Showing papers on "Curie temperature published in 1983"
TL;DR: In this article, the effects of uniaxial drawing or poling on the structural changes involved in the ferroelectric-to-paraelectric phase transition in copolymers of vinylidene fluoride and trifluoroethylene were examined and compared to the behaviour of as-crystallized films.
229 citations
TL;DR: In this paper, a model was proposed to describe the simultaneous changes in topological and chemical short range order during structural relaxation of metallic glasses, and the free volume and order parameter during isothermal and isochronal annealing were calculated.
213 citations
TL;DR: In this paper, the magnetic properties of the cubic NaZn 13 type pseudobinary compounds La(T x Si 1-x ) 13 were studied for T = Fe, Co and Ni in the temperature range 4.2-300 K.
206 citations
Patent•
30 Sep 1983
TL;DR: In this article, an autoregulating, electrically shielded heater employs a laminated structure having two magnetic alloy permeable materials of widely differing Curie point temperatures and preferably of differing resistivities.
Abstract: An autoregulating, electrically shielded heater employs a laminated structure having two magnetic alloy permeable materials of widely differing Curie point temperatures and preferably of differing resistivities. A constant current supply is connected across the laminate such that current flows in the laminae along parallel paths. Due to skin effect, the current is confined to a thin region of a first lamina which is located between the other lamina and the electrical return path. This first lamina has the lower Curie temperature and preferably the higher resistivity of the two laminae to produce heating proportional to I 2 R 1 . When the Curie temperature of the first lamina is approached, the current spreads into the other lamina which may have a lower resistivity and higher Curie temperature and heating is obtained by I 2 R 2 where I 2 is a constant due to the constant current source and preferably R 2
196 citations
TL;DR: In this paper, the authors performed self-consistent KKR CPA calculations for the disordered local moment (DLM) state of Fe, Co, Ni and Cr at different temperatures.
Abstract: The authors perform self-consistent KKR CPA calculations for the disordered local moment (DLM) state of Fe, Co, Ni and Cr at different temperatures. The DLM state is a model for the metals above their Curie temperatures, in the paramagnetic state. They find the dependence of the local magnetic moment on temperature and determine the Stoner temperature. For Fe, they obtain the magnitude of the local moment above the Curie temperature to be about 85% of the ground-state value, whereas for Co and Ni it is about 50% of the ground-state value. For Cr they find that no self-consistent local magnetic moment exists in this DLM state. With slightly increased lattice spacing the sizes of the local moments are found to increase for both Fe and Ni.
162 citations
TL;DR: In this paper, the electronic structure of paramagnetic iron is calculated self-consistently within the local spin density functional formalism by applying the coherent potential approximation with the muffin-tin potential model.
Abstract: The electronic structure of paramagnetic iron is calculated self-consistently within the local spin density functional formalism by applying the coherent potential approximation with the muffin-tin potential model. The effective exchange parameters Jn are calculated as the interaction energy between two magnetic moments in the paramagnetic medium obtained. A discussion on the magnetism of iron above the Curie temperature is presented using the Heisenberg model with the calculated Jn.
147 citations
TL;DR: An intercalated 2H-type layer compound, Cr 1/3 NbS 2, was investigated by magnetic and neutron diffraction measurements as mentioned in this paper, and it was found that this compound is a helimagnet with a very long period along the c-axis and with the spins in the c -plane.
Abstract: An intercalated 2H-type layer compound, Cr 1/3 NbS 2 , was investigated by magnetic and neutron diffraction measurements. It was found that this compound is a helimagnet with a very long period along the c -axis and with the spins in the c -plane. The magnetic behavior is similar to that of an easy-plane type ferromagnet except for the magnetization curve in the c -plane. The Curie temperature is 127 K. The saturation magnetization corresponds to 2.9 µ B /Cr. The uniaxial anisotropy constant, K 1 , is -1.46×10 6 ergs/cc at 4.2 K. The magnetizatiom curve in the c -plane shows a metamagnetic behavior, the critical field of which is as low as 1.5 kOe except near T c . Small angle scattering measurements showed a helical structure with Q =0.013 A -1 (480 A period). The helical spin structure and the metamagnetism is explained as due to the antisymmetric exchange interaction.
143 citations
TL;DR: In this paper, the formation and magnetic properties of Heusler compounds of the general formula X 2 YSn were studied, where X represents a 3D transition metal or Cu and where Y represents a second 3d transition metal of group IV A, VA and VI A of the periodic table.
104 citations
TL;DR: In this article, the properties of hot-pressed lanthanum-modified PbTiO/sub 3/ ceramics were measured as a function of crystal tetragonality.
Abstract: Dielectric, electromechanical, optical, and mechanical properties of hot-pressed lanthanum-modified PbTiO/sub 3/ ceramics were measured as a function of crystal tetragonality, c/a, in a range of tetragonal-to-cubic phases. The results obtained in this study are summarized as follows: The c/a changes linearly as a function of lanthanum content. Similarly, Curie point changed linearly and remanent polarization, coercive field, and coupling factors decreased with decreasing c/a. The sample with c/a = 1,010 showed the maximum transmittance of 61% wavelengths above 600 nm. The internal stress measured using the microindentation technique decreased with decreasing c/a in the tetragonal region and was zero in the cubic region.
98 citations
TL;DR: In this article, the authors carried out elastic and inelastic neutron scattering experiments on a MnSi single crystal with the use of a neutron polarized-beam technique, and observed a characteristic polarization dependence in the magnetic Bragg reflections of the spiral phase, as well as the spin-wave excitations and the critical scattering near ${T}_{c}$.
Abstract: MnSi is a cubic ferromagnet with a long-wavelength spiral below its Curie temperature at 29 K. Recent theoretical and experimental studies have shown that this spiral is only right handed because of the lack of a center of symmetry in the Mn atomic arrangement. We have carried out elastic and inelastic neutron scattering experiments on a MnSi single crystal with the use of a neutron polarized-beam technique. A characteristic polarization dependence was observed in the magnetic Bragg reflections of the spiral phase, as well as the spin-wave excitations and the critical scattering near ${T}_{c}$. This polarization dependence persists into the ferromagnetic phase under a magnetic field and also at temperatures as high as 150 K.
97 citations
Patent•
29 Mar 1983
TL;DR: In this article, the authors proposed a method to obtain a photomagnetic recording medium having large coercive force and a large angle of Kerr rotation and requiring a small quantity of recording energy by forming a thin film of an amorphous alloy represented by formula I or II on a substrate so that the film has an axis of easy magnetization in a direction perpendicular to the surface of a magnetic film.
Abstract: PURPOSE:To obtain a photomagnetic recording medium having large coercive force and a large angle of Kerr rotation and requiring a small quantity of recording energy by forming a thin film of an amorphous alloy contg a heavy rare earth element and a light rare earth element on a substrate so that the film has an axis of easy magnetization in a direction perpendicular to the surface of a magnetic film CONSTITUTION:A thin film of an amorphous alloy represented by formula I or II(where R is a light rare earth element such as La, Ce, Pr, Nd, Pm, Sm or Eu, each of A and B is a heavy rare earth element such as Gd, Tb or Dy, A and B are different from each other, 015<=x<=035, 000
TL;DR: In this paper, the results of Ozima & Sakamoto as a decomposition process were compared with those of Readman & O'Reilly with some exceptions, which may have been caused by the differences in starting materials.
Abstract: Summary. Low-temperature oxidation of titanomagnetites (x = 0.3, 0.5 and 0.7) was investigated in this study. Starting materials were carefully prepared so that their Curie points and lattice constants were in agreement with reliable values. Changes in Curie points and lattice constants during the process of low-temperature oxidation were then studied in detail. Independent heatings were performed under various conditions and oxidation parameters (z) were determined by chemjcal analyses. Though this method could not provide continuous z values like the weight increase method, reproducibility was very high when samples were heated in the same condition and the various states were consistent with each other. Oxidation states from z = 0.0 to 1.0 were realized in three compositions. When titanomagnetite in basalt was heated under various conditions a change occurred, either oxidation, decomposition or reduction. Natural titanomagnetite minerals closely followed the oxidation-reduction trends established for synthetic samples. The present results are consistent with those of Readman & O’Reilly with some exceptions. The differences may have been caused by the differences in starting materials. The results of Keefer & Shive are similar to those of Ozima & Sakamoto and are completely different from ours. They detected a rhombohedral phase and indicated that the decomposition process proceeds in the same manner reported by Ozima & Sakamoto. We are unable to account for their results. It may be useful to consider the results of Ozima & Sakamoto as a decomposition process. This idea has not been presented previously in the literature.
Journal Article•
TL;DR: In this paper, un comportement de verre de spin est suggere par les anomalies observees dans la variation thermique de l'aimantation mesuree dans un champ de 0,5 kOe.
Abstract: Mesures d'aimantation et de spectres Mossbauer entre 4,2 et 300 K. Les recents modeles developpes pour ce systeme n'expliquent pas la decroissance rapide de l'aimantation et de la temperature de Curie au voisinage de x=2. Un comportement de verre de spin est suggere par les anomalies observees dans la variation thermique de l'aimantation mesuree dans un champ de 0,5 kOe
TL;DR: In this paper, the interaction of magnetic (Tc) an first-order distortion-type structural (TD) transitions in the CoxNi1−xMnGe system was investigated using an ac susceptibility method under hydrostatic pressure up to 1.3 GPa.
TL;DR: A phase transition at a temperature immediately below the melting point of poly(vinylidene fluoride) form I has been found by means of differential scanning calorimetry (d.s.c.) and infra-red (i.r.) vibrational spectroscopy as mentioned in this paper.
TL;DR: In this paper, the temperature, microstructural and environmental variations of the fracture properties of ferroelectric ceramics are surveyed, showing that fracture toughness decreases on heating through the Curie temperature.
Abstract: This paper surveys the temperature, microstructural and environmental variations of the fracture properties of ferroelectric ceramics. Earlier work shows that fracture toughness decreases on heating through the Curie temperature. There is also anomalous behavior in the strength at small crack sizes, indicative of a grain size effect. Further, the strength properties are known to be adversely affected by the presence of water in the atmosphere. Data from recent indentation studies on barium titanate are used to investigate these phenomena.
TL;DR: A series of random copolymers of vinylidene fluoride and trifluoroethylene containing 52, 65, 73, and 78 mol % VF2 has been shown by X-ray and dielectric techniques to undergo Curie transi...
Abstract: A series of random copolymers of vinylidene fluoride and trifluoroethylene containing 52, 65, 73, and 78 mol % VF2 has been shown by X-ray and dielectric techniques to undergo Curie transi...
TL;DR: In this paper, a model based on the idea of localized magnetic moments is presented which allows to calculate the local magnetic moment expectation values of FeNi alloys, and the model allows the iron magnetic moments to orient parallel or antiparallel to the magnetization axis, depending on the local environment.
Abstract: A model based on the idea of localized magnetic moments is presented which allows to calculate the local magnetic moment expectation values of FeNi alloys. The only parameters of the model are the exchange integralsJ
FeFe,J
FeNi,J
NiNi. By assuming a “mixed” exchange interaction the concentration dependence of the exchange integralsJ
FeFe andJ
FeNi is calculated. The model allows the iron magnetic moments to orient parallel or antiparallel to the magnetization axis, depending on the local environment. It explains the magnetic abnormalies of FeNi Invar alloys as for example the concentration dependence of the mean magnetic moment and the Curie temperatures as well as the characteristic “flat” courves of the spontaneous magnetization.
01 Dec 1983
TL;DR: In this paper, an active magnetic regenerator is described along with the method of calculation and the temperature profiles for a normal regenerator and a magnetic regenerative refrigerator are shown, and the theory of these devices is predicted by solving the partial differential equations that describe fluid and the magnetic solid.
Abstract: The adiabatic temperature change with field which is limited to about 2 K/Tesla for ferromagnets near their Curie temperatures by the change of magnetization with temperature and the lattice heat capacity is discussed. Practical magnetic refrigerators operate on a regenerative cycle such as the Brayton cycle. This cycle can be executed through the use of an active magnetic regenerator, i.e., a regenerator composed of magnetic material that is cycled in an out of a magnetic field with appropriate fluid flows. The theory of these devices is predicted by solving the partial differential equations that describe fluid and the magnetic solid. The active magnetic regenerator is described along with the method of calculation. Temperature profiles for a normal regenerator and a magnetic regenerative refrigerator are shown.
TL;DR: In this article, the PTCR properties of porous semiconducting barium titanate ceramics with Curie points from 60° to 360°C were investigated, and the magnitude of the effect of the Curie point on the effect was found to decrease self-on-with increasing Curie Point within this temperature range.
Abstract: PTCR characteristics in porous semiconducting barium titanate ceramics with Curie points from 60° to 360°C were investigated. The magnitude of the PTCR effect in these cerumics decreases self-onsistently with increasing Curie point within this temperature range. A PTCR efSect of more than 4 orders of magnitude was ahserved, for a Ba0.44Pb0.6TiO3 ceramic with a Curie point of 360°C.
TL;DR: In this article, Li 1− x M 2+ x 2 □ x 2 ) TaO 3 with M=Zn, Ni, Mg and Ca was found to be stable even at x=05, where 25% of the Li sites are vacant.
TL;DR: In this paper, the electrical conductivity σ of polycrystalline Ni-Zn ferrites of various compositions was investigated from room temperature to the neighbourhood of the Curie temperature.
Abstract: The electrical conductivity σ of polycrystalline NiZn ferrites of various compositions was investigated from room temperature to the neighbourhood of the Curie temperature. The electrical conduction in these ferrites is explained on the basis of the hopping mechanism. Plots of log(σT) versus 103/T are almost linear and show a transition near the Curie temperature. The activation energy in the ferrimagnetic region is in general less than that in the paramagnetic region.
TL;DR: In this paper, the spectral distribution of magnetic fluctuation scattering from metallic nickel has been studied above the Curie temperature with unpolarized and polarized neutrons, and it was shown that the main part of the magnetic scattering above T/sub c/ does not come from the spin-wave ridge in (..omega.., q) space but from a spectral part centered at zero energy with a broad energy distribution.
Abstract: The spectral distribution of the magnetic fluctuation scattering from metallic nickel has been studied above the Curie temperature with unpolarized and polarized neutrons. The present measurements confirm previous results of a spin-wave-like mode above T/sub c/. It is shown, however, that the main part of the magnetic scattering above T/sub c/ does not come from the spin-wave ridge in (..omega.. , q) space but from a spectral part centered at zero energy with a broad energy distribution.
TL;DR: In this article, the depolarization behavior of ordered and disordered lead scandium-tantalate (PST) ceramics has been studied by Byer-Roundy and Chynoweth method.
Abstract: The depolarization behavior of ordered and disordered lead scandium-tantalate (PST) ceramics has been studied by Byer-Roundy and Chynoweth method. A sharp decrease of the spontaneous polarization takes place in a narrow temperature range very close to the Curie temperature Tc for the ordered PST materials. For the disordered PST materials, however, the depolarization takes place within a wide temperature range much lower than the temperature of maximum dielectric constant Tm. Evidence of microdomain activities has been observed in disordered materials. The reversible pyroelectric effect is discussed in terms of the micro-macro transition of the domains in disordered PST materials.
TL;DR: The magnetic properties of melt-spun iron-zirconium alloys are drastically altered by the addition of hydrogen as discussed by the authors, which increases both the Curie temperature and the moment per iron atom, from 252K and 1.6 mu B, respectively, to 382K and 2.0 mu B.
Abstract: The magnetic properties of melt-spun iron-zirconium alloys are drastically altered by the addition of hydrogen. The transformation of the magnetic order in Fe89Zr11 from collinear ferromagnetism to asperomagnetism below 60 K is suppressed in Fe89Zr11H20, which remains ferromagnetic at all temperatures. Hydrogenation increases both the Curie temperature and the moment per iron atom, from 252K and 1.6 mu B, respectively, to 382K and 2.0 mu B.
TL;DR: The temperature dependence of dielectric permittivities, shear moduli and internal friction of LiCSO4 crystals were measured in this paper, where large anomalies were found in G1 and G2 shear models and in internal friction Q-1 for the samples in a and b directions.
Abstract: The temperature dependence of dielectric permittivities, shear moduli and internal friction of LiCsSO4 crystals were measured Large anomalies were found in G1 and G2 shear moduli and in the internal friction Q-1 for the samples in a and b directions, near the Curie point Tc = 202 K The temperature dependence of stress-strain hysteresis loops was also studied In the samples cut out along the a direction a single loop was found while in the b direction a double hysteresis loop was observed
TL;DR: In this article, a quantitative discussion is given of recent paramagnetic diffuse neutron scattering data on bcc Fe above T c, and it is concluded that the data are inconsistent with the giant short-range order hypothesis of Prange and Korenman, Capellmann and Sokoloff.
TL;DR: In this paper, the coupling between magnetism and chemical short-range order (SRO) was investigated in ferromagnetic alloys through an experimental investigation of the temperature dependence of the local order in both the Ferromagnetic and paramagnetic phases around the Curie temperature.
Abstract: The coupling between magnetism and chemical short-range order (SRO) is investigated in ferromagnetic alloys through an experimental investigation of the temperature dependence of the local order in both ferromagnetic and paramagnetic phases around the Curie temperature. Experiments were carried out in quenched dilute FeCo alloys through zero-field NMR at 59Co nuclei. The conditions which allow the equilibrium SRO parameters to be obtained and their temperature variation to be measured from low-temperature NMR spectra are carefully discussed. An abrupt change in the behaviour of the local order is observed at the Curie temperature. The authors use a very simple theoretical model based on an Ising-Heisenberg Hamiltonian to account qualitatively for the experimental results. They point out the importance of the magnetic coupling on the chemical SRO so that measurement of local order in equilibrium states allows only a combination of chemical and magnetic pair interactions to be determined.
TL;DR: In this paper, the effect of pressure on the critical phenomena of the itinerant-electron ferromagnet UFe 2 around the Curie temperature has been discussed regarding three current topics in the study of itinerantelectron magnetism: • -high-magnetic-field experiments on the strongly exchange-enhanced paramagnetic materials Pd, YCo 2, UAl 2 and UCo 2; • -itinerant-electric magnetism in 5f metals: the Laves phase compounds UM 2 (M = Fe, Co, Ni, Al,
TL;DR: In this article, the effect of degenerate multi-bands with t2g and eg symmetry on the Curie temperature, the magnetisation curve, the amplitude of local moments and the susceptibility of iron was investigated using the detailed density of states generated by the recursion method for the tight binding model.
Abstract: A previously developed theory of itinerant-electron magnetism at finite temperatures is generalised to include the effect of degenerate multi-bands with t2g and eg symmetry by adopting the static functional integral method and the coherent potential approximation (CPA). Numerical calculations of the Curie temperature, the magnetisation curve, the amplitude of local moments and the susceptibility are made for iron by using the detailed density of states generated by the recursion method for the tight-binding model. Calculated results are shown to account for finite-temperature properties of iron. In particular, the calculation explains the observed very weak temperature dependence in the spin-density asphericity, which cannot be explained by the Stoner theory. The authors' results are compared with those obtained by alternative approaches in which the five sub-bands are taken to be equivalent.