Showing papers on "Ferromagnetism published in 1986"
TL;DR: In this article, a theory for dispersion characteristics of spin waves in ferromagnetic films taking into account both the dipole-dipole and the exchange interactions is developed.
Abstract: A theory is developed for dispersion characteristics of spin waves in ferromagnetic films taking into account both the dipole-dipole and the exchange interactions. An arbitrary orientation of the internal bias magnetic field is assumed. The general case of mixing exchange boundary conditions (surface spin pinning conditions) is considered. The simple analytical dispersion equations are obtained using the classical perturbation theory. The modification of the spin wave spectrum due to surface anisotropy (or pinning conditions) is discussed.
824 citations
TL;DR: It is found that magnetic moments can change discontinuously with volume and that there are ranges of coexistence for different magnetic phases.
Abstract: The different magnetic phases of the bcc and fcc forms of Fe, Co, and Ni are studied by analyzing total-energy surfaces in moment-volume parameter space obtained from energy-band calculations using a local-spin-density approximation. The surfaces, found by calculating total energies while holding both the magnetic moment and the volume fixed, offer a method for studying phases that are inaccessible to traditional self-consistent-field methods. We find that magnetic moments can change discontinuously with volume and that there are ranges of coexistence for different magnetic phases. In the multiphase ranges, these elemental magnetic systems exhibit metamagnetic behavior. Our results show that bcc Co is ferromagnetic for all volumes studied, that fcc Co can exist in either a nonmagnetic or a ferromagnetic phase, and that there is a range of volumes where the two phases can coexist. For Fe, the bcc form exhibits a stable ferromagnetic phase for all volumes considered, but the fcc form can exist in any of three phases---a nonmagnetic, a low-spin, and a high-spin phase---all of which can coexist in limited volume ranges. For Ni, the fcc form exhibits a stable ferromagnetic phase, but the bcc form can exist in both a nonmagnetic and, at expanded volumes, a ferromagnetic phase. The volume ranges for all magnetic phases are clearly identified for the bcc and fcc forms of Fe, Co, and Ni.
509 citations
TL;DR: The temperature dependence of the (single-ion) random anisotropy strength can provide a plausible explanation for certain classes of reentrant phenomena and susceptibility cusps observed in magnetization studies.
Abstract: We summarize and extend our study (using real-space response and correlation functions) of the properties of a continuous-symmetry ferromagnet with random anisotropy, distinguishing between the cases of weak and strong random anisotropy. For the weak-anisotropy case we find three different magnetic regimes, according to the strength of the external magnetic field H. In zero H, the net magnetization is zero, although the ferromagnetic correlation length (FCL) is large. We call a ferromagnet in this first regime a correlated spin glass (CSG). It has a very large magnetic susceptibility, and hence a relatively small coherent anisotropy converts it into a nearly typical ferromagnetic domain structure. Also, a relatively small magnetic field nearly aligns the CSG, producing the second regime, which we call a ferromagnet with wandering axis (FWA). The FWA is a slightly noncollinear structure in which the tipping of the magnetization with respect to the field varies over the system. The tipping angle is correlated over a (field-dependent) correlation length which is smaller than the FCL of the CSG. As the field increases the correlation length in the FWA decreases, until the third regime is reached, wherein the tipping angles (which are smaller than in the FWA) are completely uncorrelated from site to site. We obtain the magnetization or susceptibility (as appropriate) for each of these three regimes. We also show that the temperature dependence of the (single-ion) random anisotropy strength can provide a plausible explanation for certain classes of reentrant phenomena and susceptibility cusps observed in magnetization studies. Neutron scattering studies appear to be consistent with the predicted ${H}^{\mathrm{\ensuremath{-}}1/2}$ dependence of the FCL in the FWA regime, and display the expected rise of the FCL in the CSG regime as the random anisotropy strength decreases with increasing temperature.
359 citations
TL;DR: In this paper, the spin anisotropy of ferromagnetic monolayers of Fe, Ni, and V was calculated and it was shown that the easy direction of magnetization is perpendicular to the plane of the monolayer for Fe and V, but in the plane for Ni.
Abstract: We calculate the spin anisotropy of ferromagnetic monolayers of Fe, Ni, and V. We find that the easy direction of magnetization is perpendicular to the plane of the monolayer for Fe and V, but in the plane for Ni. The result for Fe explains why spin splitting but no spin polarization is observed in recent photoemission experiments on Fe overlayers.
315 citations
TL;DR: In this paper, the basic properties of rare-earth compounds of the type R 2 Fe 14 B, R 2 Co 14 B and several related intermetallic compounds are discussed in terms of magnetic exchange interaction and crystal field theory.
207 citations
TL;DR: In this article, the authors present theoretical studies of basic magnetic response characteristics of superlattice structures formed from alternating layers of ferromagnetic and antiferromagnetic materials, each described through use of a localized spin model.
Abstract: We present theoretical studies of basic magnetic response characteristics of superlattice structures formed from alternating layers of ferromagnetic and antiferromagnetic materials, each described through use of a localized spin model. The geometry explored here is one in which the antiferromagnet consists of sheets parallel to each interface within which the spins are aligned ferromagnetically. The study of the classical (mean-field) ground state as a function of magnetic field shows that a sequence of spin-reorientation transitions occur, particularly for superlattices within which the antiferromagnetic constituent consists of an even number of layers. For the various phases, we present calculations of the spin-wave spectrum, and also the infrared absorption spectrum.
184 citations
TL;DR: The origin of the Curie-Weiss law of the magnetic susceptibility universally observed in ferromagnetic materials is discussed from a point of view that the local spin fluctuation amplitude is almost conserved as discussed by the authors.
Abstract: The origin of the Curie-Weiss law of the magnetic susceptibility universally observed in ferromagnetic materials is discussed from a point of view that the local spin fluctuation amplitude is almost conserved. A fully consistent treatment is presented which can deal with both the ordered phase and the paramagnetic phase on an equal footing. In the case of weakly ferromagnetic limit, Rhodes-Wohlfarth plot is revised from a new stand point. In the ordered phase, observed systematic trends of magnetization curves are explained in connection with the nature of dynamical spin fluctuation spectra. Some new interesting relations among various magnetic data are derived and compared with experiments. Temperature dependence of magnetic susceptibilities of Fe and Ni is also discussed.
176 citations
TL;DR: In this paper, the authors discussed how various types of substitutions can modify the PtMnSb band structure and lead to possible enhancement of the Magneto Optical Kerr Effect (MOKE).
164 citations
TL;DR: Using a first-principles disordered-local-moment picture of itinerant-electron magnetism, the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state is calculated.
Abstract: Using a first-principles disordered-local-moment picture of itinerant-electron magnetism, we calculated the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state.
147 citations
IBM1
TL;DR: In this paper, the transition from nonmagnetic to magnetic behavior in transition-metal ferromagnets is studied by analysis of all possible volume evolutions of the variation of the total energy with magnetic moment.
Abstract: The transition from nonmagnetic to magnetic behavior in transition-metal ferromagnets is studied by analysis of all possible volume evolutions of the variation of the total energy with magnetic moment. In contrast to a large body of previous work, magnetic transitions are shown to be necessarily singular, and usually multivalued and discontinuous. Self-consistent spin-polarized energy-band calculations for bcc nickel, fcc cobalt, bcc vanadium, and fcc iron are presented as examples supporting and illustrating the general conclusions.
135 citations
TL;DR: In this article, a self-consistent all-electron local-spin density-functional studies of the electronic and magnetic properties of a seven-layer Cr(001) film are reported using a full-potential linearized augmented-plane-wave method.
Abstract: Results of self-consistent all-electron local- (spin-) density-functional studies of the electronic and magnetic properties of a seven-layer Cr(001) film are reported using our full-potential linearized augmented-plane-wave method. In agreement with earlier theoretical studies and recent photoemission experiments, a ferromagnetic Cr(001) surface is confirmed but with an associated surface magnetic moment of 2.49${\ensuremath{\mu}}_{B}$. The origin of the surface ferromagnetism is related to the sharp surface density-of-states peak near the Fermi level for the paramagnetic state. The calculated work function for the ferromagnetic state is found to be 4.05 eV---some 0.4 eV lower than that for the paramagnetic state; the difference indicates the importance of the magnetic order on this electrostatic quantity. In agreement with photoemission experiments, we find a prominent majority-spin surface state with a binding energy of 1 eV at the \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} point. Layer-by-layer contact hyperfine fields are evaluated: The core contributions are proportional to the magnetic moment of the corresponding atom, and the conduction-electron contribution shows a Friedel oscillation near the center layer. The contact hyperfine field for the surface atoms is also enhanced in magnitude, and a value of -73 kG is predicted.
TL;DR: In this paper, a mean-field model for amorphous ferromagnetic materials with potential applications in thermomagnetic recording/magneto-optical readout systems is developed.
Abstract: A mean-field model is developed for amorphous ferromagnetic materials with potential applications in thermomagnetic recording/magneto-optical readout systems. The emphasis is on the reduction of the number of adjustable parameters, so that important variables and their effects on magnetic properties can be investigated. The available experimental data on GdCo-, GdFe-, and TbFe-based alloys is compared with the model predictions and good agreement is obtained in all cases. Expressions for the exchange stiffness coefficient and macroscopic anisotropy energy constant are derived and the latter is compared with available experimental data. The results have been used to study domain wall characteristics of the three material systems.
TL;DR: The pyrochlore-structure material Y2Mo2O7 is apparently a well-ordered crystalline compound with a concentrated magnetic, Mo4+, sublattice.
TL;DR: In this article, magnetic and specific heat studies performed on some equiatomic compounds of the series U TX with a special emphasis on non-ferromagnetic UNiAl, UCoAl, URuA1 and URuGa are presented.
Abstract: Results are presented of magnetic and specific-heat studies performed on some equiatomic compounds of the series U TX with a special emphasis on non-ferromagnetic UNiAl, UCoAl, URuA1 and URuGa. The occurrence of magnetism in these compounds is attributed mainly to the 5f electrons of uranium. The systematics of the ground-state properties across the series is discussed with respect to delocalization mechanisms of the 5f electrons. The possible role of spin fluctuations in the low-temperature behaviour of UCoAl, URuAl and URuGa is indicated by magnetic measurements. The compound with the highest γ value, UNiAl (γ = 167 mJ/mol K 2 ), behaves as an itinerant antiferromagnet.
TL;DR: The magnetocrystalline anisotropy of MnAl and MnAlC alloys, in the range of existence of the ferromagnetic τ phase, has been studied by using the singular point detection technique as mentioned in this paper.
Abstract: The magnetocrystalline anisotropy of MnAl and MnAlC alloys, in the range of existence of the ferromagnetic τ phase, has been studied by using the singular point detection technique. The anisotropy field value at 293 K varies from 39 kOe for low manganese and high carbon content to 55 kOe for high manganese and carbon‐free samples. The anisotropy of the MnAl τ phase is well described by using only the K1 anisotropy constant. The temperature dependence of the calculated anisotropy constant indicates that a single ion mechanism is the origin of the magnetocrystalline anisotropy in these alloys.
TL;DR: The reaction of Dy2O3 or Tb4O7 with Nd15Fe77B8 powder during the sintering increases the coercivity of the sintered magnets as discussed by the authors.
Abstract: The reaction of Dy2O3 or Tb4O7 with Nd15Fe77B8 powder during the sintering increases the coercivity of the sintered magnets. These oxides are reduced to metal during the sintering process, resulting in magnets with properties similar to those prepared from the Nd13.5Dy1.5Fe77B8 alloy.
TL;DR: In this paper, the superconducting properties of V/Fe superlatitices showing the interplay between ferromagnetism and superconductivity were investigated. But the results were limited to a few atomic planes.
Abstract: Measurements are reported on the superconducting properties of V/Fe superlatitices showing the interplay between ferromagnetism and superconductivity. When the V layer thickness is on the order of the BCS coherence length and the Fe layer is only a few atomic planes thick, a 2D–3D crossover is observed in the temperature dependence of the parallel upper critical field Hc2‖. This implies the coexistence of superconductivity and ferromagnetism in the Fe layers. Three-dimensional behavior for thinner Fe layers is observed (∼1 atomic plane) and 2D behavior for thicker Fe layers (>10 atomic planes).
TL;DR: The temperature dependence of the AC susceptibility Fe-rich Fe-Zr amorphous alloys having mictomagnetic or spin-glass-like behaviour has been measured in a superposed DC field as discussed by the authors.
Abstract: The temperature dependence of the AC susceptibility Fe-rich Fe-Zr amorphous alloys having mictomagnetic or spin-glasslike behaviour has been measured in a superposed DC field. The Fe-Zr amorphous alloys containing more than 8.6 at.% Zr clearly show sharp peaks at the Curie temperature TC and the spin cluster freezing temperature Tsf. These two temperatures seem to coincide at a critical concentration for the Fe-7.6 at.% Zr alloy, which is considered to be the percolation limit for the long-range ferromagnetic interactions.
TL;DR: It is found that a different sequence of magnetic-field-induced spin-reorientation transitions occur for various values of the interface exchange constant, which affects the spin-wave spectrum and the infrared absorption spectrum of the superlattice structure.
Abstract: We present theoretical studies of the properties of superlattices constructed by alternating films of ferromagnetic and antiferromagnetic materials, each described through use of a localized spin model. The interface between the ferromagnetic and antiferromagnetic constituents is a (110) surface of a bcc lattice. For this system, this geometry places mixed-spin antiferromagnetic sheets adjacent to the ferromagnetic films. The study of the classical ground state as a function of external magnetic field shows that in zero field the ground state has spins canted to minimize total exchange energy at the interface. We find that a different sequence of magnetic-field-induced spin-reorientation transitions occur for various values of the interface exchange constant. For the various phases, we present calculations of the spin-wave spectrum and the infrared absorption spectrum of the superlattice structure.
TL;DR: In this paper, the authors studied the loop shift and contraction properties of ferromagnetic FeNi-antiferromagnetic (FeMn) bilayers and showed that the loop shifts are related to the properties of a disordered interface layer, similar to a spin glass.
TL;DR: The range of fields over which the Arott-plot criterion for ferromagnetism plots are applicable shrinks dramatically as the width of the exchange distribution increases and the spin-glass regime is approached.
Abstract: We have investigated the predictions of a mean-field effective-field model for ferromagnets with a distribution of exchange coupling strengths, concerning the region of validity of the Arott-plot criterion for ferromagnetism. We find that the range of fields over which such plots are applicable shrinks dramatically as the width of the exchange distribution increases and the spin-glass regime is approached.
TL;DR: In this article, the one-electron Schrodinger equation for a noncollinear magnet with arbitrary direction of atomic spin in the magnetic unit cell (MUC) is presented.
Abstract: The one-electron Schrodinger equation for a noncollinear magnet (NCM) with arbitrary direction of atomic spin in the magnetic unit cell (MUC) is presented. By analogy with the usual KKR method the secular equation for an NCM is deduced. The symmetry of the problem is discussed on the basis of spin space groups. It is shown that the symmetry consideration often leads to the secular equation factorising anywhere in the Brillouin zone. The calculation of the electron spectrum of the spin spiral for BCC Fe has been carried out and the calculated energy of the spin wave is in good agreement with the experimental value.
TL;DR: In this paper, the magnetic properties of an orthorhombic intermetallic compound Mn 11 Ge 8, which was formerly referred to as Mn 3 Ge 2, has been investigated on a single crystal specimen at temperatures between 80 K and 800 K.
Abstract: Magnetic properties of an orthorhombic intermetallic compound Mn 11 Ge 8 , which was formerly referred to as Mn 3 Ge 2 , has been investigated on a single crystal specimen at temperatures between 80 K and 800 K. The compound has features of a non-collinear antiferromagnet below T t = 150 K, and makes a spin-flopping transition when magnetized along the c axis. It becomes ferromagnetic with a first order transition at T t with the direction of easy magnetization lying along b axis up to its Curie temperature 274 K. The susceptibility follows the Curie-Weiss law above 550 K, with asymptotic Curie temperature 329 K and effective Bohr magneton number per Mn P eff = 3.26.
TL;DR: In this paper, it was shown that in ferromagnetic crystals with uniaxial symmetry the critical field for domain nucleation can be strongly determined by the second anisotropy constant K 2.
TL;DR: In this article, a review is given of recent quantitative analyses, based on realistic electronic structures and magnetic fluctuation spectra, of the effect of spin fluctuations on the magnetic equation of state and on the heat capacity in weak itinerant ferromagnets.
TL;DR: The ferromagnetic state is the most stable for all three phases of Co metal as a function of volume and total-energy local-spin-density energy-band calculations are employed.
Abstract: Total-energy local-spin-density energy-band calculations are employed to study the different structural phases (hcp, fcc, and bcc) and magnetic states of Co metal as a function of volume. In the paramagnetic state, the fcc phase is lowest in energy with magnetic order stabilizing the hcp phase as the (observed) ground state. Unlike the case of Mn, Cr, and Fe which have stable antiferromagnetic states in the fcc phase, the ferromagnetic state is the most stable for all three phases of Co.
TL;DR: In this article, the magnetic and crystallographic properties of intermetallic compounds of the type Ni1-xFexMnSb were determined using standard X-ray diffraction techniques, magnetic measurements and 57Fe Mossbauer spectroscopy.
TL;DR: Mesures des variations de l'aimantation de 3 He adsorbe sur Grafoil, mettant en evidence l'existence d'un effet ferromagnetique de surface.
Abstract: The magnetization of $^{3}\mathrm{He}$ adsorbed on Grafoil has been measured as a function of coverage (two to three layers) at millikelvin temperatures. The observation of a well-defined peak substantially above the free-spin (Curie) value proves unambiguously the existence of a surface ferromagnetic effect.