Showing papers on "Curie temperature published in 1992"
TL;DR: It is proposed that this deviation arises due to short-range correlations between polar regions, and that these correlations at high temperatures are the precursor to a freezing of the polarization fluctuations into a glassy state.
Abstract: The deviation from Cure-Weiss behavior has been investigated in lead magnesium niobate relaxor ferroelectrics. At high temperatures, the susceptibility was found to follow the Curie-Weiss relationship. A Curie constant and temperature of 1.2\ifmmode\times\else\texttimes\fi{}${10}^{5}$ and 398 K, respectively, were obtained. With decreasing temperature the deviation was found to increase. It is proposed that this deviation arises due to short-range correlations between polar regions, and that these correlations at high temperatures are the precursor to a freezing of the polarization fluctuations into a glassy state. A local (glassy) order parameter was calculated from the susceptibility by analogy to spin glasses [D. Sherrington and S. Kirkpatrick, Phys. Rev. Lett. 35, 1972 (1975)]. These results are compared to the rms polarization [G. Burns and F. Dacol, Solid State Commun. 48, 853 (1983)] and to the measured remanent polarization. The frequency and field dependence has also been investigated.
491 citations
TL;DR: In this paper, a comparison of the static signal levels R×(θk2+ek2)1/2 of Co/Pt multilayers and alloys shows an overall 50% enhancement in the case of alloys.
Abstract: Co1−xPtx alloys with Pt contents in the range 0.45≤x≤0.9 show sizable perpendicular magnetic anisotropy, 100% perpendicular remanence and coercivities in the range 160 kA/m. Thin films of this material are grown by electron beam evaporation onto fused silica or Si, at substrate temperatures between 150 and 350 °C. Spectroscopic investigations of the polar Kerr rotation show a significant enhancement of the Pt related UV peak. A comparison of the static signal levels R×(θk2+ek2)1/2 of Co/Pt multilayers and alloys shows an overall 50% enhancement in the case of alloys. Curie temperatures around 200 °C are observed for Co∼22Pt∼78 compositions. These properties, together with the potentially high chemical stability and ease of manufacturing make Co1−xPtx alloys very attractive materials for short wavelength magneto‐optic recording.
195 citations
TL;DR: In this article, structural features in mixed Mn3+, Mn4+ perovskites, Pr1−xAxMnO3 (A = Ca, Sr, Ba) are given.
171 citations
Patent•
09 Nov 1992
TL;DR: In this paper, a magnetic recording medium made of a material having high residual magnetic flux density and coercive force and a low Curie temperature by a method wherein a vertically magnetized film in which Co/Pt artifical lattice films obtained by alternately laminating Co layers and Pt layers and Co thin films are alternately laminated is provided on a substrate.
Abstract: PURPOSE:To obtain a magnetic recording medium made of a material having high residual magnetic flux density and coercive force and a low Curie temperature by a method wherein a vertically magnetized film in which Co/Pt artifical lattice films obtained by alternately laminating Co layers and Pt layers and Co thin films are alternately laminated is provided on a substrate. CONSTITUTION:On a bendable stainless steel substrate 8, a vertically magnetized film, i.e., a multiplex-structure multilayer film 9 obtained by alternately laminating Co/Pt artifical lattice films and Co thin films, is formed by an RF sputtering method, whereby a magnetic recording medium 10 is produced. Said magnetic recording medium 10 is shaped into a sheet form to be wound on a recording magnetic drum core material 11. A Co layer and a Pt layer forming the Co/Pt artifical lattice film 9a respectively have a thickness (dCo) of 1Angstrom <=dCo<=15Angstrom and a thickness (dPt) of 2Angstrom <=dPt<=30Angstrom . On the other hand, a thickness (DCo) of the Co thin film 9b is 10Angstrom <=DCo<=1000Angstrom . In the evaluation of this magnetic recording medium 10, a coercive force is the order of 2000 Oe, a residual magnetic flux density is 1000 gauss or more, a magnetic force required for attracting a toner as a magnetic substance is sufficiently generated, and a Curie temperature is as low as 200 deg.C or lower.
147 citations
TL;DR: The magnetic properties of the low-temperature phase of MnBi, prepared by rapid solidification, have been measured in a pulsed field over the temperature range 80-625 K.
Abstract: The magnetic properties of the low-temperature phase of MnBi, prepared by rapid solidification, have been measured in a pulsed field over the temperature range 80--625 K. The anisotropy field, obtained by the singular-point-detection technique, is found to increase with temperature and has a maximum value of 9 T at 530 K. A fit to the saturation-magnetization measurement gives a virtual Curie point of 775 K. The coercive field is fitted by a hybrid domain-wall-pinning theory which yields, at 300 K, a domain-wall energy of 15.6 erg/${\mathrm{cm}}^{2}$ and a wall thickness of 70 \AA{}. Below 200 K, the presence of a ferrimagnetic phase is detected. Its critical field associated with spin reversal is a convex function of temperature having a maximum value of 8 T at 120 K.
132 citations
TL;DR: In this article, the effects of MnO2 addition on k31 and Qm were investigated for Pb(Zr0.5Ti 0.5)O3(PZT).
Abstract: The effects of MnO2 addition on k31 and Qm were investigated for Pb(Zr0.5Ti0.5)O3(PZT). The MnO2 addition increased Qm and k31 in a low poling field. This result indicated that Mn-doped PZT possessed properties of `soft' and `hard' piezoelectrics simultaneously. Electron spin resonance measurement indicated that Mn2+, Mn3+ and Mn4+ coexisted in PZT. The tetragonality of the PZT lattice and the Curie temperature decreased with MnO2 content. From these results, it was found that the increase in k31 of Mn-doped PZT was due to the change of the crystal structure toward a cubic system, and the increase in Qm to Mn2+ and Mn3+ ions working as acceptor dopants. The characteristic feature of Mn is that its addition to PZT decreases tetragonality, and various valence states coexist in proper ratio in Mn-doped PZT sintered in atmosphere.
123 citations
TL;DR: In this paper, the authors studied the Curie temperature of ferroelectric films described by the transverse Ising model under the mean-field theory and obtained the film layer number, the surface interaction and the surface layer number dependence of the curie temperature.
Abstract: The Curie temperature of ferroelectric films described by the transverse Ising model was studied under the mean-field theory. The film layer number, the surface interaction and the surface layer number dependence of the Curie temperature were obtained. There is a critical surface interaction strength, which is JSC=1.25 J for single-surface-layer films, and JSC=1.078 J for multiple-surface-layer films. If the surface interaction strength exceeds the critical value, there exists an optimum film thickness which possesses the maximum Curie temperature; then the surface interaction strength is weaker than the critical value, the Curie temperature decreases monotonically with increasing film thickness, and there exist critical sizes or critical thicknesses at which the ferroelectricity will disappear if the surface interaction is weak enough.
98 citations
TL;DR: In this paper, the magnetic and electrical properties of U 7 Ge, U 5 Ge 3, U 3 Ge 4 and UGe 2 were clarified, measuring the electrical resistivity, thermoelectric power, Hall coefficient, magnetic susceptibility, magnetization and specific heat.
Abstract: We have clarified the magnetic and electrical properties of U 7 Ge, U 5 Ge 3 , U 3 Ge 4 and UGe 2 , measuring the electrical resistivity, thermoelectric power, Hall coefficient, magnetic susceptibility, magnetization and specific heat. U 7 Ge and U 5 Ge 3 , which are Pauli paramagnetic compounds, become superconductive below 1.40 K and 0.99 K, respectively. The latter compounds U 3 Ge 4 and UGe 2 indicate ferromagnetism. Anisotropic properties of UGe 2 are well reflected in the electrical resistivity, magnetic susceptibility and magnetization.
91 citations
TL;DR: In this paper, the ferromagnetic properties of compaction-prepared nanocrystalline Ni specimens were investigated in order to study the correlation between the disordered interfacial structure and the macroscopic properties.
90 citations
TL;DR: In this article, the existence of interstitial Sm2Fe17Nx with intermediate nitrogen contents (0 ≤ x ≤ 2.94) is revealed by a continuous increase of the unit cell volume, the Curie temperature, the saturation polarization and the anisotropy field with increasing N concentration.
86 citations
TL;DR: While the transverse spin freezing and the finite spin clusters plus ferromagnetic (FM) matrix models fail to explain some of the findings, the finite-FM-clusters- FM-matrix picture provides a satisfactory explanation for all the diverse aspects of the present results.
Abstract: A detailed analysis of the magnetization and ``zero-field'' M\"ossbauer data taken on the amorphous ${\mathrm{Fe}}_{90}$${\mathrm{Zr}}_{10}$ alloy in the temperature range 4.2--300 K reveals the following: (i) Spin-wave (SW) excitations at low temperatures, single-particle (SP) excitations and local-spin-density (LSD) fluctuations over a wide range of intermediate temperatures, and enhanced fluctuations in the local magnetization for temperatures close to the Curie temperature, ${\mathit{T}}_{\mathit{C}}$, contribute dominantly to the thermal demagnetization of spontaneous magnetization; (ii) SW modes soften at temperatures below the freezing temperature ${\mathit{T}}_{\mathit{f}}$, where long-range ferromagnetic order coexists with the cluster spin-glass order; (iii) the LSD fluctuations are completely suppressed when magnetic fields (H) higher than 5 kOe are applied and M(H,T) for Hg5 kOe is solely governed by the SW and SP excitations for temperatures up to 0.95${\mathit{T}}_{\mathit{C}}$; (iv) contrary to some earlier claims, the spin-wave stiffness coefficient does not depend on H in the field range 5 kOe\ensuremath{\le}H\ensuremath{\le}15 kOe; (v) the magnetic hyperfine-field distribution, P(${\mathit{H}}_{\mathrm{hf}}$), is bimodal and comprises two Gaussian distributions; (vi) the low-field spin fraction [ratio of the area under the low-field Gaussian curve to that under the P(${\mathit{H}}_{\mathrm{hf}}$)-vs-${\mathit{H}}_{\mathrm{hf}}$ curve] grows at the expense of the high-field spin fraction as the temperature is raised above T\ensuremath{\simeq}150 K and amounts to about 90% of the total Fe spins for T\ensuremath{\simeq}${\mathit{T}}_{\mathit{C}}$; and (vii) the spin-freezing process does not start abruptly at ${\mathit{T}}_{\mathit{f}}$ but proceeds gradually over a wide temperature range extending from 130 K (\ensuremath{\approxeq}3${\mathit{T}}_{\mathit{f}}$) down to 4.2 K. While the transverse spin freezing and the finite spin clusters (composed of antiferromagnetic Fe spins) plus ferromagnetic (FM) matrix models fail to explain some of our findings, the finite-FM-clusters--FM-matrix picture provides a satisfactory explanation for all the diverse aspects of the present results.
Patent•
3M1
TL;DR: An electromagnetic radiation susceptor material comprises at least one species of particle dispersed in a dielectric binder material as mentioned in this paper, which may be applied to substrate, such as an electrically conductive material.
Abstract: An electromagnetic radiation susceptor material comprises at least one species of particle dispersed in a dielectric binder material. Any dispersed species of particle comprises a ferromagnetic amorphous alloy having the composition F 100-y-x M y TM x , where M is one or more magnetic elements selected from the group consisting of Fe, Co, and Ni; M is one or more metalloids selected from the group consisting of B, C, Al, Si, P and Ge; TM is one or more transition metal selected from the group consisting of columns IIIB (including the rare earths) to VIIB of the periodic table, and especially Ti, V, Cr, Mn, Zr, Nb, and Ta; 0≦x≦20; and 10≦y≦30. The transition metal controls the Curie temperature of the alloy to provide temperature self-regulation. Many types dielectric binder are suitable. The susceptor material may be applied to substrate, such as an electrically conductive material.
TL;DR: Angle-resolved photoemission is used to determine the temperature-dependent electronic properties of ferromagnetic bulk Gd along Γ-A of the three-dimensional Brillouin zone.
Abstract: Angle-resolved photoemission is used to determine the temperature-dependent electronic properties of ferromagnetic bulk Gd along Γ-A of the three-dimensional Brillouin zone. The Δ 2 band exchange splitting (0.85 eV) and dispersion (0.5 eV) are in reasonably good agreement with self-consistent local spin-density approximation calculations. The conduction-band magnetic exchange splitting vanishes at the Curie temperature following a conventional power law with a Heisenberg critical exponent
TL;DR: In this article, the crystal structure and magnetic properties of novel ternary compounds of the composition R 2 (Fe 0.91 V 0.09 ) 17 (R≡Y, Nd, Sm, Gd) were investigated.
TL;DR: In this article, the curie-temperature and saturation magnetization of the metallic ferromagnetic perovskite La 2 3 Ba 1 3 MnO 3 decreases, when manganese is substituted by copper.
TL;DR: A series of rare-earth iron carbides were prepared by heat treatment of R2Fe17 compounds in methane as discussed by the authors, and the nominal composition of these carbides is R 2Fe17Cx, x∼2.5 T.
Abstract: A series of rare‐earth iron carbides were prepared by heat treatment of R2Fe17 compounds in methane. The nominal composition of these carbides is R2Fe17Cx, x∼2.5. The carbides retain the original Th2Zn17 or Th2Ni17 structure with a 6.5% volume expansion over the carbon‐free unit cell. For Sm2Fe17C2.5, the Curie temperature is 760 K and the easy magnetization direction is along the c axis. The anisotropy field of Sm2Fe17C2.5 at room temperature is 15±0.5 T.
TL;DR: In this article, the spontaneous magnetization of ferromagnetic clusters of various structures and sizes has been modeled with the Heisenberg model, and a self-consistent spinwave-spectrum is found by direct diagonalization of the equation of motion of S+.
TL;DR: In this article, the divalent and tetravalent ions are ordered to a considerable extent in the whole compositional range, and the ferromagnetic superexchange interactions between neighboring Mn 4+ and Ni 2+ ions are estimated to be 26 K in magnitude.
Abstract: Magnetization measurement and 55 Mn NMR study on a ferromagnet system La(Ni 2+ 1- x Mg x 2+ ) 0.5 Mn 0.5 4+ O 3 are made. The divalent and the tetravalent ions are found to be ordered to a considerable extent in the whole compositional range, and the ferromagnetic superexchange interactions between neighboring Mn 4+ and Ni 2+ ions are estimated to be 26 K in magnitude. 55 Mn NMR signals are observed for samples with x ≤0.6 in a frequency range between 270 and 310 MHz. The spectra composed of several equidistantly separated peaks can be successfully interpreted as each peak being the signal from Mn 4+ surrounded by a specific number of Ni 2+ ions. The hyperfine magnetic field at 55 Mn supertransferred from a neighboring Ni 2+ ion is determined to be 6.3 kOe, and the field originating from the own 3d magnetic moment of Mn 4+ ion is estimated to be -295 kOe, being a typical value for Mn 4+ ions in oxides.
TL;DR: In this article, a broad band dielectric spectroscopy (10 mHz-1 GHz) at temperatures covering the ferroelectric, paraelectric and molten phases as well as the glassy and rubbery states was investigated.
Abstract: Ferroelectric copolymers of vinylidene fluoride with trifluoroethylene and tetrafluoroethylene have been investigated by means of broad band dielectric spectroscopy (10 mHz-1 GHz) at temperatures covering the ferroelectric, paraelectric and molten phases as well as the glassy and rubbery states. The low-temperature relaxation spectra near Tg (∼ -40°C) consist of two processes; a WLF-type segmental mode and an Arrhenius type local mode. These processes are unified near room temperature to be transferred continuously to the high-temperature process. After showing a peak at the Curie point Tc (70–140°C), the relaxation strength decreases gradually in the paraelectric phase until the melting point Tm (∼ 150°C) is reached, where it decreases rapidly. It is found that the relaxation time in the molten phase lies on the Arrhenius line extended from the low-temperature local mode process. This implies that related molecular motions arise from a common elementary process. Departure from this Arrhenius lin...
TL;DR: In this article, KTiOAsO4 was grown by the high temperature solution method and their optical and ionic conductivity properties evaluated, including the band edge and IR cutoff were 370 and 4850 nm, respectively.
Abstract: Crystals of KTiOAsO4 were grown by the high temperature solution method and their optical and ionic conductivity properties evaluated. The band edge and IR cutoff were 370 and 4850 nm, respectively. A domain structure prevented efficient frequency conversion in as‐grown crystals. The ionic conductivity at 22 °C and 120 kHz was 1.5×10−8, 7.3×10−9, and 1.7×10−6 S/cm for the [100], [010], and [001], respectively. The alleged ferroelectric Curie temperature was 852 ±2 °C.
TL;DR: In this paper, a new hyperfine field distribution analysis method was proposed for room temperature Mossbauer spectra of 15 splat-quenched Fe−Ni alloys in the composition range of 5-70 at%Fe and low and high temperature spectra for an Fe65Ni35 Invar sample.
TL;DR: In this paper, the phase transition behavior in the systems of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) and 0.99Pb1-yLa2y/3TiO 3-0.01MnO2 (PLT) relaxor ferroelectrics has been investigated to explore the nature of diffused phase transitions in these materials.
Abstract: The phase transition behavior in the systems of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) and 0.99Pb1-yLa2y/3TiO3-0.01MnO2 (PLT) relaxor ferroelectrics has been investigated to explore the nature of diffused phase transitions (DPT) in these materials. All the dielectric constant (e)-temperature (T) characteristics for these materials above the Curie point have been found to be described by the equation (1/e-1/em)1/n=(T-Tm)/C', where em is the maximum dielectric constant of a material, Tm is the temperature giving em, and n and C' are constants changing with composition. In the system PMN-PT, the value of n was found to change continuously from 1.0 for PT to 2.0 for PMN without any irregularity. The value of n for the materials of the system PLT also shows a similar variation with La content, and moreover, two C' versus Tm plots obtained for the two systems PMN-PT and PLT show substantially the same behavior. The nature of DPT is considered to be closely connected with compositional and structural variations, which determine the spatial size and morphology of ferroelectric domains below the Curie point.
TL;DR: In this paper, the intrinsic magnetic properties of the interstitial Th2Zn17-type nitrides were investigated over the whole concentration range for Sm2(Fe1−xCox)17.
TL;DR: The results suggest that for temperatures Tg, Tc, C the system behaves like a two-dimensional Heisenberg magnet.
Abstract: The response of magnetization to the application of a magnetic field has been measured above the Curie temperature ${\mathit{T}}_{\mathit{C}}$ in epitaxial Co films on Cu(100). Magnetic domain images have been acquired up to ${\mathit{T}}_{\mathit{C}}$. The results suggest that for temperatures Tg${\mathit{T}}_{\mathit{C}}$ the system behaves like a two-dimensional Heisenberg magnet.
TL;DR: In this article, the magnetic susceptibilities of YCo 2 and LuCo 2 exchange-enhanced paramagnets, at high temperatures, obey a Curie-Weiss behaviour, and the effective moments per cobalt atoms determined from the Curie constants are close to that of Co 2+ ion.
TL;DR: All are weak ferromagnets with a nearly-full 3d subband, although when Z=N, the magnetic moment of 38.1 μg is very close to the fully saturated value of 39.4 μg.
Abstract: Measured magnetization and 57 Fe hyperfine fields at T∼0 K for Y 2 Fe 17 and Y 2 Fe 17 Z 3-δ , with Z=H, C, or N and δ∼0. 5, are analyzed to determine the influence of the interstitial atoms on the 3d magnetism. All are weak ferromagnets with a nearly-full 3d subband, although when Z=N, the magnetic moment of 38.1 μg is very close to the fully saturated value of 39.4 μg
TL;DR: The thermal stability, structural and magnetic properties of Sm 2 (Fe 1− x M x ) 17 N y nitrides (M = Co, Ni, Al, Ti and V) have been investigated.
TL;DR: In this paper, the substitution of Fe2+ ion with Co2+ and Mn2+ ions causes a decrease of the spontaneous moment μ and the Curie temperature Tc of X-type hexaferrites.
Abstract: Polycrystalline samples of X‐type Ba2Me2Fe28O46 (Me2‐X, Me=Fe, Co, and Mn) hexagonal ferrite have been prepared by the classic ceramic method. Low‐temperature magnetic properties, Curie temperatures, and distribution of divalent cations were studied. The substitution of Fe2+ ions with Co2+ and Mn2+ ions causes a decrease of the spontaneous moment μ and the Curie temperature Tc of X‐type hexaferrites. The lower μ and Tc of Co2‐X hexaferrite originate from the smaller magnetic moment of Co2+ ions. In the case of Mn2‐X, the lower μ may be due to the valence state of Mn and the lower Tc may be caused by the fact that the space distribution of 3d electrons of Mn is different from that of Fe. In the Co2‐X and Fe2‐X compounds the Co2+ and Fe2+ ions enter the octahedral sites of spinel S blocks.