposite to the rotation of the c -plane field component. From the analysis of the anisotropy energy it was shown that the triangle of inverse geometry is stabilized by the Dzyaloshinski-Moriya interaction and the weak ferromagnetic moment appears from the mechanism that each spin in the inverse triangle tilts slightly toward its easy axis. It was also shown that the weak ferromagnetic moment rotates just opposite to the rotation of the triangle.
150 citations
TL;DR: In this paper, an integrating magnetometer was used to measure magnetization M as a function of applied field H and tensile stress T in morphous metallic ribbons, from which was determined the magnetostriction λs.
Abstract: Amorphous metallic ribbons annealed in transverse fields have enormous magnetoelastic coupling. An integrating magnetometer was used to measure magnetization M as a function of applied field H and tensile stress T in such ribbons, from which is determined the magnetostriction λs. A simple phenomenological model of moment rotation can account for the linear dependence of M as a function of H at T below 7×105 Pa observed in Metglas 2605SC. From the model we extract λs∼27×10−6 and anisotropy K∼38 J/M3. In stressed 2605CO no linear behavior is observed. This work substantiates previous high values obtained for the coupling factor and ΔE effect.
123 citations
TL;DR: In this article, the diamagnetic anisotropy of thirteen nematic liquid crystals is measured and the critical behavior of S near the nematic-isotropic phase transition can be described by an exponent 03B2 of the order of 0.25.
Abstract: Measurements are presented for the diamagnetic anisotropy of thirteen nematic liquid crystals. As any bias in the rotation around the long molecular axis is most probably small, the results probe accurately the temperature variations of S, the degree of orientational order. The critical behaviour of S near the nematic-isotropic phase transition can be described by an exponent 03B2 of the order of 0.25. Procedures are considered to obtain the molecular magnetic anisotropy. By a systematic variation of the structure of the molecules an impression of the contributions of the various molecular groups can be obtained It turns out to be rather difficult to obtain accurate data for the molecular magnetic anisotropy. As a consequence the absolute scale of S can only be fixed with an accuracy of the order of 10 %. J. Physique 43 (1982) 361-367 FTVRIER 1982,
104 citations
TL;DR: In this paper, a pigment of Fe4N particles for magnetic recording was prepared by nitrogenizing acicular metal iron powder, and the chemical treatment needed to obtain stoichiometric Fe 4N powder was studied, and it was found that Fe 4 N powder was obtained when the Fe powder was heated at about 400°C in a mixture of H2−NH 3 (65-80 vol%).
Abstract: A pigment of Fe4N particles for magnetic recording was prepared by nitrogenizing acicular metal iron powder. The chemical treatment needed to obtain stoichiometric Fe4N powder was studied, and it was found that Fe4N powder was obtained when the Fe powder was heated at about 400°C in a mixture of H2–NH3 (65–80 vol.%). The Curie point of the powder coincided well with that of bulk Fe4N. The coercive force of Fe4N was 640 Oe, which is considerably smaller than that of the Fe powder used as the starting material. The dispersion of magnetic anisotropy was measured by a torque meter, and the decrease in the coercivity of nitrogenized iron powder was attributed to the exchange anisotropy of the surface layer.
96 citations
TL;DR: In this paper, the authors enlarged the theory of domain wall pinning to include all magnitudes of deviation of the magnetic anisotropy, magnetization Mi, and/or magnetic exchange energy, characterizing the defect for all defect widths.
Abstract: Due to the nonlinear nature of the relevant mathematical equations, previous solutions to the geometrically simple problem of pinning of a 180° ferromagnetic domain wall by a single planar defect in an infinite medium contain the approximation of small deviations in the nature of the defect material relative to the host matrix. We have enlarged the theory of such domain wall pinning to include all magnitudes of deviation of the magnetic anisotropy Ki , magnetization Mi , and/or magnetic exchange energy Ai , characterizing the defect for all defect widths. In particular, we have obtained graphs for the resultant reduced coercive force hc = HcM1/K1 , due to such domain wall pinning, as a function of the dimensionless constants F = A2M2/A1M1 and E = A2K2/A1K1 and of the defect width, as well as graphs for the maximum obtainable coercive force as a function of F and E. (Here i = 1 represents the host material and i = 2 the defect.) As an example, we discuss these results in terms of applications to the Sm2(Co,Cu,Zr,Fe)17 hard magnetic materials.
90 citations
TL;DR: In this paper, specific heat measurements on CeAl3 were described and compared to thermal expansion results on 3He and unstable-valent 4f compounds (YbCuAl, CeBe13, CeSn3, and CePd3).
Abstract: Specific heat measurements on CeAl3 are described and compared to thermal‐expansion results. At very low temperatures, the Gruneisen parameter reaches giant negative values. Comparisons are made with the properties of 3He and the unstable‐valent 4f compounds (YbCuAl, CeBe13, CeSn3, and CePd3). It is suggested that the magnetic anisotropy may play a major role.
78 citations
TL;DR: In this article, a composite medium of a Co-Cr film with a soft magnetic back layer was shown by Lorentz microscopy to have a horseshoe magnetization structure.
Abstract: In a perpendicular recording system, a Co-Cr film as a medium is capable of storing very high density signals. Lorentz microscopy of 1000 kV TEM was used to observe the structure of recorded magnetizations in Co-Cr films having perpendicular anisotropy. A composite medium of a Co-Cr film with a soft magnetic back layer was shown by Lorentz microscopy to have a horseshoe magnetization structure. The stable antiparallel magnetization of transition in the Co-Cr layer determined the head-on magnetization structure of the soft magnetic back layer, which consists of a new straw-rope domain structure. The perpendicular magnetization structure of the Co-Cr film was found to consist of small domains magnetized through the film thickness which correspond to the columnar microstructure of the film. Since the intrinsic hysteresis loop of a Co-Cr film was shown to essentially have an ideal rectangular shape, it can be concluded that the Co-Cr layer of a composite film can be recorded by an ideal magnetizing process with negligible demagnetizing field at the transition.
TL;DR: In this paper, the surface anisotropy of a single crystal of Fe grown on (110) GaAs substrates by molecular beam epitaxy was investigated and the changes in the parameters describing the angular dependence of the FMR spectra upon cooling to 77 K can be explained as due to magnetostriction arising from thermally induced strain near the film interface.
Abstract: Ferromagnetic resonance (FMR) has been used to study a wide variety of very thin single crystals of Fe grown on (110) GaAs substrates by molecular beam epitaxy. Data were taken at room and liquid nitrogen temperatures for films with thicknesses L in the range 18–200 A. Due to surface anisotropy, the easy axis of the magnetization switches from [100] to [110] when L≤50 A, independent of whether the the film surface is passivated by an Al‐overcoat or has a thin Fe oxide surface layer. We suggest that this is an effective surface anisotropy arising in part from a depth dependent strain near the film‐substrate interface. The changes in the parameters describing the angular dependence of the FMR spectra upon cooling to 77 K can be explained as due to magnetostriction arising from thermally induced strains plus the temperature dependence of the cubic volume anisotropy. The FMR linewidth is shown to be a linear function of frequency in the range 5–40 GHz.
TL;DR: In this article, the magnetic properties of microcrystals are discussed on the basis of results obtained by use of M?ssbauer spectroscopy, and the anisotropy energy constants of micro-crystals of Fe, Co, Ni and Fe3O4 are found to change upon chemisorption.
Abstract: The magnetic properties of microcrystals are discussed on the basis of results obtained by use of M?ssbauer spectroscopy. Spectra of microcrystals with dimensions smaller than about 100 A are influenced by magnetic fluctuation effects such as superparamagnetic relaxation and collective magnetic excitations, and these effects allow a determination of the product of the particle size and the magnetic anisotropy energy constant. Measurements on ferromagnetic and ferrimagnetic particles as a function of applied magnetic fields allow a determination of the particle volume. The anisotropy energy constants of microcrystals of Fe, Co, Ni and Fe3O4 are found to change upon chemisorption. Spectra of small particles at low temperatures also give information on the magnetic properties of the atoms in the surface layer. These studies as well as thin film studies show that no magnetically dead layers are present at the surface of the samples. In the case of metallic iron an enhanced magnetic hyperfine field is found, in agreement with theoretical results.
TL;DR: In this article, a-SiO 2 is used for the preparation of Ba-ferrite films by means of targets-facing type of sputtering method which is very useful to prepare magnetic films at high rate without any bombardment of high energy particles such as γ-electrons and negative ions emitted from the targets and is favorable to obtain stoichiometric films of good quality.
Abstract: Ba-ferrite films have been prepared by means of Targets-Facing type of sputtering method which is very useful to prepare magnetic films at high rate without any bombardment of high energy particles such as γ-electrons and negative ions emitted from the targets and is favorable to obtain stoichiometric films of good quality. C-axis orientation of the films depends strongly on substrate temperature and crystal structure of substrate. C-axis well oriented BaM films are deposited on amorphous materials such as a-SiO 2 . The deposited films of 3000 A in thickness have ΔΘ 50 less than 1 degree, magnetic anisotropy constant of 3.2\times10^{6} erg/cc, saturation magnetization of 380 emu/cc and coercive force of 1.3 kOe. These films reveal much better c-axis orientation and surface smoothness than the films deposited by DC diode type of sputtering method and have almost the same composition as that of the targets.
TL;DR: The strong enhancement of anisotropy produced in CuMn by the addition of impurities with strong spin-orbit coupling is explained by Dzyaloshinsky-Moriya interactions as mentioned in this paper.
Abstract: The strong enhancement of anisotropy produced in CuMn by the addition of impurities with strong spin‐orbit coupling is explained by Dzyaloshinsky‐Moriya interactions. Estimates of the anisotropy have been obtained by approximate analytic methods as well as Monte Carlo studies. Although D‐M interactions seem to be dominant, we discuss some other sources of anisotropy, e.g., pseudo‐dipole and crystal‐field‐like terms.
TL;DR: The magnetization of the CoCr recording medium has been investigated by several methods as discussed by the authors, including the perpendicular hysteresis loops in the thickness range from 500 to 20,000 A. This provided evidence that the magnetization process is typefied by domain wall motion.
Abstract: The magnetization of the CoCr recording medium has been investigated by several methods. First the perpendicular hysteresis loops are analysed in the thickness range from 500 to 20,000 A. This provided evidence that the magnetization process is typefied by domain wall motion. Second the dependence of the coercivity on the film thickness has been determined. The dependence found can be explained if it is assumed, that the coercivity is caused by domain walls, impeded by the crystallite boundaries. Finally stand-still recording experiments have been performed, which confirm that magnetization takes place by the displacement of domain walls. The switching criterion in the writing process is best met by taking the field averaged over the film thickness.
TL;DR: In this article, the authors enlarged the theory of ferromagnetic domain wall pinning by defects to include large as well as small deviations of the magnetic anisotropy, magnetization, and/or magnetic exchange energy of the defect, from the host material for all values of defect width.
Abstract: We have enlarged the theory of ferromagnetic domain wall pinning by defects to include large as well as small deviations of the magnetic anisotropy, magnetization, and/or magnetic exchange energy of the defect, from the host material for all values of the defect width. In particular, we obtain results for the coercive force due to such pinning as a function of two dimensionless constants characterizing the defect and of the defect width. We also obtain results for the maximum obtainable coercive force in terms of these parameters. We discuss these results in terms of applications to the Sm2(Co, Cu, Zr, Fe)17 hard magnetic materials.
TL;DR: In this article, the effects of canting on the macroscopic magnetic anisotropy of rare-earth and transition-metal moments were investigated, and it was shown that this canting, even when small, can reduce the effective anisotropic energy by an order of magnitude from intrinsic sublattice anisotropies.
Abstract: The exchange coupling between rare-earth ($R$) and transition-metal ($T$) moments in ${R}_{x}{T}_{y}$ compounds is not so large as to hold the $R$ and $T$ moments rigidly parallel (for light rare-earth elements) or antiparallel (for heavy rare-earth elements); ionic magnetocrystalline anisotropy energy can be comparable to this intersublattice exchange Anisotropy torques and/or an external field can induce canting between the sublattice moments We show that this canting, even when small, can reduce the macroscopic effective anisotropy by a very large amount---more than an order of magnitude---from the intrinsic sublattice anisotropies Consideration of the effects of canting reconcile hitherto conflicting reports, by spin-wave scattering and moment measurements, of the magnetic anisotropies of ${\mathrm{Ho}}_{2}$${\mathrm{Co}}_{17}$ and ${\mathrm{Ho}}_{2}$${\mathrm{Fe}}_{17}$ One conclusion of our analysis is that since a huge degeneration of macroscopic magnetic anisotropy, and hence of the coercivity, comes from sublattice flexing, it seems to follow that to increase coercivity one should be trying to increase $R\ensuremath{-}T$ exchange; the ionic magnetic anisotropy is already greater than its effective value
TL;DR: In this article, the sign of the single site anisotropy of ZnMn, CdMn and MgMn was measured at millikelvin temperatures and it was shown that the Mn moments lie parallel to the $c$ axis with the easy axis in the basal plane.
Abstract: dc magnetization measurements at millikelvin temperatures on dilute ZnMn, CdMn, and MgMn single crystals show that in accordance with the sign of the single-site anisotropy $D$, ZnMn is "Ising-like," i.e., the Mn moments lie parallel to the $c$ axis. CdMn is "$X\ensuremath{-}Y$-like" with the easy axis in the basal plane. MgMn is isotropic, "Heisenberg-like." Dominance of spin-orbit scattering leads to a qualitative understanding of the anisotropy.
TL;DR: In this paper, the law of approach to saturation (LAS) was applied to a great variety of ferromagnetic materials and a general correlation between the inhomogeneity parameter A and the anisotropy field HA, of the form HA = An (n ≈ 1.4) was found.
TL;DR: The variation of the magnetic susceptibility of condensed oxygen with temperature and hydrostatic pressure up to 0.6 GPa has been investigated in this paper, yielding an empirical relation between the exchange parameter and the intermolecular distance.
Abstract: The variation of the magnetic susceptibility of condensed oxygen with temperature and hydrostatic pressure up to 0.6 GPa has been investigated. The results yield an empirical relation between the exchange parameter and the intermolecular distance. High-field magnetisation data on alpha -oxygen indicate a spin-flop; the corresponding anisotropy agrees fairly well with results of magnetic dipole calculations which also include a prediction for the direction of the magnetisation axis. Evidence is presented for magnetic long-range order in beta -oxygen.
TL;DR: In this paper, a simple magnetic transition model was proposed for perpendicular recording with a single-pole head, and it was shown that the amplitude of the transitions is proportional to the coercivity H c of the recording medium and is independent of the saturation magnetization M s if M s is gsim (3/4π) H c.
Abstract: A simple magnetic transition model is proposed for perpendicular recording with a single-pole head. It has been found that the amplitude of the transitions is proportional to the coercivity H c of the recording medium and is independent of the saturation magnetization M s if M_{s} \gsim (3/4\pi) H_{c} . Experimental proof using Co-Cr sputtered films is also given.
TL;DR: In this paper, the magnetic ordering in a hexagonal antiferromagnetic system with both the exchange anisotropy energy and the single-ion anisotropic energy was studied by using the molecular field approximation.
Abstract: The magnetic ordering in a hexagonal antiferromagnetic system with both the exchange anisotropy energy and the single-ion anisotropy energy is studied by using the molecular field approximation. It is shown that the magnetic moments in an ordered phase appearing at T ≤ T N form either a collinear structure with the moments parallel or antiparallel to the hexagonal axis or a triangular structure in the basal plane, and that an arrangement of the moments at T ∼0 shows a variety of structures. Thus, the system exhibits a variety of magnetic ordering processes as the temperature lowers. Our results may give a systematic explanation of anomalous ordering processes observed in recent experiments.
TL;DR: In this article, the effects of applied magnetic fields and applied stresses on the domain structures of amorphous ribbons with transverse or oblique magnetic anisotropy were studied.
Abstract: SEM techniques are used to study domain structures in amorphous ribbons with transverse or oblique magnetic anisotropy. Domain widths are much finer than in ribbons with longitudinal anisotropy, and vary with ribbon dimensions and anisotropy constant. The effects of applied magnetic fields and applied stresses are also discussed.
TL;DR: In this article, the formation of the fcc phase in Co-Cr films under conditions otherwise favorable to formation of hcp phase was found to be directly related to partial pressure or throughput of nitrogen in the system as shown using controlled leaks of both pure nitrogen and air.
Abstract: The presence of as little as 2.3×10−5 Pa (1.73×10−7 Torr) of residual nitrogen gas in an rf sputtering chamber has been found to promote the formation of the fcc phase in Co‐Cr films under conditions otherwise favorable to the formation of the hcp phase. The fcc phase follows the disorientation of the hcp phase as the nitrogen partial pressure or throughput increases. The occurrence of the fcc phase is directly related to the partial pressure or throughput of nitrogen in the system as shown using controlled leaks of both pure nitrogen and air. The nitrogen may destroy the columnar microstructure and the film perpendicular magnetic anisotropy which is due to the well‐oriented hcp phase. This sensitivity to nitrogen in the background gases makes it necessary to achieve a low background pressure in the sputtering chamber if films with perpendicular magnetic anisotropy are to be obtained.
TL;DR: In this article, an exchange scattering of spin-polarized electrons from a Fe surface was observed using epitaxial Fe(110) films of less than 80 atomic layers, prepared on a W (110) ribbon.
Abstract: Exchange scattering of spin-polarized electrons from a Fe(110) surface was observed using epitaxial Fe(110) films of less than 80 atomic layers, prepared on a W(110) ribbon. The Fe films could be magnetized along the easy axis (001) by current pulses, using the W ribbon as a strip line. Because stray fields can be neglected for these extremely thin films, they remained in a saturated remanent state in which they were analyzed by electron scattering. As the direction of magnetization coincided with the primary beam polarization, and with the normal of the scattering plane, exchange and spin-orbit-coupling contributions to the scattering asymmetry, respectively, A/sub ex/ and A/sub so/, could be determined separately, by separate reversal of primary beam polarization and magnetization. A maximum value of A/sub ex/ = 34 +- 10% was measured for specular reflection in the (100) plane with an angle of incidence of 31/sup 0/, for electron energies of 46 eV.
TL;DR: Ternary Sm2Co17−xTx systems in which Co is replaced by V, Ti, Zr, and Hf have been studied to ascertain the efficacy of these elements in improving the permanent magnet characteristics of Sm 2Co17-based magnets as discussed by the authors.
Abstract: Ternary Sm2Co17−xTx systems in which Co is replaced by V, Ti, Zr, and Hf have been studied to ascertain the efficacy of these elements in improving the permanent magnet characteristics of Sm2Co17‐based magnets Single phase materials were obtained for 0?x?10 X‐ray diffraction measurements indicate that these compounds exhibit either the hexagonal‐Th2Ni17 or the rhombohedral‐Th2Zn17 structure The lattice parameters are found to increase with x and in the order Hf