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Showing papers on "Ferromagnetism published in 1970"


Journal ArticleDOI
TL;DR: In this article, the properties of perovskite-type oxide LaMnO 3 were studied experimentally and theoretically using a phenomenological approach or the Spin-Hamiltonian formalism.
Abstract: Magnetic properties of the perovskite-type oxide LaMnO 3 were studied in detail, experimentally and theoretically. The properly stoichiometric LaMnO 3 had a weak ferromagnetic moment in addition to the antiferromagnetic character with a Neel temperature of 141°K. It was found to be a parasitic weak ferromagnet. These results can be successfully explained using a phenomenological approach or the Spin-Hamiltonian formalism. The theoretical results show that the antiferromagnetic spin axis should be along the b -axis of the orthorhombic crystal axes and the ferromagnetic moment along the c -axis. The relation between a layer-type ( A -type) antiferromagnetic superexchange interaction and the Jahn-Teller distortion of Mn 3+ ions is also discussed.

217 citations


Journal ArticleDOI
TL;DR: In this article, the crystal and magnetic structures have been investigated by neutron diffraction in Mn285Ga115 and the high temperature quenched DO19 phase has a triangular antiferromagnetic structure with magnetic moments.

203 citations


Journal ArticleDOI
TL;DR: In this paper, the Curie temperatures and saturation moments at 4.2°K and 1000°K have been obtained for cubic Laves phase compounds RFe2 (R=Gd, Tb, Dy, Ho, Er, and Y) and RxY1−xFe2.
Abstract: Magnetic measurements in fields up to 30 kOe and for temperatures between 4.2° and 1000°K have been performed for cubic Laves phase compounds RFe2 (R=Gd, Tb, Dy, Ho, Er, and Y) and RxY1−xFe2 (R=Gd, Tb, and Er). The Curie temperatures and saturation moments at 4.2°K are given. A compensation in the temperature dependence of the magnetization is only observed for the various compounds in a certain range of x values. Conditions for the occurrence of a compensation point are derived. For the compounds RxY1−xFe2 the iron moment remains constant for 0≤x≤0.8. Above x=0.8 the iron moment increases strongly. The variation of the Fe moments with x is discussed in terms of a nonlocalized moment associated with the iron ions. The moments shown by Er and Tb in ErFe2 and TbFe2 are both 8.3 μB. For most of the compounds RFe2 the lattice constants are given.

154 citations


Journal ArticleDOI
TL;DR: In this article, a detailed discussion of pair correlations ω2(r) = 〈σ 0σr〉 between spins at lattice sites 0 and r on the axes of anisotropic triangular lattices is given.
Abstract: A detailed discussion of pair correlations ω2(r) = 〈σ0σr〉 between spins at lattice sites 0 and r on the axes of anisotropic triangular lattices is given. The asymptotic behavior of ω2(r) for large spin separation is obtained for ferromagnetic and antiferromagnetic lattices. The axial pair correlation for the ferromagnetic triangular lattice has the same qualitative behavior as that for the ferromagnetic rectangular lattice: There is long‐range order below the Curie point TC and short‐range order above. It is shown that correlations on the anisotropic antiferromagnetic triangular lattice must be given separate treatment in three different temperature ranges. Below the Neel point TN (antiferromagnetic critical point), the completely anisotropic lattice exhibits antiferromagnetic long‐range order along the two lattice axes with the strongest interactions. Spins along the third axis with the weakest interaction are ordered ferromagnetically. Between TN and a uniquely located temperature TD, there is antiferro...

139 citations


Journal ArticleDOI
TL;DR: The only known crystals which have spontaneous ferromagnetic moment at room temperature and are transparent well into the visible spectrum are ferric borate, FeBO3, and ferric fluoride, FeF3 as mentioned in this paper.
Abstract: The only known crystals which have a spontaneous ferromagnetic moment at room temperature and are transparent well into the visible spectrum are ferric borate, FeBO3, and ferric fluoride, FeF3. Each of these rhombohedral materials is a canted antiferromagnet with a small moment lying in the plane perpendicular to its unique axis. The Curie temperatures are 348° and 363°K and the room‐temperature moments are 115 and 40 G, respectively. Both materials contain ferric ions in a slightly distorted octahedral environment. Both are green with a series of absorption bands in the visible, a fundamental absorption edge in the violet (FeBO3) or ultraviolet (FeF3), and a large Faraday rotation per unit absorption at room temperature, as high as 14°/dB at 5250 A for FeBO3 and 16°/dB at 4050 A for FeF3. Recent measurements of the magnetic, optical, magneto‐optical, and microwave resonance properties of these materials are discussed. Potential applications of room temperature transparent ferromagnets include microwave magneto‐optical modulation of visible lasers with very low modulation power per unit bandwidth, optical deflection and isolation, magneto‐optic displays, and holograms. Each of these applications is discussed along with the limitations imposed by the optical absorption and birefringence of the available materials. Birefringence interferes with the Faraday effect in most noncubic crystals. Methods for minimizing this interference are described. Finally, requirements for useful transparent ferromagnets are defined and guidelines for finding new materials are suggested.

119 citations


Journal ArticleDOI
TL;DR: By comparing measured and calculated versions of the generalized magnetic response function of nickel over a wide range of temperatures, it is shown that the much-discussed simple model of an itinerant-electron ferromagnet based on a random-phase approximation treatment of the Hubbard Hamiltonian accounts, in its essentials, for the magnetism of that substance as mentioned in this paper.
Abstract: By comparing measured and calculated versions of the generalized magnetic response function of nickel over a wide range of temperatures it is shown that the much-discussed simple model of an itinerant-electron ferromagnet based on a random-phase-approximation treatment of the Hubbard Hamiltonian accounts, in its essentials, for the magnetism of that substance. Thermal neutron inelastic scattering techniques were used to explore the whole Brillouin zone of wave vectors K in nickel up to energies ▄ω of some 2k B T C over the range of temperatures up to 2T C; the computations were based on direct evaluation of the Lindhard expression for the generalized susceptibility, using a tight-binding band structure, followed by exchange enhancement of the spin part as per Izuyama, Kim and Kubo. The contribution to the neutron scattering from orbital motion of the electrons was estimated to be small, and in a special experimental investigation a satisfactorily low upper limit on this quantity for our present p...

119 citations


Journal ArticleDOI
TL;DR: In this article, the effects of exchange on the magnetostatic surface and bulk spin waves of a ferromagnetic film in the regime where the dipole and exchange fields are both important are determined from the solutions of a sixth-order differential equation.
Abstract: The effects of exchange on the magnetostatic surface and bulk spin waves of a ferromagnetic film in the regime where the dipole and exchange fields are both important are determined from the solutions of a sixth‐order differential equation. The eigenstates are admixtures of bulk and surface waves. With an applied magnetic field parallel to the film surface and for small values of the wave vector parallel to the surface, k, the Damon and Eshbach surface state is split into segments which join adjacent bulk branches. No sharp cutoff of the surface branch occurs as the angle between k and the applied field is increased, instead the character of the branch changes continuously from surface‐like to bulk‐like. For values of | k |≳104 a number of branches have significant surface character so that no single branch can be identified with the Damon‐Eshbach surface state. When the applied field is perpendicular to the surface a new type of surface spin wave occurs below the bulk manifold and is characterized by a c...

112 citations


Journal ArticleDOI
TL;DR: In this article, the average magnetic susceptibility of manganese phthalocyanine in the range 1.7-300°K was reported, which confirmed that the Mn(II) atom is in an S 1/3/2 spin state, and that weak ferromagnetic interactions are present in the crystal.
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.

112 citations


Journal ArticleDOI
TL;DR: In this article, the magnetic behavior of compounds of the type TxNbS2 with x = 1 3 and X = 1 4 was studied below room temperature and no magnetic order was found with T = Ti and V.

103 citations


Journal ArticleDOI
TL;DR: In this paper, a functional integral method is proposed to transform the interacting electron system into an average over a system of noninteracting electrons moving in a Gaussian-weighted external magnetic field which acts only on the electronic spins.
Abstract: The understanding of ferromagnets, like iron, which exhibit localized moment behavior above the Curie point yet show itinerancy has long stood as a major theoretical problem. An account will be given of recent progress on this problem which was achieved through functional integral methods. This technique transforms the interacting electron system into an average over a system of noninteracting electrons moving in a Gaussian‐weighted external ``magnetic'' field which acts only on the electronic spins. For a single magnetic impurity in a free electron metal, a single approximation allows one to go from Pauli paramagnetism to localized moment behavior in a smooth manner as the atomic exchange interaction is increased. The two impurity problem leads to an effective exchange coupling as in the Heisenberg model, which is antiferromagnetic for the nondegenerate orbital case studied here. Application of the technique to homogeneous systems leads to damped spin waves in the ferromagnet in lowest approximation.

86 citations


Journal ArticleDOI
TL;DR: In this paper, a four sublattice model is developed which indicates the importance of the excess entropy of the ferromagnetic over the antiferromagnetic phase in exciting the antifromagnetic-ferromagnetic transition, and it is found that application of the theory of exchange inversion to the results leads to serious numerical discrepancies.
Abstract: The critical field required to induce this transition in Fe-Rh alloys close to the equiatomic composition has been measured using pulsed magnetic fields up to 280 kOe. Measurements of the thermal expansion and high field magnetization have also been carried out. It is found that application of Kittel's theory of exchange inversion to the results leads to serious numerical discrepancies. A four sublattice model is developed which indicates the importance of the excess entropy of the ferromagnetic over the antiferromagnetic phase in exciting the antiferromagnetic-ferromagnetic transition. The exchange iteration β between iron sublattices is small and negative and, although its lattice parameter dependence is large and positive, there is no suggestion of exchange inversion corresponding to a change in sign of β at the antiferromagnetic-ferromagnetic transition. Thus the ferromagnetic state is stabilized by the excess entropy even in the presence of antiferromagnetic interactions and this stability is maintained right up to the Curie temperature

Journal ArticleDOI
TL;DR: In this article, electron spin polarization in photoemission from nickel was observed and the preferential direction of the magnetic moment is parallel to the magnetization even for electrons excited from energy states near the Fermi level.
Abstract: We observe electron spin polarization in photoemission from nickel, undetected in earlier experimental investigations. The saturation electron spin polarization for films prepared on hot substrates is higher than for films on cold substrates and the preferential direction of the magnetic moment is parallel to the magnetization even for electrons excited from energy states near the Fermi level.

Journal ArticleDOI
TL;DR: In this paper, the effect of dynamic pinning on epitaxial films of Permalloy, symmetrically coupled with two nickel layers of various thicknesses, was investigated and a reproducible value of the interface energy which is one-tenth of that of the bulk exchange energy was provided.
Abstract: In a first part, we estimate the effect of dynamic pinning [C. F. Kooi, E. P. Wigen, M. R. Shanabarger, and J. V. Kerrigan, J. Appl. Phys. 35, 791 (1964)] due to two ferromagnetic layers upon the spin‐waves resonances in a sandwiched film having a higher magnetization, assuming the interface interaction energy to be of an exchange type. Experiments performed on epitaxial films of Permalloy, symmetrically coupled with two nickel layers of various thicknesses, exhibit results in excellent agreement with theory and provide a reproducible value of the interface energy which is one‐tenth of that of the bulk exchange energy.

Journal ArticleDOI
TL;DR: In this paper, the authors show evidence of long-range magnetic polarization of the palladium matrix in dilute ferromagnetic Pd(Ni) alloys, for alloys containing up to 4.7 at.% nickel.
Abstract: Neutron-scattering experiments show evidence of long-range magnetic polarization of the palladium matrix in dilute ferromagnetic Pd(Ni) alloys. The measured cross sections, for alloys containing up to 4.7 at.% nickel, are interpreted in terms of a model in which the concentration of ferromagnetically aligned giant moments is less than the concentration of nickel atoms.

Journal ArticleDOI
TL;DR: In this paper, the properties of the alloys with the stoichiometric compositions PtMnSn and PtSb are investigated and it is shown that the former has a structure of the CaF 2 (Cl) type while the latter an ordered structure of MgAgAs (Cl b ) type.
Abstract: Crystal structures and magnetic properties of Pt-Mn-Sn and Pt-Mn-Sb alloys have been investigated by means of X-ray analysis, magnetic analysis and nuclear magnetic resonance. It is found that the alloys with the stoichiometric compositions PtMnSn and PtMnSb are ferromagnetic and that the former has a structure of the CaF 2 (Cl) type while the latter an ordered structure of the MgAgAs (Cl b ) type. Pt 1.01 Mn 0.99 Sn 1.00 and Pt 1.01 Mn 1.00 Sn 1.00 alloys have lattice parameters of 6.263 and 6.201 A at room temperature, ferromagnetic Curie temperatures of 360° and 582°K, numbers of Bohr magnetons of 3.65 and 4.14 µ B /mol at 0°K and the internal magnetic field of 204.5 and 220.2 kOe at Mn 55 nucleus at 77°K, respectively.

Journal ArticleDOI
TL;DR: In this paper, the Curie temperature of CuCr 2 X 4 was obtained from the result of measurement of the variation with pressure in the self inductance of search coil wound on the specimen vessel.
Abstract: The pressure coefficient of the Curie temperature of CuCr 2 X 4 was obtained from the result of measurement of the variation with pressure in the self inductance of search coil wounded on the specimen vessel. The coefficients, d T c /d p , were founded to be -11.3×10 -4 °Kkg -1 cm 2 for CuCr 2 S 4 , -4.1×10 -4 °Kkg -1 cm 2 for CuCr 2 Se 4 and nearly zero for CuCr 2 Te 4 , respectively. If the main exchange interaction in a pair of Cr ions is thought to be the ferromagnetic superexchange of the Cr-X-Cr type and the antiferromagnetic direct interaction of the Cr-Cr type, it can be seen from the results of the present experiment that the direct Cr-Cr interaction is more sensitive to lattice compression than the superexchange Cr-X-Cr. The magnetic properties of those compounds are also reported.

Journal ArticleDOI
Saburo Mori1
TL;DR: In this article, various barium orthoferrates over wide Fe 4+ concentrations were prepared and their magnetic properties were investigated, and the triclinic I and rhombohedral phases were shown to have a magnetic structure of one-dimensional antiferromagnet.
Abstract: Various barium orthoferrates over wide Fe 4+ concentrations were prepared and their magnetic properties were investigated. The hexagonal phase with large Fe 4+ concentration is ferromagnetic above the anomaly point. With increasing Fe 3+ , it tends to be antiferromagnetic. The cubictetragonal phases are paramagnetic with positive paramagnetic Curie temperature. In these phases, the Fe 4+ -Fe 4 interaction is ferromagnetic, but the Fe 3+ -Fe 4+ and Fe 3+ -Fe 3+ interactions are antiferromagnetic. Some of the Fe 3+ and Fe 4+ ions in these phases take low spin states due to strong uniaxial crystalline fields caused by neighbouring oxygen vacancies. The triclinic I phase seems to have a magnetic structure of one-dimensional antiferromagnet. The magnetic structures of the triclinic II and rhombohedral phases resemble that of the triclinic I.

Journal ArticleDOI
TL;DR: In this paper, the magnon energies at high symmetry points on the Brillouin zone surfaces in YCrO3 were estimated using the optically observed sidebands of the R lines.
Abstract: From the magnetic susceptibility measurement on YCrO3 above TN=141°K, two exchange constants J1 and J2 are estimated to be J1=−8.7 cm−1 and J2=−1.0 cm−1. In DyCrO3 weak ferromagnetism is observed along the a axis, with TN=146°K. When temperature goes below 5°K, the direction begins to rotate towards the b axis. In SmCrO3 a spin reorientation is found. The direction of weak ferromagnetism changes from the c axis to the a axis when the temperature is lowered below the reorientation temperature Tr=35≈40°K. The magnitude of the weak ferromagnetic moment of Cr3+ decreases rapidly below Tr. Using the values of J1 and J2, we estimate the magnon energies at high‐symmetry points on the Brillouin zone surfaces in YCrO3. By comparing these magnon energies with the optically observed sidebands of the R lines, one may assign the sidebands to the combined excitations of one exciton and one magnon, and of one exciton and two magnons. The observed temperature dependence of these sidebands supports this assignment. The ze...

Journal ArticleDOI
TL;DR: In this paper, it was shown that the powder data cannot indicate an unambiguous magnetic structure, but the magnitude of the ordered moment can be fixed The rms moments associated with ordering of the first and second kinds are 10 and 060 µ� B per nickel atom, respectively, and the total moment is 117 µ� B per Nickel atom.
Abstract: The transition metal dichalcogenides exhibit a wide variety of both electrical and magnetic properties, from insulators to superconductors and from ferromagnetism through antiferromagnetism to diamagnetism NiS 2 is a semiconductor with an anomalous paramagnetic behavior which leaves in doubt the existence of a local moment Previous neutron diffraction data have failed to show any ordering down to 42°K Our neutron powder diffraction data on stoichiometric NiS 2 show a transition at 40°K to a structure which can be described as ordering of the first kind This is followed by an abrupt transition at 30°K in which additional diffraction peaks appear and these are consistent with ordering of the second kind Despite the fact that the powder data cannot indicate an unambiguous magnetic structure, the magnitude of the ordered moment can be fixed The rms moments associated with ordering of the first and second kinds are 10 and 060 µ B per nickel atom, respectively, and the total moment is 117 µ B per nickel atom

Journal ArticleDOI
TL;DR: The 23.8-keV Mossbauer resonance of 119Sn and susceptibility measurements have been used to study the structural and magnetic properties of CeSn3, PrSn3 and NdSn3 intermetallic compounds.
Abstract: The 23.8‐keV Mossbauer resonance of 119Sn and susceptibility measurements have been used to study the structural and magnetic properties of CeSn3, PrSn3, and NdSn3 intermetallic compounds between 293° and 1.6°K. The deterioration of the powder samples, which yields free tin and has led to inconsistent results in the past, is clearly demonstrated in these spectra. Both PrSn3 and NdSn3 exhibit magnetic hyperfine (hf) spectra below their Neel temperatures of 8.6° and 4.7°K, respectively. In PrSn3 one‐third of the Sn nuclei experience a transferred hf field of 67 kOe with the spin direction parallel to the principal electric‐field‐gradient axis while the remaining Sn nuclei display no magnetic splitting. This is interpreted as the result of antiferromagnetic ordering of the first kind. In NdSn3 the magnetic ordering appears to be more complex. In CeSn3 neither magnetic ordering nor the ``incipient ferromagnetism'' previously suggested is seen. The size of the quadrupole interaction and the isomer shift are ne...

Journal ArticleDOI
TL;DR: In this article, the magnetic moment of several ferromagnetic face-centered-cubic iron-nickel alloys in the invar region has been investigated at low temperatures, as a function of both the magnetic field and the temperature.
Abstract: The magnetic moment of several ferromagnetic face-centered-cubic iron–nickel alloys in the invar region have been investigated at low temperatures, as a function of both the magnetic field and the temperature. A vibrating-sample magnetometer was used, for which relative changes in the moment of 3 parts in 105 could be resolved. Such resolution has permitted a detailed analysis of the temperature dependence of ΔM/M, the relative deviation of the magnetic moment from its value at 0 K, in terms of a contribution arising from spin-wave excitations, varying as T3/2, and one from single-particle excitations, varying as T2, both of these at constant volume, together with a term describing the effect of volume dilation on the moment. The fits to the data for H = 10 kOe yield, for 34 at. % Ni:and for 40 at. %Ni:

Journal ArticleDOI
TL;DR: The magnetic properties of amorphous FexPd80−xSi20 alloys (x=0.5−7) obtained by rapid quenching from the liquid state are studied between 1.5° and 300°K and in fields up to 8.40 kOe as mentioned in this paper.
Abstract: Magnetic properties of amorphous FexPd80−xSi20 alloys (x=0.5–7) obtained by rapid quenching from the liquid state are studied between 1.5° and 300°K and in fields up to 8.40 kOe. The amorphous alloys are paramagnetic above the characteristic temperature Td. The observed magnetic moments can be explained by postulating a simple magnetic domain consisting of one Fe atom and its Pd nearest neighbors. This is consistent with the magnetic moments assigned to each Fe atom (μFe=3.0μB) and to each Pd atom (μPd=0.20μB). Below Td superparamagnetic clusters exist in the amorphous alloys. Ferromagnetism is found in amorphous Fe7Pd73Si20 alloys with a Curie temperature of 28°K. Evidence is discussed which demonstrates that the d‐d spin exchange interaction is weaker in the amorphous alloys than in the corresponding crystalline alloys.

Journal ArticleDOI
H. Zijlstra1
TL;DR: In this paper, the process of magnetization reversal in ferromagnets with uniaxial crystal anisotropy is discussed and it is shown that the "critical-size concept" has no relevance to coercivity.
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.

01 Jan 1970
TL;DR: In this paper, the first series of magnetic measurements on small, hydrothermally grown single crystals (1 to 10 mg) were reported, which show that Tb(OH)3, Dy(OH), and Ho(OH)-3 order ferromagnetically at 3.72°, 3.50°, and 2.55°K, respectively.
Abstract: The rare‐earth hydroxides, R(OH)3 with R–La to Yb and Y form a series of simple magnetic crystals isostructural with the hexagonal rare‐earth trichlorides. Compared with most ionic rare‐earth crystals they have relatively small lattice parameters, and one may therefore expect magnetic cooperative effects at readily accessible temperatures. In this paper we report the first series of magnetic measurements on small, hydrothermally grown single crystals (1 to 10 mg) which show that Tb(OH)3, Dy(OH)3, and Ho(OH)3 order ferromagnetically at 3.72°, 3.50°, and 2.55°K, respectively, while Nd(OH)3 and Gd(OH)3 undergo more complex antiferromagnetic transitions near 1.7° and 2.0°K. Er(OH)3 remains paramagnetic down to 1.2°K. Magnetization measurements on Tb(OH)3, Dy(OH)3, and Ho(OH)3 in fields up to 14 kG give saturation moments (corrected for Van Vleck temperature‐independent paramagnetism) of 1350 emu/cc (9.0 μB/ion), 1418 emu/cc (9.6 μB/ion), and 1121 emu/cc (7.6 μB/ion) parallel to the c axis and almost zero perp...

Journal ArticleDOI
TL;DR: Magnetic ordering and superconductivity have been investigated in the system Sn0.97•xMnxTe for 0.16 over the temperature range 0.02≤T≤300°K.
Abstract: Magnetic ordering and superconductivity have been investigated in the system Sn0.97‐xMnxTe for 0.00001≤x≤0.16 over the temperature range 0.02≤T≤300°K. Reciprocal Hall coefficient, 1/Re, for all these samples was ∼1021 cm−3. Samples with x>0.005 showed ferromagnetic ordering with the Curie temperatures varying linearly with x. For 0.0001

Journal ArticleDOI
TL;DR: In this paper, the problem of electron correlation in the ferromagnetism of transition metals is investigated by taking an approximate model Hamiltonian which takes into account the hybridization of the $s$ and $d$ bands.
Abstract: The problem of electron correlation in the ferromagnetism of transition metals is investigated by taking an approximate model Hamiltonian which takes into account the hybridization of the $s$ and $d$ bands. The Green's-function technique is used to obtain the self-consistent ferromagnetic solutions within the Hartree-Fock approximation. An approximate solution of the correlation problem is obtained. The ferromagnetic solutions for which the correlation effects are taken into account are compared with those in the Hartree-Fock approximation. The model is used to investigate the role of the $s\ensuremath{-}d$ interaction in metal-nonmetal transitions. It is also possible to understand the difficulty of observing pressure-induced nonmetal-metal transition.

Journal ArticleDOI
01 Oct 1970
TL;DR: In this paper, measurements of the Raman effect on single crystal ferromagnetic CdCr2Se4 and CcCr2S4 as a function of temperature were reported.
Abstract: Measurements are reported of the Raman effect on single crystal ferromagnetic CdCr2Se4 and CdCr2S4 as a function of temperature. The lines observed at 158 cm−1, 172 cm−1 and 241 cm−1 for CdCr2Se4 and 257 cm−1, 281 cm−1 and 396 cm−1 for CdCr2S4 have been identified as due toГ12+,Г25+ andГ1+ phonons, respectively. Certain lines ofГ1+ orГ25+ symmetry, observed in both materials, show a temperature dependence of the intensity which resembles the behaviour of the spin correlation function. Some of these lines also exhibit a symmetry change at the Curie point. A group theoretical analysis of the eigenvectors of the Raman active modes is given. The results are interpreted in terms of a model proposed by Baltensperger which involves the ion position dependence of the magnetic exchange interaction in order to couple spin system and phonons. The weak frequency shift of the lines, which occurs predominantly in the ordered state, is interpreted in terms of the same model.

Journal ArticleDOI
TL;DR: In this article, 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.
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.

Journal ArticleDOI
TL;DR: A series of solid solutions with the general formula La1−xCaxFe1− xMnxO3, where x is from 0.0 to 1.0, have been synthesized and their structural, magnetic and electrical properties have been studied as mentioned in this paper.
Abstract: A series of solid solutions with the general formula La1−xCaxFe1− xMnxO3, where x is from 0.0 to 1.0, have been synthesized and their structural, magnetic and electrical properties have been studied. Polycrystalline samples were prepared by the usual ceramic method, firing at 1350° under a flow of oxygen gas to keep the cations in the desired valence states. X‐ray diffraction shows these samples to be orthorhombically distorted perovskites for compositions up to x=0.3 and apparently cubic perovskites from 0.3

Journal ArticleDOI
TL;DR: In this paper, a new type of metamagnetism has been found in this paramagnetic state at x = 0.86 and the metamagnetic properties have been measured under a strong magnetic field up to 75 kOe and in the temperature range 4.2°K to 800°K.
Abstract: The magnetic phase diagram of Co(S x Se 1- x ) 2 , the solid solution between ferromagnetic CoS 2 and antiferromagnetic CoSe 2 , has been given by neutron diffraction experiment, where the paramagnetism at absolute zero was found in the range 0.5< x <0.88. This paramagnetic state is named “exchange-compensated paramagnetism”. A new type metamagnetism has been found in this paramagnetic state at x =0.86. This behavior had been already predicted theoretically by M. Hattori, K. Adachi and H. Nakano in J. Phys. Soc. Japan 26 (1969) 642. The metamagnetic properties have been measured under a strong magnetic field up to 75 kOe and in the temperature range 4.2°K to 800°K. The metamagnetism shows the hysteresis without remanence below 34°K and the saturation moment agrees with that of CoS 2 . The obtained results have been analyzed from the thermostatistical standpoint with an analogy of the condensation of imperfect gas and the critical indices have been determined. The origin of the exchange-compensated paramag...