Showing papers on "Curie temperature published in 1988"
TL;DR: In this article, a structure determination was made for NdFe 10 Mo 2, showing that the molybdenum atoms occupied only one of the three available crystallographic sites in this structure type.
Abstract: Ternary compounds based on the tetragonal ThMn 12 structure are formed when rare earth. elements (R) are combined with iron and elements M (M ≡ Si, Ti, V, Cr, Mo or W). A structure determination was made for NdFe 10 Mo 2 , showing that the molybdenum atoms occupy only one of the three available crystallographic sites in this structure type. Detailed investigations of the systems YFe 12 − x V x showed that there is a substantial range of solid solubility extending approximately from x = 1.5 to x = 3. Curie temperatures were determined for the two series YFe 10 M 2 and GdFez 10 M 2 and were found to depend strongly on the component M.
266 citations
01 Jan 1988
TL;DR: Legvold et al. as discussed by the authors measured the basal plane magnetostrictions of Tb and Dy at low temperatures, which are 100 to 10000 times typical magnetostrains and still remain the largest known (~1%).
Abstract: By the early 1960’s, it was widely recognized that the rare earths possessed many extraordinary magnetic properties. Neutron diffraction measurements, for example, showed that the spin structures were much more complex than those of any of the classical ferromagnets or antiferromagnets. More importantly, in the heavy rare earth metals, the parallel coupling of large orbital and large spin angular momenta yielded huge magnetic moments of 9μ B and 10μ B, dwarfing the conventional values of 0.6 for Ni and 2.2 for Fe. Enormous magnetic anisotropies were also encountered in the heavy rare earth elements. In 1963, a breakthrough in magnetostrictive materials occurred with the measurement of the basal plane magnetostrictions of Tb and Dy at low temperatures (Legvold et al. 1963, Clark et al. 1963, 1965, Rhyne and Legvold 1965). These basal plane strains are 100 to 10000 times typical magnetostrictions and still remain today the largest known (~1%). Over wide temperature ranges, thermal expansions are dominated by the temperature dependences of the magnetostrains. Elastic moduli were found to be strongly influenced by the unprecedented magnetoelastic interactions. However, because of the low ordering temperatures of the rare earths the application of these magnetostrictive properties to devices operating at room temperature could not be achieved with the elements. Only Gd, which is essentially non-magnetostrictive, possesses a Curie point as high as room temperature.
240 citations
TL;DR: In this paper, it was shown by X-ray diffraction that rare earth compounds of the type R2Fe17 can dissolve appreciable amounts of carbon up to x = 0.6 in R 2Fe17Cx at 900 °C.
Abstract: It was shown by X-ray diffraction that rare earth compounds of the type R2Fe17 can dissolve appreciable amounts of carbon up to x = 0.6 in R2Fe17Cx at 900 °C. The increase in the lattice constants is accompanied by a strong increase in Curie temperature. From a structure determination (R = 7%) it was found that the carbon atoms dissolve interstitially and occupy the 9e position in the Th2Zn17 structure type (R3m). This ternary carbide is present as the main phase when compounds of the type R2Fe14C are heated above their decomposition temperatures. The decomposition proceeds by means of a solid state transformation and the corresponding transformation temperatures Tt vary strongly with the R component. In several of the light rare earth systems Tt becomes rather low and makes an annealing treatment ineffective with regard to the formation of R2Fe14C phases. The magnetic properties of the R2Fe14C phases are compared with those of R2Fe14B. It is shown that the former follow the magnetic behaviour of the latter almost completely.
225 citations
TL;DR: The extended McConnell model was developed and provides the synthetic chemist with guidance for making new molecular materials to study cooperative magnetic coupling in systems and a model of configuration mixing of the lowest charge-transfer excited state with the ground state was developed.
Abstract: Quantitative bulk ferromagnetic behavior has been established for the molecular/organic solid [Fe(III)(C(5)Me(5))(2)].(+)[TCNE].(-). Above 16 K the dominant magnetic interactions are along a 1-D chain and, near T(c), 3-D bulk effects as evidenced by the value of the critical exponents dominate the susceptibility. The extended McConnell model was developed and provides the synthetic chemist with guidance for making new molecular materials to study cooperative magnetic coupling in systems. Assuming the electron-transfer excitation arises from the POMO, ferromagnetic coupling by the McConnell mechanism requires stable radicals (neutral, cations/anions, or ions with small diamagnetic counterions) with a non-half-filled POMO. The lowest excited state formed via virtual charge transfer (retro or forward) must also have the same spin multiplicity and mix with the ground state. These requirements limit the structure of a radical to D(2d) or C>/=(3) symmetry where symmetry breaking distortions do not occur. Intrinsic doubly and triply degenerate orbitals are not necessary and accidental degeneracies suffice. To achieve bulk ferromagnetism, ferromagnetic coupling must be established throughout the solid and a microscopic model has been discussed. These requirements are met by [Fe(III)(C(5)Me(5))(2)].(+)[TCNE].(-). Additionally this model suggests that the Ni(III) and Cr(III) analogs should be antiferromagnetic and ferrimagnetic, respectively, as preliminary data suggest. Additional studies are necessary to test and further develop the consequences of these concepts. Some molecular/organic solids comprised of linear chains of alternating metallocenium donors (D) and cyanocarbon acceptors (A) with spin state S = 1/2 (...D.(+)A.(-)D.(+)A.(-)...) exhibit cooperative magnetic phenomena, that is, ferro-, antiferro-, ferri-, and metamagnetism. For [Fe(III)(C(5)Me(5))(2)].(+)[TCNE](-). (Me = methyl; TCNE = tetracyanoethylene), bulk ferromagnetic behavior is observed below the Curie temperature of 4.8 K. A model of configuration mixing of the lowest charge-transfer excited state with the ground state was developed to understand the magnetic coupling as a function of electron configuration and direction of charge transfer. This model predicts that ferromagnetic coupling requires stable radicals with a non-half-filled degenerate valence orbital and a charge-transfer excited state with the same spin multiplicity that mixes with the ground state. Ferromagnetic coupling must dominate in all directions to achieve a bulk ferromagnet. Thus, the primary, secondary, and tertiary structures are crucial considerations for the design of molecular/organic ferromagnets.
197 citations
TL;DR: Theoretic generalization of ferromagnetic ordering in low and three-dimensional organic substances has been achieved as discussed by the authors, and a number of 3D carbon structures have been forwarded.
138 citations
TL;DR: In this paper, the authors investigated ternary compounds based on the tetragonal ThMn12 structure where M is Ti, Si, V, Cr, and Mo.
Abstract: Sm(Fe1−xMx)12 ternary compounds based on the tetragonal ThMn12 structure where M is Ti, Si, V, Cr, and Mo were investigated. M atoms have a preference for site occupation. Ti atoms occupy the 8i or 8j site and Cr atoms occupy the 8i site. Curie temperatures on Sm(M,Fe)12 compounds are around 590 K except for the SmMo2Fe10 compound (Tc=483 K). The SmTiFe11 and SmSi2Fe10 compounds have a high saturation magnetization and magnetic anisotropy.
130 citations
TL;DR: The validity of nucleation and domain wall pinning models has been examined in R•Fe•B magnets by correlating the hard magnetic properties with the microstructure and magnetic domain structure as mentioned in this paper.
Abstract: The validity of nucleation and domain wall pinning models has been examined in R‐Fe‐B magnets by correlating the hard magnetic properties with the microstructure and magnetic domain structure The nucleation model can be used to explain the magnetic properties of R‐Fe‐B magnets at low temperatures, but it fails at high temperatures On the other hand, domain wall pinning can explain the magnetic properties over a much wider temperature range (up to the Curie temperature) The magnetic and structural data suggest that the coercivities (Hc) of powders and stoichiometric melt‐spun ribbons are due to ‘‘strong pinning’’ by a random distribution of pins while the Hc of sintered magnets and ribbons with off‐stoichiometric composition are due to ‘‘localized pinning’’ at grain boundaries
127 citations
TL;DR: In this article, thin films of ferroelectric Pb1−xCaxTiO3 (x=0.0-0.4) were formed on MgO, Pt/MgO and SrTiO 3 substrates by rf magnetron sputtering.
Abstract: Thin films of ferroelectric Pb1−xCaxTiO3 (x=0.0–0.4) were formed on MgO, Pt/MgO, SrTiO3, and Pt/SrTiO3 substrates by rf magnetron sputtering. Characterization of the films by x‐ray diffraction, x‐ray precession, scanning electron microscopy, and electron probe microanalysis showed them to be epitaxially grown with their c‐axis oriented perpendicular to the substrate. The decrease in the Curie temperature Tc and the increase in the pyroelectric coefficient dPs/dT with an increase in Ca doping were successfully explained by assuming that the Ca ions occupied Pb ion sites. Pyroelectric infrared detectors using Pb0.7Ca0.3TiO3 thin‐film elements gave better performance than the detectors using PbTiO3 ceramic elements. The internal bias field EB and fixed polarization PB were observed to be a function of both the Ca content and temperature in ferroelectric hysteresis curves as well as in hysteresis curves of the dielectric constant as a function of the applied electric field. These phenomena were explained by t...
117 citations
TL;DR: In this paper, the preparation and magnetic properties of ThMn12-type phases R,Fe,Mo,(Co), R=Y, Ce, Nd, Sm, Gd, Dy, Er are described.
Abstract: Preparation and magnetic properties of ThMn12‐type phases R,Fe,Mo,(Co), R=Y, Ce, Nd, Sm, Gd, Dy, Er are described. The ternary material, without Co, exhibits saturation magnetization up to 1 T and Curie temperature up to 215 °C, the quaternary material, with Co, up to 1.2 T, and 295 °C, respectively.
112 citations
TL;DR: In this article, a serial radio-frequency sputter-microsectioning method with radioactive tracers 55Fe and 59Fe in the temperature range 766-1148 K was used to study the self-diffusion and isotope effect in α-iron.
110 citations
TL;DR: In this paper, the ternary (Fe0.6Pt0.4)100−xBx and (Fe1−yPty)83B17 alloy ribbons prepared by the twin roll technique were investigated.
Abstract: Magnetic properties were investigated for the ternary (Fe0.6Pt0.4)100−xBx and (Fe1−yPty)83B17 alloy ribbons prepared by the twin roll technique. Boron changes the compositions of the ordered FePt (γ1) phase, which coexists with Fe2B at various alloy compositions so that the actual Pt content of γ1 in the ternary alloy goes up with increasing boron content. Coercive force increase due to boron addition is remarkable, in particular at low Pt concentration. Annealing time to get high coercivity becomes much shorter by boron addition. iHc=5.6 kOe and 4πMs=7.8 kG were obtained in the (Fe0.65Pt0.35)83B17 ribbon.
TL;DR: In this article, the Curie point temperature of solid solutions made by firing mixtures of BaTiO3 and BaZrO3 powders was found to depend markedly on sintering condition.
Abstract: The Curie point temperature of solid solutions made by firing mixtures of BaTiO3 and BaZrO3 powders was found to depend markedly on sintering conditionS. However, when the ceramic was made from a homogeneous powder, wherein each particle of powder had the same chemical composition, the Curie point temperature was only slightly dependent on the firing schedule. Using chemically homogeneous powders, Ba(Ti1−xZrx)O3 withx=0.05, 0.10 and 0.20, the Curie point temperature shift was found to be a non-linear function of x.
TL;DR: The magnetic properties of the compounds AT2P2 (A = Sr, La, Eu; T = Fe, Co) and EuNi2p2 were studied by 57Fe and 151Eu Mossbauer spectroscopy, and magnetic susceptibility measurements.
TL;DR: In this paper, the uptake of hydrogen by Nd2 Fe17 and Sm2Fe17 has been monitored in a thermopiezic analyser as a function of temperature at an initial pressure of 1 bar (105 Pa).
Abstract: The uptake of hydrogen by Nd2 Fe17 and Sm2Fe17 has been monitored in a thermopiezic analyser as a function of temperature at an initial pressure of 1 bar (105 Pa). The first stage of hydrogen absorption around 250° C yields R2Fe17H
y
(R = Nd, Sm) withy ≅ 2.2; this compound retains the Th2Zn17 structure of the starting alloy but the cell volume is increased by about 3%. The Curie temperature increases from 57 to 175° C for R = Nd and from 115 to 253° C for R = Sm. A second stage of hydrogen absorption at about 600° C corresponds to disproportionation of the alloy into α-Fe + RH2−ɛ.
TL;DR: In this article, the compositional variation of saturization magnetization and Curie temperature for Ni1−y−xZnxCuyFe2O4 where x = 0.0, 0.6, 0., 0.8, 1.0 for y = 0 and x =0.2 have been reported.
TL;DR: In this paper, the magnetic and crystallographic properties of the RFe/sub 10/T/sub 2/ compounds are discussed together with the properties of 3d-rich ternary compounds of different composition and structure.
Abstract: The crystal structure and the magnetic properties are determined for several novel ternary intermetallic compounds of the type RFe/sub 10/T/sub 2/, where R represents Ti, V, Cr, Mo, W, or Si. All these compounds show a strong ferromagnetic behavior, with Curie temperatures in the range 350 K to 600 K. The magnetic and crystallographic properties of the RFe/sub 10/T/sub 2/ compounds are discussed together with the properties of 3d-rich ternary compounds of different composition and structure. Special attention is paid to the magnetocrystalline anisotropy of these materials, consisting of contributions of the R sublattice and the Fe sublattice. Detailed information on the crystal-field-induced contribution of the former sublattice is derived from /sup 155/Gd Mossbauer spectroscopy performed on the Gd compounds of these series, since the /sup 155/Gd nucleus can be regarded as a sensitive probe of the electric field gradient at the nuclear site produced by the electric charges of the surrounding ions. It can be shown that this electric field gradient is proportional to the second order crystal field parameter A/sup 0//sub 2/, which in turn determines the magnetocrystalline anisotropy of the R sublattice. >
TL;DR: In this paper, the Ni1−x Znx Fe2O4 (0≤x≤1) using novel hydrazinium metal hydrazinecarboxylate precursors.
Abstract: Nickel zinc ferrites have been very widely used in the high‐frequency applications. In our present study we have prepared Ni1−x Znx Fe2O4 (0≤x≤1) using novel hydrazinium metal hydrazinecarboxylate precursors. High densities (∼99%) have been obtained for all the ferrites sintered at relatively low temperatures, 1100 °C, in comparison with the conventional method (≥1200 °C). The variation of magnetic properties like magnetic moment, Curie temperature, and permeability with zinc concentration have been studied.
TL;DR: In this article, the pyrochlores of the type R2Mn2O7 have been characterized where R is Dy, Ho, Er, Tm, Yb, Lu, or Y. All are semiconductors with activation energies ranging from 0.37 to 0.51 eV, which correlate well with the electronegativity of R.
TL;DR: In this article, the magnetic order at surfaces of the 4f rare earth metal terbium was investigated using electron capture spectroscopy (ECS), which probes the electron spin polarization (ESP) of the topmost surface layer.
Abstract: The magnetic order at surfaces of the 4f rare‐earth metal terbium is investigated using electron capture spectroscopy (ECS), which probes the electron spin polarization (ESP) of the topmost surface layer. In ECS, the capture of spin‐polarized electrons during grazing‐angle ion‐surface interaction is used to determine the ESP due to long‐ and short‐ranged surface magnetic order. It is found that long‐ranged ferromagnetic order exists far above the bulk Curie temperature, measured to be TCb =220 K. At 140 K, the long‐ranged ESP amounts to 24%. With increasing temperature, the ESP first decreases montonically up to the bulk Neel temperature TNb=228 K, then exhibits a pronounced maximum at T=238 K, and ultimately vanishes at the surface Curie temperature TCs =248 K. These striking results on enhanced magnetic order at Tb surfaces suggest the presence of very large surface anisotropies.
Patent•
18 Mar 1988
TL;DR: In this paper, an alloy which permits quantitative thermal decomposition of the entire sample at the Curie point temp is obtained by mixing the granular ferromagnetic alloy with the flaky sample and molding the same to a prescribed shape, then using such molding.
Abstract: PURPOSE:To obtain an alloy which permits quantitative thermal decomposition of the entire sample at the Curie point temp. of the alloy by mixing the granular ferromagnetic alloy with the flaky sample and molding the same to a prescribed shape, then using such molding. CONSTITUTION:The sample 2 of the flaky or powder org. high-polymer compd. is dispersed into the granular ferromagnetic alloy 1 and is molded by pressing. The alloy 1 and the org. high-polymer compd. of the sample are thereby thoroughly and tightly adhered to each other and the entire sample is heated up to the Curie point possessed by the alloy in the extremely short time, by which the quantitative thermal decomposition at said temp. is permitted.
TL;DR: In this article, the dielectric and electrical properties of Ba 1− x Sr 2+ on the Curie point of BaTiO 3 and the role of compositional inhomogeneity caused in the solid solutions on their electrical resistivity were investigated.
TL;DR: In this article, Icosahedral quasi-crystals with coercivity at room temperature are found in rapidly solidified Al-Ge-Mn and Al-Cu-Ge -Mn alloys with compositions ranging form 20 to 25 at%Ge, 22.5 to 25%Mn, and 0 to 10%Cu.
Abstract: Icosahedral quasi-crystals with coercivity at room temperature are found in rapidly solidified Al-Ge-Mn and Al-Cu-Ge-Mn alloys with compositions ranging form 20 to 25 at%Ge, 22.5 to 25%Mn and 0 to 10%Cu. The highest Curie temperature is 533 K for Al52.5Ge22.5Mu25 and 467 K for Al40Cu10Ge25Mn25. The magnetization ( σ20) of the Al-Ge-Mn alloys in a field of 20 kOe at room temperature increases from 0.2 to 0.5 emu/g with increasing Ge and Mn contents and the coercivity (Hc) is in the range of 0.7 to 1.1 kOe. The replacement of Al by 10%Cu is found to bring about significant increases of σ20 and Hc to 3.9 emu/g and 1.8 kOe.
TL;DR: Ferroelectric PbTiO/sub 3/ films 0.5- to 2.0- mu m thick were prepared by the metalloorganic decomposition (MOD) process using multilayer spinning with firing temperatures of 490-630 degrees C as discussed by the authors.
Abstract: Ferroelectric PbTiO/sub 3/ films 0.5- to 2.0- mu m thick were prepared by the metalloorganic decomposition (MOD) process using multilayer spinning with firing temperatures of 490-630 degrees C. The temperature dependence of the dielectric constant was found to be a function of the c/a ratio, which could be modified by control of either the single-layer thickness or the strength of the electric field during film preparation near the Curie temperature. The films were near theoretical density and defect-free over 2 cm*2 cm areas. >
TL;DR: In this paper, the temperature dependence of the longitudinal ultrasonic velocity in iron and Dural has been obtained using a totally remote laser technique, which is generated by irradiation of one face of a sample with a Q-switched Nd:YAG laser pulse and is detected on the opposite face using a modified Michelson laser interferometer.
Abstract: The temperature dependence of the longitudinal ultrasonic velocity in iron and Dural has been obtained using a totally remote laser technique. The ultrasound is generated by irradiation of one face of a sample with a Q‐switched Nd:YAG laser pulse and is detected on the opposite face using a modified Michelson laser interferometer. The system has proved capable of measurements up to temperatures in excess of 1000 °C, with an absolute accuracy in velocity of ±1%, and relative accuracies of better than 0.1%. Anomalies in the data for iron have been discerned at the Curie temperature of ∼768 °C, due to the ferromagnetic to the paramagnetic phase transition, and at 910 °C due to the crystallographic phase transition from ferrite to austenite.
TL;DR: The rare-earth-iron intermetallic compounds SmTiFex, with x ranging between 8 and 10, have been synthesized by an arc melting technique as discussed by the authors, and they crystallize in the ThMn12-type tetragonal structure, I4/mmm Unusual uniaxial magnetocrystalline anisotropies have been observed.
Abstract: The rare‐earth–iron intermetallic compounds SmTiFex, with x ranging between 8 and 10, have been synthesized by an arc‐melting technique We found that they crystallize in the ThMn12‐type tetragonal structure, I4/mmm Unusual uniaxial magnetocrystalline anisotropies have been observed The c axis is the easy magnetization direction Curie temperature is 610 K After the discovery of the R2Fe14B compounds, we have other ternary rare‐earth–iron intermetallic compounds with strong uniaxial anisotropy
TL;DR: In this article, the authors evaluated both rare earth and transition metal sublattice contributions to the magnetocrystalline anisotropy, and compared the Fe and Co anisotropies in the ThMn12 tetragonal crystal structure.
Abstract: Intermetallic compounds of the type RE(TM1−xMx)12 with RE=Y, Er; TM=Fe, Co; M=Si, Ti, V of the ThMn12 tetragonal crystal structure have been studied by the singular point detection technique and high‐resolution neutron powder diffraction in order to (a) evaluate both the rare‐earth and transition‐metal sublattice contributions to the magnetocrystalline anisotropy, (b) compare the Fe and Co anisotropies in the ThMn12 structure, and (c) to verify the existence of any preferential entrance in the transition metal sublattice for various stabilizing ions. The transition metal anisotropy is of the same type (Fe axial, Co planar) and magnitude as in RE2Fe14B compounds. However, there is no anomalous temperature behavior of the anisotropy field Ha. With decreasing temperature, the value of Ha increases from 21 kOe at 293 K to 37 kOe at 78 K in YFe11Ti. Similar values are obtained for other Fe‐based compounds. The contribution of Er to the anisotropy is found to be surprisingly low. The anisotropy field of ErFe11T...
TL;DR: In this article, single crystals of the compounds R2Fe14B some 1-4 mm in size have been grown for a study of the anisotropy of the magnetization curves.
Abstract: Single crystals of the compounds R2Fe14B some 1–4 mm in size have been grown for a study of the anisotropy of the magnetization curves. These curves for crystals with R=Tb, Dy, Ho, Er, and Tm were measured at the Service National des Champs Intenses, Grenoble, between 4.2 and 275 K, with fields of 0–18 T being applied along the [100], [110], and [001] directions. Magnetization curves for all five compounds are analyzed in terms of the exchange and crystal field interactions (including terms up to sixth order, which may differ at 4 f and 4g sites) following the analysis previously developed for Nd2Fe14B. Molecular field coefficients representing the exchange interactions between R and Fe spins decrease from light to heavy R compounds as previously deduced from analysis of Curie temperatures. The CEF parameters are approximately the same across the series. In particular, the A20 terms are constant to within 10%.
TL;DR: In this paper, zinc and aluminum were successfully substituted in the spinel lattice and that the Curie temperature was reduced by both substitutions, and the Faraday rotation spectra of the films were measured and the difference between Coferrite, CoZn-ferrite-and CoAl-Ferrite films were discussed considering the distribution of Co2+ and Fe3+ over the lattice sites.
Abstract: Zinc- and aluminum-substituted cobalt-ferrite thin films were prepared on fused quartz substrates using vacuum evaporation followed by heat treatment. Magnetic measurements and X-ray diffraction analyses of the films showed that zinc and aluminum were successfully substituted in the spinel lattice and that the Curie temperature was reduced by both substitutions. The Faraday rotation spectra of the films were measured and the difference between Co-ferrite, CoZn-ferrite- and CoAl-ferrite films are discussed considering the distribution of Co2+ and Fe3+ over the lattice sites and the difference of the lattice constants. The performance factor of the films was improved around 800 nm by zinc substitution and around 1500 nm by aluminum substitution.
TL;DR: Raman spectroscopy of KNO3 thin-film ferroelectric memories has been performed as a function of film thickness, temperature, annealing procedures, and read-write cycles as mentioned in this paper.
Abstract: Raman spectroscopy of KNO3 thin‐film ferroelectric memories has been performed as a function of film thickness, temperature, annealing procedures, and read‐write cycles (fatigue) The results show that conversion to phase II is not the cause of failure in these memory devices, in agreement with the x‐ray results of Schaffer and Mikkola Waiting time effects are in accord with the space‐charge theory of Takahashi
TL;DR: In this article, it was shown that thin single crystals and large bulk single crystals grow in films of vinylidene fluoride and trifluoroethylene copolymers when they are annealed at temperatures between the Curie point and melting point.
Abstract: Thick lamellar single crystals and large bulk single crystals are found to grow in films of vinylidene fluoride and trifluoroethylene copolymers when they are annealed at temperatures between the Curie point and melting point. The morphologies of these crystals are studied using SEM, TEM, and X-ray diffraction. The lamellar crystals are thick (0.1 µm) enough to be characterized as extended chain crystals. They are stacked together with their planes perpendicular to the film surface. The bulk single crystals exhibit various crystal habits with the maximum size 12 × 10 × 10 µm3. They are developed on the lamellar crystals from which the constituent molecules seem to be supplied. The growth of the crystals is discussed on the basis of the diffusive displacement of the molecules along the chain axis which becomes violent above the Curie temperature.