Showing papers on "Magnetic anisotropy published in 1970"

Interband Effects on Magnetic Susceptibility. : II. Diamagnetism of Bismuth

Abstract: The magnetic susceptibility of conduction electrons in the presence of spin-orbit interaction is calculated. The model is that due to Wolff which assumes two bands separated by a small energy gap. Our calculation shows that due to the interband effect of the magnetic field the susceptibility has a large contribution to diamagnetism when the Fermi energy lies in the band gap region. This result is applied to bismuth, and possible interpretations are proposed for the dependence of its magnetic property on the effective valence number and the cause of the anisotropy.

Paramagnetic Anisotropy, Electronic Structure, and Ferromagnetism in Spin S = 32 Manganese(II) Phthalocyanine

Abstract: Measurements are reported of magnetization and the average magnetic susceptibility of manganese (II) phthalocyanine in the range 1.7–300°K, which confirm that the Mn(II) atom is in an S = 3 / 2 spin state, and that weak ferromagnetic interactions are present in the crystal, presumably between adjacent molecules. Single crystals of MnPc are moderately anisotropic; the principal magnetic moment μ‖ = 4.0 μB remains constant between 80–300°K while μ⊥ increases from 4.4 μB (300°K) to 5.0 μB (90°K). This magnetic anisotropy is consistent with a 4A2g ground state into which the excited term 4Eg is mixed by spin–orbit coupling. Possible pathways for superexchange are considered.

Paramagnetic Anisotropy, Low Temperature Magnetization, and Electronic Structure of Iron(II) Phthalocyanine

Abstract: Magnetic anisotropy, magnetization, and average magnetic susceptibility have been measured for iron (II) phthalocyanine. The anisotropy was measured from the room temperature to about 90°K, the average susceptibility from 296 to 1.57°K, and the magnetization was measured at 1.57°K for field strengths between 1100 and 15 000 Oe. The results are interpreted in terms of a 3B2g ground state with a zero‐field splitting parameter D = 64 cm−1, and g‖ = g⊥ = 2.74. Iron (II) phthalocyanine is an unusual example in which a large magnetic anisotropy arises entirely from the zero‐field splitting. The danger inherent in the existing method of evaluation of ligand‐field parameters from the average magnetic susceptibility data has been highlighted, and the advantages of magnetic anisotropy studies in deducing the ligand‐field parameters and the electronic structures are discussed. A change of about 70° of the “setting angle” between 290 and 90°K is observed in this crystal when measured with b axis vertical. It is shown...

Electron transitions in strong magnetic fields

Abstract: Various types of electron transitions in strong magnetic fields due to qualitative changes of the energy spectrum of electrons (and hence of properties of materials) were predicted and observed at certain critical values of the magnetic field. Metallic and semiconducting Bi-Sb alloys were investigated in the concentration range of Sb up to 8 at % and from 8 at % to 16 at % correspondingly. The transversal and longitudinal magnetoresistance measurements on Bi-Sb alloy single crystals were performed at various orientations of current and fields relative to the crystalline axes. The measurements were performed in magnetic fields up to 600 kOe.at temperatures from 4.2 to 77°K. The following types of electron transitions were discovered: (a) semiconductor-metal transition; (b) a transition from a semiconducting state into a state with an abnormally small energy gap between the zones referred to as a “quasimetallic”; (c) a transition semiconductor-“quasimetal”-semiconductor; (d) a transition semiconductor-“quasimetal”-semiconductor-metal; and (e) metal-semiconductor transition.

Determination of the Spin–Orbit and Trigonal‐Field Splittings of the 5E State of Fe2+ in ZnO, ZnS, CdS, ZnSe, CdSe, ZnTe, and CdTe Crystals by Magnetic Susceptibilities

Abstract: The magnetic susceptibilities of the Fe2+:ZnSe, Fe2+:CdSe, Fe2+:ZnTe, Fe2+:CdTe, Fe2+:ZnS, Fe2+:CdS, and Fe2+:ZnO crystals have been measured over the temperature range of 2–300°K in order to determine the spin–orbit and trigonal‐field (for CdS and ZnO) splittings of the ground orbital state 5E of Fe2+ in the crystal lattice. The first five crystals are magnetically isotropic with no detectable trigonal‐field effects, and their susceptibilities tend toward constant values at very low temperature. From the temperature dependence of the susceptibility, we obtain the spacings of the A1 and T1 component of the 5E group of the first five crystals as 12, 12, 16, 18, and 15 cm−1, respectively. These results give spin–orbit coupling constants | λ | = 85, 81, 96, 99, and 99 cm−1, respectively, when used in conjunction with the optical data of the 5E−5T2 transitions. The Fe2+:CdS crystals show a small magnetic anisotropy but otherwise similar susceptibility data which yield 16 cm−1 for the A1−T1 spacing, 1 cm−1 for...

Analysis of Exchange‐Coupled Magnetic Thin Films

Abstract: Presented in this paper are some new analytical results for two exchange‐coupled magnetic thin films. The formulation of the problem which is used is similar to that of Goto et al., who reduced the determination of the magnetic configuration of the films in the presence of an external magnetic field to the evaluation of elliptic integrals. Derived herein is an expression for the second variation of the magnetic energy, thereby allowing an investigation of the stability of previously determined magnetic configurations. Evaluation of this expression, as well as determination of the magnetic configuration, must be done numerically, and tables giving magnetic configurations and critical fields are included for a variety of thickness combinations and magnetic parameters. In addition, new analytical results are presented for several limiting cases. Transcendental equations have been derived which give the threshold fields for arbitrary film parameters when the easy axes are mutually parallel in the two films and when the external field is either parallel or perpendicular to the common easy axis. Expressions are also developed for the critical fields in composites involving both very thin and very thick films, and the magnetic properties of a pair of very thin films are shown to be simple combinations of the constituents' magnetic properties. Finally, several discrepancies are discussed between the approximate results of Goto et al. and the exact results obtained herein.

Coercivity and wall motion

Abstract: The process of magnetization reversal in ferromagnets with uniaxial crystal anisotropy is discussed. It is shown that the "critical-size concept" has no relevance to coercivity. Critical fields are distinguished as nucleation fields and propagation, or pinning, fields. The pinning of walls is discussed and illustrated by experiments on various substances. Intrinsic pinning in highly anisotropic materials is predicted.

Crystal Fields and the Magnetic Properties of Praseodymium and Neodymium

Abstract: The magnetic properties of Pr and Nd single crystals have been studied by neutron-diffraction and susceptibility measurements. In contrast to earlier results on polycrystals, monocrystalline Pr is found not to be magnetically ordered, because of crystal field effects, but a magnetic field induces a large moment. Anisotropic effective exchange results in a large magnetic anisotropy. The complex magnetic structure of Nd is substantially modified by a magnetic field.

Transition Region in Recorded Magnetization Patterns

Abstract: Various theoretical approaches have been recently offered to describe the writing and demagnetization processes in magnetic recording. All invariably correlate their calculations with readback pulse measurements, thus clouding their results with the dominant readback losses. In this paper a self‐consistent iterative approach was used to calculate the demagnetization in an isolated recorded transition between two areas of opposite magnetization, as a function of the coercivity, remanence, and thickness of the recording medium. Lorentz transmission microscopy was used to verify the predictions of the theoretical calculations. For this purpose, a series of thin magnetic films of different magnetic properties and thicknesses were prepared and then recorded with an inductive‐type transducer. The magnetization transition regions were observed to resemble a sawtooth structure. The walls of the sawtooth were inclined towards the easy magnetization direction, and the magnetization on either side of these walls was...

Magnetic properties of gadolinium ortho-aluminate

Abstract: An account is given of specific heat, magnetic susceptibility and magnetic moment measurements on gadolinium ortho-aluminate, GdAlO$_{3}$, at temperatures in the liquid helium range. This compound orders antiferromagnetically at 3.87 K. In the antiferromagnetic state, its properties can be accounted for satisfactorily as those of an array of S-state magnetic ions with isotropic magnetic properties, coupled together by exchange interaction between nearest neighbours and subject to a 'single ion' anisotropy force due to the crystalline electric field. Because the structure approximates closely to a simple cubic lattice of Gd$^{3+}$ ions, magnetic dipole effects have little influence on the ordering. The exchange and anisotropy forces are calculated from the experimental data, and the measured properties are compared with various theoretical predictions for a simple two sublattice antiferromagnet. The variation of the specific heat in the critical region close to the Neel point is compared with that of other compounds undergoing magnetic transitions at low temperatures, and a consistent pattern of behaviour is found.

Photoinduced Uniaxial Magnetic Anisotropy and Optical Dichroism in Silicon‐Doped Yttrium Iron Garnet [YIG(Si)]

Abstract: Photoinduced magnetic anisotropy and optical dichroism have been studied in silicon‐doped YIG at cryogenic temperatures. These effects belong to a new class of magneto‐optical effects in which the overlap properties of the excited states of ions on different sites are important. The spectral variation of the photoinduced dichroism shows the position of the operative Fe+ + state to be at about 10 000 cm−1. Photoinduced torque studies are interpreted to indicate that a large fraction of the Fe+ + ions may be moved among various sets of inequivalent sites on irradiation by intense white light.

Formation and magnetic properties of ultrafine spinel ferrites

Abstract: Investigations of the formation and magnetic properties of Mn δ Co 1-δ Fe 2 O 4 formed in alkaline aqueous solution by the coprecipitation method are covered. The lattice constant of these ferrites apparently reduced with decreasing average particle size below about 500 A. The coercive force ratio of MnFe 2 O 4 and Co-Fe 2 O 4 is 1 to 50 and equal to that of the crystal magnetic anisotropy coefficient K 1 of sintered ferrites. As the average particle size became larger, the coercive force and the apparent remanence increased linearly, and superparamagnetic critical size was determined. The sizes range, for example, from 50 to 100 A for CoFe 2 O 4 and from 150 to 200 A. for MnFe 2 O 4 . From the correlation between the average particle size and their magnetization, the limit size of ferromagnetic critical particle was also determined. Results obtained in this experiment are approximately in accord with Neel's Version of the theory on thermal fluctuation aftereffect of magnetic fine particles.

Nuclear Magnetic Resonance Study of the Easy Axis of Magnetization in Manganese Bismuthide

Abstract: The zero-field NMR of Mn 55 in ferromagnetic MnBi has been observed in the temperature range 4.2°K to 500°K. Resonance signals from nuclei in the domain and domain wall are separately observed at 225.01 MHz, and 206 MHz, respectively, at 294°K. As the temperature is decreased, the quadrupole splitting and the frequency of the central line for the domain signal decrease gradually below 142°K and a temperature somewhat lower than 142°K, respectively, and change abruptly at 90°K. These results show that below 142°K the magnetic moment deviates gradually from the c -axis and flops into the c -plane at 90°K. The temperature dependence of the NMR intensity has also been observed, from which a qualitative temperature variation of the anisotropy constant K 1 has been obtained. The hyperfine field and e 2 q Q / h extrapolated to 0°K are -224.5 kOe and 14.0 MHz, respectively.

Magnetic‐Susceptibility Anisotropy of CO and CS

Abstract: The asymmetric frequency shifts in the Zeeman splittings of the first rotational lines of CO and CS have been measured. The magnetic anisotropy evaluated from these shifts is ( − 8.2 ± 0.9) × 10−6 for CO and ( − 24 ± 3) × 10−6 for CS, both in ergs/gauss2·mole. The molecular quadrupole moments are estimated from the anisotropies, and the g factor of CS is shown to be negative.

Contribution of Fe2+, Mn3+ and Fe3+ ions to the magnetic anisotropy of MgxMn0.6Fe2.4-xO4

Abstract: The temperature dependences of the saturation magnetization sigma s and of the anisotropy K1 were measured in single crystals of MgxMnyFe3-x-yO4, 0

Anisotropic magnetic susceptibility of rocks under mechanical stresses

Abstract: The magnetic susceptibility of a rock under a uniaxial compression (σ) decreases along the axis of compression and increases along the direction perpendicular to the axis, with an increase of σ. Thus, the magnetic susceptibility of a compressed rock becomes anisotropic.

Instability of an Isolated Straight Magnetic Domain Wall

Abstract: An isolated straight magnetic domain wall along the y axis results when a thin slab of magnetic material in the xy plane is exposed to a nonuniform z axis magnetic field of the form Hz=βx, if β is sufficiently large. The behavior of this magnetic system as β decreases is discussed. A magnetic energy calculation shows that sinusoidal deviations from the straight wall become energetically favorable at a critical value βc. The wavelength of this distortion at βc and βc are both expressed in terms of magnetic material properties. Experimental observations of this instability in YbFeO3 are given, and the magnetic parameters determined this way are in reasonable agreement with those obtained by using other methods. Effects of material inhomogeneieties are discussed, and the transition from the initially distorted straight wall to the demagnetized state of stripe domains is shown.

Effect of Single-Ion Anisotropy on Two-Spin-Wave Bound State in a Heisenberg Ferromagnet

Abstract: We consider the scattering of two spin waves in a uniaxial (easy axis) Heisenberg ferromagnet with single-ion anisotropy. The two-spin-deviation problem is solved exactly at zero temperature. We find (for $Sg\frac{1}{2}$), in addition to the usual two-spin-wave bound states, a new "single-ion bound state," in which at the zone corner the two spin deviations are on the same site. When the magnitude of the anisotropy is comparable to the exchange interaction, the single-ion bound state becomes the dominant feature of the bound-state spectrum. For arbitrary spin there is a critical anisotropy strength above which the single-ion bound state exists throughout the Brillouin zone. We conclude that the presence of single-ion anisotropy enhances the possibility of experimental observation of the bound states.

Utilization of a Rotating Sample Magnetometer

Abstract: The RSM can be used to detect magnetic moment (vM≥5×10−6 emu), rotational hysteresis (vWR/H≥10−2 emu), spin flop (vM≥5×10−5 emu), and properties related to anisotropy energy [vK/H, v(χ⊥−χ∥)H and vMx≥5×10−6 emu], i.e., anisotropy constants, anisotropic susceptibility, and anisotropic spontaneous magnetization. Samples are either symmetric about, or offset from, an axis of rotation which is set parallel or perpendicular to an applied dc field. Coils are oriented to sense magnetization along or normal to the field axis. For measuring specific parameters, a phase sensitive detector, an electronic integrator, or an oscilloscope is employed. Detailed expressions relating magnetic properties and signal output are presented, along with illustrative experimental results.

Magnetic Properties of TbIn3, TbPt3 and HoIn3

Abstract: Neutron‐diffraction measurements made on powder samples of TbIn3, TbPt3, and HoIn3 show that all of these compounds exhibit antiferromagnetism below Neel temperatures of 37 ± 1°K, 20.5 ± 0.5°K, and 11.5 ± 0.5°K, respectively. The magnetic reflections from TbPt3 can be indexed on a doubled chemical cell of cubic symmetry. A possible magnetic model consists of an arrangement where the Tb moments are aligned in opposite directions in adjacent (111) magnetic planes. The magnetic reflections from TbIn3 and HoIn3 can be indexed on a doubled chemical cell of tetragonal symmetry. An appropriate magnetic arrangement is one in which the rare‐earth moments are aligned in opposite directions in adjacent (110) magnetic planes. For TbIn3 the moment direction makes an angle of 10 ± 5° with the unique or c axis of the magnetic cell; for HoIn3 the corresponding moment direction is 58 ± 5°. The saturation ordered moment on the rare‐earth atom sites in all three compounds is approximately 10% less than the calculated or expected values. The magnetic structures are compared with predictions of the indirect exchange theory.

Exchange Anisotropy in Single Crystals of Cu–Mn Alloys

Abstract: Low-temperature magnetic measurements have been carried out on the field-cooled single crystals of Cu-Mn alloys containing 14 to 23 at.% Mn. Torque measurements indicate that the easy direction of induced unidirectional anisotropy (exchange anisotropy) occurs in the direction of the field applied during cooling and that the constant of unidirectional anisotropy ( e.g. , 1.1×10 4 erg/cm 3 for 17.8 at.% Mn) is independent of the crystallographic direction of the field during cooling. The experimental result is interpreted on the basis of the nucleation and growth process of mutually-interacting ferromagnetic and antiferromagnetic domains. It has also been found that a small uniaxial anisotropy is additionally induced. The field-cooled specimen is almost free from the rotational hysteresis, this being in marked contrast to the large rotational hysteresis in the specimen cooled in zero field.

Heteronuclear magnetic double resonance measurement of carbon-13 chemical shifts in NN-dimethylformamide and related compounds

Abstract: A 13C chemical shift difference of 5 p.p.m. between the methyl groups of NN-dimethylformamide has its origin in the electric field of the carbonyl group; this effect may be as important as magnetic anisotropy in determining 1H chemical shifts.

Anisotropy of wall energy in orthoferrites

Abstract: Wall anisotropy causes bubble domains to be elliptical. A formula relating the eccentricity of an elliptical bubble to the anisotropic wall energy is derived, and an experimental technique for measuring the wall anisotropy is described. In Sm 0.55 Tb 0.45 FeO 3 a measured anisotropy energy of 1.7 percent of the wall-energy density at room temperature is responsible for eccentricities as large as 0.4 at average bubble radii equal to 85 percent of the bubble strip-domain transition radius. The relationship between material parameters and wall-energy anisotropy is briefly discussed.

Magnetic Behavior of MnCr2S4 in High Magnetic Fields

Abstract: Magnetization curves obtained by pulsed field techniques in MnCr2S4 at low temperatures display two types of transition. At magnetic fields of the order of a few tens of kilo‐oersteds, a transition from a Neel structure to a Yafet and Kittel one is occurring. At a field of about 105 Oe, another transition takes place between a Yafet and Kittel structure and a collinear one where the magnetic moments of the nonequivalent A sites may be different in length and sign.