Showing papers on "Curie temperature published in 1980"
TL;DR: In this paper, it was shown that the degree of order in the B site Sc3+, Ta5+ cations can be controlled by suitable thermal annealing.
Abstract: In Pb(Sc0.5Ta0.5)O3 it has been shown that the degree of order in the B‐site Sc3+, Ta5+ cations can be controlled by suitable thermal annealing. For samples which have been well‐ordered by long annealing, dielectric measurements on single crystals show a normal first‐order ferroelectric phase change at 13 °C and a maximum low‐temperature spontaneous polarization of 23.0 μc/cm2. With increasing disorder, the crystals begin to exhibit the classical diffuse phase transition of a ferroelectric relaxor, with a broad Curie range and strong low‐frequency dielectric dispersion in the transition range. X‐ray diffraction measurements of the size of the ordered microregions suggest that ordering proceeds by different mechanisms in single‐crystal versus ceramic samples, though the resulting effects upon the dielectric behavior are very similar.
769 citations
TL;DR: In this paper, X-ray powder diffraction is used to identify the strong superlattice reflections associated with the ordering of scandium and tantalum ions in the B-site, and to demonstrate quantitatively how the degree of ordering can be modified by suitable thermal treatment.
Abstract: Simple crystal-chemical arguments were used to suggest that in the ferroelectric perovskite lead-scanium-tantalate (PbSc0.5Ta0.5O3) the B-site cations in this simple ABO3 structure should be close to the boundary between order and disorder. Both polycrystal ceramic and single crystal materials of this composition have been grown. In this study X-ray powder diffraction is used to identify the strong superlattice reflections associated with the ordering of scandium and tantalum ions in the B-site, and to demonstrate quantitatively how the degree of ordering can be modified by suitable thermal treatment. Thermal changes associated with the ferroelectric Curie temperature have been measured by differential scanning calorimetry and show very clearly the manner in which the diffuse (broadened) transition in this crystal is sharpened by increase in the B-cation ordering.
410 citations
TL;DR: In this paper, the effect of grain orientation on the dielectric properties of hot-forged ferroelectric Bi4Ti3O12 ceramics has been investigated and the properties are compared with ordinarily fired ones.
Abstract: The effect of grain orientation on the dielectric properties of hot-forged ferroelectric Bi4Ti3O12 ceramics has been investigated and the properties are compared with ordinarily fired ones. The degree of grain orientation f calculated from X-ray diffraction patterns is found to be as large as 0.95. The temperature dependences of the dielectric constant es and loss tangent tan δ are measured with a Q-meter at 12 MHz in the perpendicular [⊥] and parallel [//] directions to the forging axis, and considerable anisotropies, such as es[⊥]/es[//]=5 at the Curie temperature of about 680°C, are seen. The remanent polarization Pr is calculated for both cases of perfect (f=1) and random (f=0) grain orientations. Observed Pr values from hysteresis loops are smaller than calculated ones, the ratio of the former to the latter being about 82% for the hot-forged ceramics.
386 citations
TL;DR: In this article, an approximate analytic solution of the differential equation for magnetization in a cooling system gives for TB:e (TB)/kT = 1n(1.78Cθ) where e is the activation energy for rotation of magnetic moments, k is Boltzmann's constant, and C is the frequency factor (∼1010 Hz).
Abstract: Acquisition of TRM by a cooling assemblage of identical monodomain grains involves a transition from superparamagnetic to blocked behavior over a narrow but indefinite range of temperature. Blocking temperature may, nevertheless, be precisely defined by comparing the blocked magnetization, after cooling, with the curve of equilibrium magnetization against temperature. At the blocking temperature TB the relaxation time τ of the magnetization is of the same order as the cooling time constant θ, which is the time required for τ to increase by a factor e. An approximate analytic solution of the differential equation for magnetization in a cooling system gives for TB:e (TB)/kT = 1n(1.78Cθ) where e is the activation energy for rotation of magnetic moments, k is Boltzmann's constant, and C is the frequency factor (∼1010 Hz). Because e varies with temperature, the cooling time constant θ is given by 1/θ = (1/kTB)(de/dT - e/TB)dT/dt. The 95% blocking interval is about 7.2θ. For steady cooling it is reasonable to assume θ to be constant through this interval; small deviations from constancy have a negligible effect upon TB. In small external fields the variable grain geometry to be found within a real assemblage can be incorporated in a parameter e0, which is the activation energy at O°C. Curves of e0 against TB for magnetite and haematite, at cooling rates from 6°C per minute to 3°C per million years, show that (1) a change in e0 by a factor of 2 corresponds to 12 orders of magnitude change in cooling rate and (2) for a broad distribution of grain sizes a large proportion of the size range will acquire their magnetization within 100°C–200°C of the Curie point. Using these curves, blocking temperature in cooling assemblages can be related to laboratory demagnetization temperatures; the differences are greater at slower cooling rates and lower temperatures and tend to zero as the Curie temperature is approached. Intensity of magnetization should increase by a few percent for each order of magnitude decrease in cooling rate. Magnetization acquired at temperatures near the Curie point should dominate in a chemically homogenous monodomain assemblage with a broad spread of grain sizes. Possible tests of the theory and its application to the determination of cooling history are discussed.
219 citations
TL;DR: The Hall coefficient and resistivity of the first-row transition-metal intercalates, M1/3TaS2 (M = V, Cr, Mn, Fe, Co, Ni) and Fel/4NbSe2 have been measured as a function of temperature.
Abstract: The Hall coefficient and resistivity of the first-row transition-metal intercalates, M1/3TaS2 (M = V, Cr, Mn, Fe, Co, Ni), Mnl/4TaS2, M1/3NbS2 (M = V, Cr) and Fel/4NbSe2 have been measured as a function of temperature. These intercalation complexes show either ferromagnetic or antiferromagnetic orderings and there are large anomalies in both transport properties at the respective magnetic-ordering temperatures. The Hall coefficient in the ferromagnetic intercalates varies linearly with the magnetic susceptibility for temperatures above the Curie temperature, Tc, and as the square of the resistivity for temperatures below Tc. We have observed that the Hall coefficient of Fe1/3TaS2 varies non-linearly with the applied field near the Curie temperature. We have found a similar variation of the spin-disorder resistivities of the complexes, M1/3TaS2 and M1/3NbS2 (M = Mn, Fe, Co, Ni) with the intercalate ion.
209 citations
127 citations
TL;DR: The temperature dependence of elastic, dielectric, and piezoelectric constants for the film of 55/45% VDF-TrFE copolymer suggests that the Curie temperature exists at about 70°C as discussed by the authors.
Abstract: The measurement of the temperature dependence of elastic, dielectric, and piezoelectric constants for the film of 55/45% VDF‐TrFE copolymer suggests that the Curie temperature exists at about 70 °C. The lattice spacing sharply changes at a temperature range from 55 to 75 °C. The remanent polarization is also determined from the D versus E hysteresis loop below 75 °C. It is found that the spontaneous strain in crystal lattice is linearly related to the square of remanent polarization. The transition is ascribed to electrostriction due to dipolar orientation.
105 citations
TL;DR: In this paper, a spin-fluctuation theory was applied to iron and nickel for a discussion of their magnetic and thermodynamical properties at finite temperatures with a slight extension including the effect of charge fields within the steepest-descent approximation.
Abstract: A spin-fluctuation theory developed previously by the present author is applied to iron and nickel for a discussion of their magnetic and thermodynamical properties at finite temperatures with a slight extension including the effect of charge fields within the steepest-descent approximation. The Curie temperature, the average magnetization, the amplitude of local magnetic moments, the spin susceptibility and the specific heat are calculated, which are in qualitatively, or semi-quantitatively good agreement with experimental data.
101 citations
TL;DR: A detailed investigation on the thermal expansion, magnetic properties and electrical resistance of rapidly quenched amorphous (Fe,Co,Ni)-Zr alloys has been undertaken in this article.
Abstract: A detailed investigation on the thermal expansion, magnetic properties and electrical resistance of rapidly quenched amorphous (Fe,Co,Ni)-Zr alloys has been undertaken. Magnetic properties of these alloys are reported separately in this conference. The thermal expansion curves exhibit typical invar characteristics below the Curie temperature due to positive spontaneous volume magnetostriction us similar to those for Fe-Ni crystalline invar alloys. The reduced magnetization decreases strongly with increasing temperature being analogous to the case of other amorphous invar alloys. Moreover, w s at 0 K and electrical resistance at room temperature and Liq. N 2 temperature increase in the invar region. Amorphous ternary alloys of (Fe,Co, Ni) 90 Zr 10 with about 72 at% Fe have the invar characteristics in a wide temperature range and in this composition range, the volume magnetostriction and electrical resistance show maximum values of about 1.5 × 10-2and 160 μΩcm respectively.
85 citations
TL;DR: In this paper, the authors measured the magnetic susceptibility x as a function of field and temperature for the intermetallic compounds LaNi5, FeTi and Mg2Ni in the form of bulk material and of activated powder in the hydrogenated and dehydrogenated states.
Abstract: We measured the magnetic susceptibility x as a function of field and temperature for the intermetallic compounds LaNi5, FeTi and Mg2Ni in the form of bulk material and of activated powder in the hydrogenated and dehydrogenated states.
LaNi5, FeTi and Mg2Ni are Pauli paramagnets with bulk susceptibilities of 4.6 × 10−6, 3.4 × 10−6 and 0.9 × 10−6 emu g−1 respectively. The three compounds show segregation of lanthanum, titanium and magnesium respectively in a surface layer and the formation of ferromagnetic particles of nickel or iron. Because the bulk is only weakly magnetic and the specific surface area of the powders is large, the surface precipitates of nickel and iron dominate the magnetism of the powders. We checked these surface decomposition effects by measuring the Curie temperature of the precipitates and found the Curie temperatures of nickel in LaNi5 and Mg2Ni powders and that of iron in FeTi powder. The nickel precipitates are superparamagnetic at room temperature and ferromagnetic at 4.2 K. By fitting the magnetization curve with the Langevin function we calculated the size of the superparamagnetic nickel and iron precipitates (6000 nickel atoms in LaNi5, 2000 iron atoms in FeTi).
Hydrogenation reduces the bulk susceptibility of LaNi5, FeTi and Mg2Ni.
85 citations
TL;DR: In this article, a Prussian blue type compound of the stoichiometric composition Mn(CN)3⋅xH2O (x=0.57) is formed as the final product of hydrolysis of Na3[Mn(CN)] in perchloric acid.
Abstract: A Prussian blue type compound of the stoichiometric composition Mn(CN)3⋅xH2O (x=0.57) is formed as the final product of hydrolysis of Na3[Mn(CN)6] in perchloric acid. IR and visible spectra as well as structural and magnetic data show that it is a mixed valence compound consisting of sixfold N‐coordinated Mn(II) and sixfold C‐coordinated Mn(IV) in a cubic face‐centered lattice. The compound exhibits ferrimagnetism with a Curie temperature of 48.7 K. A molecular field treatment assuming two collinear spin sublattices provides an adequate description of the observed magnetic behavior. The calculation of exchange integrals, which was based on a Heisenberg model, reveals that the magnetic ordering is almost exclusively induced by an antiferromagnetic interaction between Mn(II) and Mn(IV) ions. This interaction is described in terms of a super exchange involving cyanide as bridging ligand.
TL;DR: In this article, the magnetic properties of melt-quenched amorphous ribbons having the general composition TM 100-x Zr x (TM= Fe,Co and/or Ni) have been investigated.
Abstract: Magnetic properties of melt-quenched amorphous ribbons having the general composition TM 100-x Zr x (TM= Fe,Co and/or Ni) have been investigated. Composition dependence of Curie temperature, Tc and magnetic moment, n B in Co 100-x Zr x and Ni 100-x Zr x alloys is similar to Co- and Ni-metalloid amorphous alloys. However, the decrement of Zr content in the Fe 100-x Zr x alloys causes both Tc and n B to decrease, and n B extrapolates at x=0 to almost 0 μ B . Such an unusual behavior of Tc and n B is also found on the Fe-rich portion of (Fe-Co-Ni) 90 - Zr 10 ternary system and Tc and n B of the Fe 90 Zr 10 alloy are 243 K and 1.29 μ B /Fe atom, respectively. For the Co 90 Zr 10 alloy the value of longitudinal linear magnetostriction λ is +3 × 10-6, and the zero-magnetostrictive composition lies near (Co .88 Ni .12 ) 90 Zr 10 and shifts to Fe-rich side with increasing Ni content.
TL;DR: In this paper, the susceptibility, magnetization, electrical resistivity and thermopower of Y 4 Co 3 have been measured and a Curie temperature of (8±1) K has been observed.
TL;DR: In this paper, the shape of the miscibility gap is not parabolic but of a peculiar shape, protruding to the Fe side along the Curie temperature, and the part of the protrusion is called the ridge.
Abstract: The miscibility gap of an Fe-Cr-Co system is further examined by monitoring the microstructures and the magnetic properties of the alloys. It is shown that the shape of the miscibility gap is not parabolic but of a peculiar shape, protruding to the Fe side along the Curie temperature. The part of the protrusion of the miscibility gap is called the "ridge" because of its shape resemblance. It is demonstrated that the alloys in the ridge region can exhibit very good magnetic properties. An Fe-25%Cr-12%Co alloy gives the magnetic properties as Br = 1.45 T(14.5 kG), bHc = 50.1 kA/m (630 Oe) and (BH)max = 61.3 kJ/m3(7.7 MG . Oe), which are almost comparable to those of the columnar Alnico 5 magnets.
TL;DR: In this paper, the structural relaxation of ferromagnetic glasses containing about 20at.% metalloid has been studied by using differential scanning calorimetry to measure the Curie temperature (T c ).
Abstract: The structural relaxation of ferromagnetic glasses containing about 20at.% metalloid has been studied by using differential scanning calorimetry to measure the Curie temperature (T c ). The kinetics of the T c changes on annealing are shown to depend not only on the annealing temperature, but also on the direction of the change: the change in T c is slower in a structure with a lower fictive temperature. A series of isochronal anneals on FeB, FeNiB, FePB and FeNiPB glasses suggests that, whilst the addition of a second transition metal roughly doubles the rise of T c on annealing at a given T/T x , the metalloids broaden and shift to lower T/T x the temperature range over which relaxation occurs. Care has to be exercised in interpreting the T c changes, since they may be due, not only to structural relaxation, but also to primary crystallisation and phase separation: anomalous results are obtained from FeMoB and FePB glasses. In a FeB glass cold-rolling appears to have no effect on the T c changes induced by subsequent annealing. Interpretations of the T c changes are considered both in terms of specific mechanisms and in terms of glass relaxation in general.
TL;DR: In this paper, the ferromagnetic Curie temperature, Tc, is measured by differential scanning calorimetry (DSC), which is convenient and accurate if temperature lags are corrected for.
TL;DR: In this article, the Faraday law of electromagnetic induction is applied to toroidal samples of ferrimagnetic compounds and the measurements can be performed at frequencies from 1 to 100 kHz and temperatures from 80 to 900K.
Abstract: The apparatus described is based on the Faraday law of electromagnetic induction and is especially suited for toroidal samples of ferrimagnetic compounds. The measurements can be performed at frequencies from 1 to 100 kHz and temperatures from 80 to 900K. In addition to the initial permeability and the Curie temperature, this apparatus provides a qualitative determination of the chemical homogeneity of the samples.
TL;DR: In this article, the magnetization vs temperature relation for amorphous alloys Fe 100-x B x, Fe 84 B 16-x C x, Fe 80 B 20-x Si x, etc.
TL;DR: In this paper, the weak field ac susceptibility and resistivity of Fe 2 P single crystals were measured as functions of temperature from 4.2 to 300 K and as function of hydrostatic pressures up to 20 kbar.
TL;DR: In this article, the saturation magnetisation, Curie temperature and size effects for amorphous iron alloys are reported for Fe-X, where X is one of, or a combination of, B, Al, Ga, C, Si, Ge and P. This common curve follows semiquantitatively from results obtained on the basis of the itinerant electron model.
Abstract: Measurements of the saturation magnetisation, Curie temperature and size effects are reported for the amorphous iron alloys Fe-X, where X is one of, or a combination of, B, Al, Ga, C, Si, Ge and P. The saturation magnetisation when plotted as a function of the total metalloid content shows an approximate trend in terms of charge transfer from the metalloid to iron atoms. The Curie temperature data show an approximate coincidence when plotted against X except for Fe-B-Al and Fe-B-Ge. This common curve follows semiquantitatively from results obtained here on the basis of the itinerant electron model. The relative change of volume dln V/dx was found to vary systematically with the effective valency of the added metalloid.
TL;DR: The results of small-angle ($0.025lQl0.125${\mathrm{\AA{}}}^{\ensuremath{-}1}$) neutron scattering measurements on dilute ferromagnetic alloys are presented in this paper.
Abstract: The results of small-angle ($0.025lQl0.125$ ${\mathrm{\AA{}}}^{\ensuremath{-}1}$) neutron scattering measurements on dilute ferromagnetic $\mathrm{Pd}\mathrm{Fe}$ (0.25, 0.5, 1, and 2 at.%) and $\mathrm{Pd}\mathrm{Mn}$ (0.5 and 2 at.%) alloys are presented. Critical scattering has been clearly observed in a wide temperature interval around the Curie temperature, which for $Tg{T}_{C}$ could be described by the usual Ornstein-Zernike formalism, but for $Tl{T}_{C}$ exhibited an extra quasicoherent scattering. Both the temperature and magnetic field dependence of this additional scattering could be explained by the presence of randomly oriented ferromagnetic clusters or microdomains. It is found that a distribution of cluster sizes is necessary to describe the observed scattering. The included magnetic polarization associated with the individual giant moments in $\mathrm{Pd}\mathrm{Fe}$ is obtained from the anisotropic scattering in a magnetic field and gave an average spatial extent of about 50 \AA{}. A comparison of the macroscopic magnetization and the neutron scattering results is made. A modified percolation type of model has been employed to describe the ferromagnetic ordering process, and evidence is provided that the giant moment systems can be characterized as a special case among the more general spin-glass systems.
TL;DR: In this article, the thermal expansion data of a number of ferromagnetic alloys are reconsidered in the light of the statements of Moriya and Usami that they support the spin fluctuation model of itinerant electron magnetism.
TL;DR: In this article, the enhancement factor due to magnetovolume coupling in the compressibility, high-field susceptibility and forced volume magnetostriction was estimated from the experimental data for various itinerant electron ferromagnets.
TL;DR: An X-ray single-crystal structure determination (R = 0.0397) shows that CsMnF4 crystallizes in the CsFeF4-type layer structure (tetragonal, space groupP4nmm, a = 794.40(6)pm, c = 633.76(9)pm), Z = 4).
TL;DR: In this paper, the magnetic and magneto-optic properties of amorphous (Gd 0.26 Fe 0.74 ) 1-y Sn y alloys having perpendicular uniaxial anisotropy were examined.
Abstract: We have examined the magnetic and magneto-optic properties of amorphous (Gd 0.26 Fe 0.74 ) 1-y Sn y alloys having perpendicular uniaxial anisotropy. Films were prepared by e-gun evaporation. Further interest was directed to the thermal stability and the switching properties of these films. From the temperature dependence of the saturation magnetization the compensation temperature is found to decrease strongly with increasing y while the Curie temperature is less affected. The magneto-optic Faraday and Kerr rotation investigated in the temperature range 4.2K \leq T \leq T_{C} exhibit a considerable increase with increasing Sn-content. The temperature behavior can be interpreted in terms of the mean field analysis indicating a strong reduction of the exchange constants and a stronger localization of the iron spin. Upon annealing to 1100K in air the GdFeSn films show characteristic changes of magnetic and magneto-optic properties. The addition of Sn tends to improve the thermal stability. The heat distribution in the magnetic layer and the substrate were examined experimentally to understand the local reversal of magnetization during thermomagnetic switching.
TL;DR: In this paper, the effect of K2 has been incorporated in the commonly used expressions describing the dependence on K1 and Ms of μi due to rotation of magnetization and displacement of domain walls.
Abstract: For monocrystalline MnZn ferrous ferrite the magnetocrystalline anisotropy constants K1 and K2, the initial permeability μi, and the saturation magnetization Ms have been measured in considerable detail as functions of temperature T. The effect of K2 has been incorporated in the commonly used expressions describing the dependence on K1 and Ms of μi due to rotation of magnetization and displacement of domain walls. It is shown that a nonzero K2 can limit considerably the secondary maximum of μi(T) at the temperature of anisotropy compensation. The results of measurements on monocrystalline Mn0.42Zn0.44Fe2.145O4 are interpreted with the aid of the theoretical expressions obtained for μi as a function of K1, K2, and Ms. Special attention has been paid to the temperature range around the secondary maximum of μi(T) at −82 °C and the temperature range around the primary maximum of μi(T) close to the Curie temperature.
TL;DR: In this article, the properties of amorphous Fe-B-C alloys have been studied and the density of the alloys in the series Fe 84 B 16-x C x was measured and compared to calculated densities.
Abstract: The properties of amorphous Fe-B-C alloys have been studied. The replacement of boron by carbon reduces the thermal stability of alloys containing more than approximately 80-percent iron, increases the Curie temperature slightly, and decreases the slope of the magnetization-temperature curve. Thus, although the low-temperature saturation magnetization decreases on replacement of B by C, as expected, the room-temperature magnetization exhibits a broad ridge of constant saturation magnetization per gram extending from approximately Fe 80 B 20 to approximately Fe 83 B 11 C 6 . This ridge follows one of the low-temperature magnetization contours. The density of the alloys in the series Fe 84 B 16-x C x was measured and compared to calculated densities. The increase in density agrees with the calculated values and results in a slight increase in saturation magnetization per unit volume with increase in carbon. The coercivity, both as-cast and after stress relief annealing, increases on replacement of B by C. This is not understood.
TL;DR: In this article, it was shown that up to 70 kOe of applied magnetic field is necessary to obtain single domain crystals in order to obtain a single domain antiferromagnets.
Abstract: 1. (a) US, USe and UTe are ferromagnets as well as a great variety of mixed crystals. The magnetic moments are strictly confined to the 〈111〉 easy axis. Moments measured along any other axis are merely the projections of the moment induced along the 〈111〉 axis. The shape of the hysteresis loop depends critically on temperature even far below the Curie temperature, due to thermal activation of monoatomic Bloch walls. Even if the maximum magnetization is observed along the 〈111〉 direction, it is in some cases easier to reach saturation by applying a magnetic field along another axis. The observed anisotropy cannot be of a simple uniaxial nature. 2. (b) UN, UP, UAs, USb, and UBi are antiferromagnets together with many mixed crystals. Magnetic moments in the ordered state and spin structures were determined by neutron diffraction experiments. We can observed magnetic transitions in experimentally achievable fields (200 kOe for our experiments). Such measurements permit us to establish a magnetic phase diagram. In many antiferromagnets we encounter predominant domain effects. Up to 70 kOe of applied field are necessary to obtain single domain crystals.
TL;DR: Ferromagnetic and chemical long-range order in binary alloys are studied within the mean-field approximation as mentioned in this paper, and it is found that there is a strong influence of one phenomenon on the other, with either the critical order-disorder transformation temperature or the Curie temperature appreciably altered from the corresponding isolated values.
Abstract: Ferromagnetism and chemical long-range order in binary alloys are studied within the mean-field approximation. The ordering process is driven by pairwise interatomic forces and the magnetic interactions are of the Ising type. Only nearest-neighbour forces are included. It is found that there is a strong influence of one phenomenon on the other, with either the critical order-disorder transformation temperature or the Curie temperature appreciably altered from the corresponding isolated values. The interplay of the two phenomena yields in some cases unusual sequences of phases as a function of temperature. The case of CoxFe1-x alloy is examined along these lines and it is found that the phase diagram can be well reproduced for 0.3