Showing papers on "Ferromagnetism published in 1969"
TL;DR: In this article, a comprehensive review of the application of magnetic oxides in the electronics industry is presented, with reference to the theoretical background of such materials existing up to the end of 1967, and the relation of magnetic anisotropy energy and the permeability is discussed in terms of applications to transformers, inductors, etc.
224 citations
TL;DR: In this paper, the shape of the reciprocal magnetic susceptibility vs temperature curves measured between 4.2° and 300°K is of the Stoner type and suggests for these alloys a density-of-states curve varying appreciably in the Fermi region leading to a low effective energy.
Abstract: Measuring the magnetization of various alloys in the Ni3Al and Ni3Ga phases, we found that going to higher Ni concentrations within these phases, a transition from strongly exchange enhanced paramagnetism to weak ferromagnetism takes place at 74.5 and 76 at.% Ni, respectively. The shape of the reciprocal magnetic susceptibility vs temperature curves measured between 4.2° and 300°K is of the Stoner type and suggests for these alloys a density‐of‐states curve varying appreciably in the Fermi region leading to a low effective Fermi energy. This conclusion is confirmed by the strong curvature of the magnetization in high magnetic fields. These results and the fact that an increase of the magnetic field applied on ferro‐magnetic samples effects a large increase of the magnetization even at the lowest temperatures (4.2°K) and in the highest fields (200 kOe) led us to a description in terms of the itinerant electron model. The use of this model seems justified by the fact that in agreement with calculations by Edwards and Wohlfarth, the magnetic data of both paramagnetic and ferromagnetic compositions fit nicely on straight lines in σ2 vs H/σ plots, this being so for all temperatures (down to 4.2°K) and all magnetic fields between 4 and 200 kOe. Combining the magnetic data and low‐temperature specific‐heat data, we obtained some information on the bandshape at the Fermi level. We cannot conclude, however, to more than a nice qualitative agreement with the Stoner model at this moment. As would be expected in highly polarizable metals and alloys, small amounts of Fe dissolved both in paramagnetic and in ferromagnetic alloys in the Ni3Al and Ni3Ga phases lead to giant moment inducement.
203 citations
TL;DR: The magnetic properties of dichalcogenide compounds, CoS 2, CoSe 2, NiS 2, NiSe 2 and the system Co(S x Se 1- x ) 2, were studied by means of magnetic measurement, neutron diffraction and NMR as discussed by the authors.
Abstract: The magnetic properties of dichalcogenide compounds, CoS 2 , CoSe 2 , NiS 2 , NiSe 2 and the system Co(S x Se 1- x ) 2 , were studied by means of magnetic measurement, neutron diffraction and NMR. The exchange interaction J s w of the ferromagnetic CoS 2 ( T c =124°K, θ p =220°K, p eff =1.76µ B , n =0.84µ B and H i =52 kOe) was estimated to be 24 cm -1 per Copair from the analysis of spin wave theory. While, CoSe 2 ( T N =90°K, θ p =-160°K and p eff =1.72µ B ) showed an antiferromagnetic spin ordering with MnSe 2 type. NiS 2 (θ p =-740°K and p eff =2.48µ B ) had no magnetic ordering even at 4.2°K. NiSe 2 exhibited weak constant paramagnetism with metallic conductivity. In Co(S x Se 1- x ) 2 , (0≤ x ≤1), the magnetic properties and the magnetic phase diagram were determined, and this system showed to have “low spin state” with 1µ B per Co. Some discussions were given from the theoretical stand points.
150 citations
TL;DR: Ferromagnetic resonance has been observed in single crystals of the family La1−xPbxMnO3 with 0.45 GHz frequency from 13 to 25 GHz and in the temperature range from 77 to 430 °K as discussed by the authors.
Abstract: Ferromagnetic resonance has been observed in single crystals of the family La1−xPbxMnO3with 0.25 < x < 0.45 from 13 to 25 GHz and in the temperature range from 77 to 430 °K. The line width, ΔH, exh...
147 citations
TL;DR: In this article, the magnetic properties and lattice parameters for 13 compounds of the composition RIn3 (Cu3Au structure) are reported and the magnetic measurements have been performed between 4.2° and 500°K with magnetic fields up to 30 kOe.
Abstract: The magnetic properties and the lattice parameters for 13 compounds of the composition RIn3 (Cu3Au structure) are reported. The magnetic measurements have been performed between 4.2° and 500°K with magnetic fields up to 30 kOe. With the exception of compounds with R=La, Sm, Y, and Yb Curie–Weiss behavior is observed in the high‐temperature region. At low temperatures the magnetic behavior for compounds in which R=Ce, Nd, Sm, Gd, Tb, Dy, Ho, and Er is ascribed to antiferromagnetic ordering. In the case of PrIn3 magnetic ordering is prevented by crystalline fields. The splitting of the J = 4 state of Pr3+ by cubic crystalline fields has been calculated for various combinations of fourth‐ and sixth‐order potentials. Possible energy diagrams are presented.
143 citations
TL;DR: In this article, the low-temperature spontaneous magnetization is inhomogeneously distributed in magnetic polarization clouds of large total moment (over 8 \mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$) extending over many atoms.
Abstract: Neutron scattering experiments reveal that in weakly ferromagnetic Ni-Cu alloys near the critical composition the low-temperature spontaneous magnetization is inhomogeneously distributed in magnetic polarization clouds of large total moment (over ${8\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$) extending over many atoms.
136 citations
TL;DR: In this article, the magnetic moment decreases very sharply from 1.3µ B in 30 at% Ni to 0.2 µ B in 20 at%Ni and the Mossbauer absorption spectra observed at liq. He temperature show the appearance of antiferromagnetism in the low nickel concentration range.
Abstract: Magnetization, Mossbauer absorption spectra and lattice constants have been measured on the γ phase (f.c.c.) Fe-Ni alloys of 20∼30 at% Ni using finely grained samples in which the γ→α martensitic transformation can be suppressed even at liq. He temperature. The magnetic moment decreases very sharply from 1.3µ B in 30 at% Ni to 0.2µ B in 20 at% Ni. The Mossbauer absorption spectra observed at liq. He temperature show the appearance of antiferromagnetism in the low nickel concentration range. These experimental facts indicate that in these composition range the alloys consist magnetically of two phases, namely ferromagnetic and antiferromagnetic ones. This magnetic heterogeneity is caused by the statistical concentration fluctuation and is discussed quantitatively by considering a Gaussian type concentration distribution. The temperature and composition variations of the lattice constant and the thermal expansion coefficient can also be interpreted quantitatively on the basis of the same Gaussian type conce...
112 citations
99 citations
TL;DR: The two groups of metallic compounds Gd3+X3− (X=N, P, As, Sb, Bi) have the rocksalt structure and except for ferromagnetic GdN they are antiferromagnetic as discussed by the authors.
Abstract: The two groups of metallic compounds Gd3+X3− (X=N, P, As, Sb, Bi) and Gd3+Z2− (Z=S, Se, Te) have the rocksalt structure and except for ferromagnetic GdN they are antiferromagnetic. Powder neutron diffraction measurements on GdS, GdSe, GdSb, and GdBi show them to have order of the second kind. The exchange interactions are discussed on the basis of the magnetic structure and susceptibility measurements.
91 citations
TL;DR: In this paper, the free energy expression of Wohlfarth for a very weak itinerant ferromagnet is amended by the addition of volume-dependent terms given by Belov, and the forced magnetostriction and pressure dependence of the Curie temperature are calculated.
Abstract: The free energy expression of Wohlfarth for a very weak itinerant ferromagnet is amended by the addition of volume-dependent terms given by Belov. Hence the forced magnetostriction and pressure dependence of the Curie temperature are calculated. The effects depend on the volume dependence not only of the effective interaction energy but also of the fine details of the band structure. Magnetostriction measurements on ZrZn2 by Ogawa and Waki are used to estimate that here partial differentialTc/partial differentialP = -2·4 degK kbar-1. A variety of results relating to the effect is deduced from elementary thermodynamics. For a very weak itinerant ferromagnet corrections to the result deduced from the Belov equation are obtained. Reference is made to recent measurements by Fawcett et al. on dilute platinum and palladium alloys.
85 citations
TL;DR: In this article, it was found that pure Ni film deposited onto the glass substrate cooled by liquid nitrogen was amorphous and ferromagnetic, and spontaneous magnetization in the amorphized state showed a marked decrease compared with the crystalline state.
TL;DR: In this paper, the thermodynamics of single superparamagnetic particles are studied by means of a Monte Carlo technique which was recently derived for the calculation of compact ferromagnets, and an exact (numerical) calculation of the magnetization and of the internal energy of the particle is obtained.
TL;DR: In this article, the authors measured the temperature dependences of electrical resistivity and thermal expansion for face-centered cubic Fe 65 (Ni 1-x Mn x ) 35 ternary alloys.
Abstract: The temperature dependences of electrical resistivity and thermal expansion were measured for face-centered cubic Fe 65 (Ni 1- x Mn x ) 35 ternary alloys. The electrical resistivity of ferromagnetic alloys ( x 0.3) increases below the Neel temperature and shows a resistance minimum. These behaviors are explained in terms of the magnetic scattering by induced moments below the magnetic ordering temperature. The expansion of volume due to the magnetic ordering was observed in both ferro- and antiferromagnetic alloys. To explain the volume expansion by the magnetic ordering, a new mechanism of magnetovolume effect based on the change of cohesive energy due to the spin polarization in 3 d band is proposed.
TL;DR: Ferric fluoride (FeF3) is a transparent green uniaxial weak ferromagnet with a Curie temperature of 365 °K as mentioned in this paper, which is the only known material which has spontaneous magnetic moment at room temperature.
Abstract: Ferric fluoride (FeF3) is a transparent green uniaxial weak ferromagnet (canted antiferromagnet) with a Curie temperature of 365 °K. FeF3 is far more transparent in the visible and uv than any other known material which has a spontaneous magnetic moment at room temperature. FeF3 at room temperature has 6 absorption bands between 7000 A and the band edge which is at 2440 A. There is a local absorption minimum of α = 4.4 cm−1 in the green at 5225 A. The Faraday rotation is 180 °/cm at 5225 A and increases to 1100 °/cm at 3000 A. The birefringent phase retardation at 5200 A is about 80 000 °/cm. The two indices of refraction are about 1.54 in the visible spectrum.
TL;DR: In this paper, the spin wave eigenfrequencies and eigenfunctions for a model ferromagnetic film, in the presence of both exchange and magnetic dipole interactions, were examined.
Abstract: We have examined the spin-wave eigenfrequencies and eigenfunctions for a model ferromagnetic film, in the presence of both exchange and magnetic dipole interactions A detailed computer study of spin waves in a thirty-layer film is presented for the case where the exchange and dipole interactions are of comparable strength We discuss in detail both surface and "bulk" modes for this case Also, the symmetry properties of the eigenvectors are discussed, along with a method for converting certain two-dimensional dipole sums to a rapidly converging form
TL;DR: In this paper, the variation of the critical temperature (the Curie or Neel temperature) of a magnetic crystal randomly diluted with non-magnetic atoms is evaluated as a function of concentration p of magnetic atoms by the effective Hamiltonian method based on the Ising and the Heisenberg models.
Abstract: The variation of the critical temperature (the Curie or Neel temperature) of a magnetic crystal randomly diluted with non-magnetic atoms is evaluated as a function of concentration p of magnetic atoms by the effective Hamiltonian method based on the Ising and the Heisenberg models. The specific heat of Ising ferromagnet above the Curie temperature is calculated for various concentrations in order to see the existence of Schottky-type maximum. The critical index of susceptibility and the Curie temperature for diluted ferromagnet is also calculated using Pade approximation to check the idea that the lowering of the Curie temperature with the decrease of p is attributed to the decrease of effective dimensionality of ferromagnetic system.
TL;DR: In this paper, the electrical resistivity has been measured between 4.2 and 300°K for RA1 2 compounds, where R denotes the rare-earth elements La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Yb and Y.
TL;DR: In this paper, the anomalous low-temperature (1.4° to 4.2°K) specific heat, the ferromagnetic Curie temperature, and the magnetic moment of Ni-Cu solid solutions were measured near the composition where ferromagnetism terminates.
Abstract: The low‐temperature (1.4° to 4.2°K) specific heat, the ferromagnetic Curie temperature, and the magnetic moment of Ni–Cu solid solutions were measured near the composition where ferromagnetism terminates. The anomaly in the specific heat cannot be accounted for by the bT3 ln T term expected from electron‐paramagnon interaction, but it can be interpreted as a magnetic cluster contribution independent of temperature from 1.4° to 4.2°K. Another magnetic contribution is included in the term of the specific heat linear in temperature. Whether the maximum in the linear term at 50–54 at.% Cu should be attributed to this magnetic contribution or to the (enhanced) electronic specific heat is uncertain. For alloys near the critical composition the Curie temperature, as determined by methods based on high field data, is distinctly higher than that measured at low fields.
TL;DR: The intimate correlation between the mechanisms causing magnetism and superconductivity in uranium compounds has been verified again-in novel systems.
Abstract: The intimate correlation between the mechanisms causing magnetism and superconductivity in uranium compounds has been verified again—in novel systems.
TL;DR: In this article, electrical resistivity, thermoelectric power, and magnetic susceptibility or magnetization have been measured at room temperature and below on compositions surrounding NiAl (49-51 at. % Al) and CoAl (42-54% Al).
TL;DR: In this paper, single crystal octahedra of HgCr2Se4 of up to 1.5mm on an edge were grown by chemical transport in a closed system.
TL;DR: The transition in Fe 2 Ti from ferromagnetism in iron-rich to antiferromagnetic magnetism in titanium-rich material is attributed to excess iron atoms which enter titanium sites.
TL;DR: In this article, it was observed that the increase of flow stress produced by cooling below the Curie temperature can be completely reversed upon heating, and that the formation of martensite is irrelevant.
Abstract: When face-centred cubic alloys with the physical properties typical of Invar are strained over a sufficient range of deformation variables, peculiar deformation characteristics become apparent. For example, there is an unusually large temperature-dependence of the flow stress, completely atypical of f.c.c. metals. Factors such as compositional departure from the Invar range, the intentional formation of martensite, arranged prohibition of martensite, and compositional control of Curie temperatures, were manipulated to determine the origin of the deformation behaviour. Only the Invars reacted as a class, and ferromagnetism appeared causal both to the onset of the special deformation and to its nature. It was observed that the increase of flow stress produced by cooling below the Curie temperature can be completely reversed upon heating, that the formation of martensite is irrelevant, and that the nucleation of martensite is inhibited by the spontaneous ferromagnetism. Observations such as these is...
TL;DR: In this article, the magnetic properties of amorphous iron films were investigated and it was shown that the magnetic moment of the iron atoms is smaller in the amorphized than in the crystalline structure.
Abstract: In a previous paper a method has been described to produce thin films of amorphous iron by simultaneous condensation of iron and small additions of oxygen, silicon, or germanium onto a substrate at 20 °K. During annealing the amorphous films crystallize within a narrow range of temperature. In this paper the magnetic properties of these films are investigated. By a new lowtemperature άgnetometer the magnetization curves can be registered for the different states of annealing. It results that even in the amorphous state iron is ferromagnetic. Below a critical concentration of the oxygen, silicon, or germanium admixtures the magnetic moment of the iron atoms is smaller and the coercive force is greater in the amorphous than in the crystalline structure. Above that concentration the magnetic moments in the two structures are equal, whereas the coercive force of the amorphous films is smaller than that of the crystalline ones. The results are explained by a concentration depending short range order in the amorphous films.
TL;DR: In this article, the spontaneous volume magnetostriction of metallic ferromagnets is discussed based on the band theory and the dependence on lattice parameters of the band width and of the molecular field coefficient are taken into account.
Abstract: The spontaneous volume magnetostriction of metallic ferromagnets is discussed based on the band theory. Dependences on lattice parameter of the band width and of the molecular field coefficient are taken into account. The difference between the lattice parameters in the ferromagnetic and paramagnetic states at 0°K is expressed in terms of the difference between the energies in the ferromagnetic and paramagnetic states. It is understood qualitatively why the absolute value of negative spontaneous volume magnetostriction ( e.g. in Ni) is generally small while that of positive one ( e.g. in Invar) is sometimes large. By assuming a simple but reasonable density of states curve for fcc Fe–Ni alloys the spontaneous volume magnetostriction of the alloys is calculated. The calculated value for Invar alloy is seven times larger than that for Ni metal in absolute value; the agreement with experimental results is satisfying.
TL;DR: The chemical vapor deposition process for growing epitaxial yttrium iron garnet (YIG) has matured to the point where films of varying geometry and thickness from ½ to as great as 40 μ can be readily grown on several orientations of gadolinium gallium garnet, yttium aluminum garnet and YIG itself as mentioned in this paper.
Abstract: The chemical vapor deposition process for growing epitaxial yttrium iron garnet (YIG) has matured to the point where films of varying geometry and thickness from ½ to as great as 40 μ can be readily grown on several orientations of gadolinium gallium garnet, yttrium aluminum garnet, and YIG, itself. As a measure of the quality of the films, line widths (at 9.4 GHz and room temperature) as small as 0.6 and 1.4 Oe were obtained in samples with substrates removed and intact, respectively, without a major effort toward improvement. Magnetostatic modes, exchange modes, and ferromagnetic normal modes having comparable exchange and demagnetization energies were observed in these films and in thin bulk disks and were explained in detail by a new theory which applies not only to films, but also to samples of arbitrary shape and size, and includes the effects of exchange and demagnetization energies. The frequencies of the general normal modes were calculated by casting the linearized equation of motion of the magn...
TL;DR: In this article, the electrical resistance vs. temperature curve of an amorphous Fe80P13C7 alloy has a minimum at low temperature, which varies from specimen to specimen and covers a range from 10° to 50°K.
Abstract: The electrical resistance‐vs‐temperature curve of an amorphous Fe80P13C7 alloy, obtained by rapid quenching from the liquid state, has a minimum at low temperature. Because the quenching conditions cannot be accurately controlled, the temperature at which the minimum occurs varies from specimen to specimen and covers a range from 10° to 50°K. A study of 14 different specimens shows a correlation between this temperature and the ratio of the resistances at helium temperature to that at room temperature. This correlation is interpreted in terms of the existence of regions of short range order, or small amounts of crystalline phases in imperfectly quenched specimens.
TL;DR: In this article, powder patterns of magnetic domains on various crystallographic surfaces of pure and doped hematite single crystals have been studied at room temperature and in the vicinity of the Morin transition.
Abstract: Powder patterns of magnetic domains on various crystallographic surfaces of pure and doped hematite single crystals have been studied at room temperature and in the vicinity of the Morin transition. The observations below room temperature were made with an apparatus employing thermoelectric cooling modules. It was concluded that the domains were either slabs or cylinders of irregular transverse cross section with axes lying parallel to the basal plane. The domain walls were determined to be 180° ones. At the Morin transition, a light diffuse colloidal line is formed at the boundary between two phases, one weakly ferromagnetic and the other antiferromagnetic. On warming or cooling, the boundary sweeps across the crystal in a characteristic fashion.
TL;DR: In this paper, a diffraction of polarized neutrons of a single crystal of the ferromagnetic compound UFe2 at 84°K (T/TC = 0.49) has been made by diffraction analysis of all reflections out to a sinθ/λ value of 0.41 A−1.
Abstract: A study has been made by the diffraction of polarized neutrons of a single crystal of the ferromagnetic compound UFe2 at 84°K (T/TC = 0.49). The flipping ratios of all reflections out to a sinθ/λ value of 0.41 A−1 have been measured. These measurements show that, at this temperature, the Fe atom has a magnetic moment of 0.38 μB and that there is a small but significant moment of the U atom, parallel to the Fe moment, of about 0.03 μB. The spin density distribution at the U atom position is very nearly spherically symmetric, but the spin density at the Fe site is seen to have large deviations from spherical symmetry, being elongated in the direction of the cube edges and contracted along the nearest‐neighbor connecting line. Good agreement between observed and calculated structure factors is obtained by using a shallow form factor of the 5f3 type for the U moment, and by using an Fe form factor calculated on the basis of 65% of the magnetic electrons having Eg symmetry and 35% T2g symmetry.