Curie Constant Research Articles

Investigation on Thermodynamic and Paramagnetic Centres in Gd-Doped LiGa5O8 Inverse-Spinel-Structure

The present work reports the steady 3+ state of Gd in the LiGa5O8 matrix using the combustion route without a further calcining treatment. The as-prepared combustion products were well characterized by x-ray diffraction, and scanning electron microscope measurements. The electron paramagnetic resonance (EPR) spectrum of this system exhibited various resonance signals between g = 2.0 and 6.05. The EPR parameters of the system at 300 K and 110 K were calculated and compared. From the EPR data, various EPR parameters such as the number of spins, Gibbs free energy, magnetic susceptibility, empirical Curie constant, empirical Curie temperature, effective magnetic moment and zero-field splitting values are calculated and compared.

Magnetocaloric behavior of chromium doped Pr0.5Sr0.5MnO3 system

The magnetocaloric behavior of chromium doped Pr0.5Sr0.5MnO3 manganite system has been studied by synthesizing a series of samples using the citrate sol–gel route. The samples were characterized structurally by XRD and found to be crystallized in orthorhombic structure with Pnma space group. A systematic investigation of magnetization over a temperature range 80–300 K was carried out mainly to understand their magnetic behavior and the transition temperatures are found to decrease with increase in chromium concentration. This may be due to change in Mn3+ and Mn4+ ratio. Further, from the fittings (using a theoretical model) of M-T data at 500 Oestered magnetic field, curie constant has been calculated. It has been observed that due to chromium doping ferromagnetic phases were induced in the charge ordered system and this gave rise to interesting phenomena.

Magnetic ground state, field-induced transitions, electronic structure, and optical band gap of the frustrated antiferromagnet GeCo2O4

Systematic studies of magnetic ordering, magnetic-field-induced transitions, electronic structure, and optical properties of the frustrated spinel ${\mathrm{GeCo}}_{2}{\mathrm{O}}_{4}$ (GCO) are reported. Our results reveal that GCO orders antiferromagnetically (AFM) at ${T}_{\mathrm{N}}=20.4$ K but with significant short-range ferromagnetic (FM) order up to $T$ $\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}{T}_{\mathrm{N}}$. The paramagnetic susceptibility ($\ensuremath{\chi}$) fits the modified Curie--Weiss law, $\ensuremath{\chi}={\ensuremath{\chi}}_{\mathrm{o}}$ + $C$/($T\ensuremath{-}$ $\ensuremath{\theta}$), with $\ensuremath{\theta}=+51$ K for 100 K $T800$ K. The fit to high-temperature-series expansion of $\ensuremath{\chi}(T$) yields J${}_{1}$/${\mathrm{k}}_{\mathrm{B}}=14.7$ K as the dominant FM exchange coupling for the pyrochlore lattice of ${\mathrm{Co}}^{2+}$ spins consisting of alternate planes of Kagom\'e (KGM) and Triangular (TRI) spins lying perpendicular to [111] direction. From the analysis of the M-H plots at 2 K and published results, three critical fields are identified: ${H}_{d}\ensuremath{\sim}11$ kOe due to AFM domains, ${H}_{C1}\ensuremath{\approx}$ 44 kOe related to spin-flips and FM ordering of the TRI spins, and ${H}_{C2}\ensuremath{\approx}97$ kOe related to FM ordering of the KGM spins. For $H$ g ${H}_{C2}$, GCO is a forced ferromagnet with some canting of the spins. Magnetic field dependence of ${T}_{\mathrm{N}}$ follows the relation ${T}_{\mathrm{N}}(H)={T}_{\mathrm{N}}$(0)--${D}_{1}{H}^{2}$ valid for antiferromagnets with ${D}_{1}=6.63\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ K/${\mathrm{Oe}}^{2}$. This magnitude of T${}_{\mathrm{N}}$(H) along with the temperature dependence of H${}_{d}$, H${}_{C1}$, and H${}_{C2}$ are used to construct the H-T phase diagram. From the magnitudes of the Curie constant ($C$) and the saturation magnetization at 2 K it is shown that ${\mathrm{Co}}^{2+}$ ions in GCO have the ground state with effective spin $S$ = 1/2. High resolution x-ray photoelectron spectra of 2p and 3d orbitals of Co and Ge confirm the divalent and tetravalent electronic states of Co and Ge, respectively, in GCO. The energy band gap (${E}_{g}=3.28$ eV) evaluated using DFT+U calculations is in good agreement with the experimental results (${E}_{g}=3.16$ eV) obtained from the diffuse reflectance spectroscopy.

Composition dependence of magnetic properties in the mixed magnet Co1−xNixCl2·H2O

Abstract Effects of disorder, frustration and low dimensional character occur in mixed magnetic Co1−xNixCl2·H2O, examined by dc magnetization and susceptibility measurements across the composition range. The pure components are quasi-one-dimensional antiferromagnets ordering at 15.0 K (Co) and 5.65 K (Ni), with susceptibility maxima at 16.2 and 8.4 K respectively; a spin glass transition also appears in the cobalt system near 8 K. In each compound weaker antiferromagnetic interchain exchange interactions supplement dominant ferromagnetic exchange along MCl2MCl2M… chemical and structural chains. High temperature magnetic susceptibilities are analyzed to yield Curie and Weiss constants in χM = C/(T − θ). Regular but not mean-field composition dependences appear for C and θ. The former is not linear and the latter displays a minimum near x = 0.30. Notable is a susceptibility maxima varying in location only weakly from x = 0.10 to x = 0.70, decreasing markedly only for higher x. Magnetization isotherms evolve regularly as x varies, with systematic composition dependences of a metamagnetic transition field and hysteresis through x = 0.70. A qualitative change in the isotherms occurs for x = 0.90, but substantial curvature still appears with smaller but definite hysteresis. A thermoremanent magnetization is seen in all mixtures, and is largest for the composition extremes. Thus, nonequilibrium magnetic behavior characteristic of the cobalt component, in contrast to the more conventional nickel component, occurs even when the latter is present in strong majority.

Magnetic properties of Fe-doped CuAlO2 and role of impurities

The delafossite CuAlO2 is a rare p-type semiconductor with potential applications as a thermoelectric and as a dilute magnetic semiconductor when doped with transition metal ions. Reported here are results from our investigations of CuAl1-xFexO2 (x = 0, 0.01, 0.05, and 0.1) with a focus on the x-dependence of structural and magnetic properties, and role of impurities. The samples prepared by the solid-state reaction at 1,100°C were characterized by X-ray diffraction (XRD), energy dispersive (X-ray) spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The magnetic results show that the Curie constant (C), low temperature magnetization (M) and the lattice constants scale with x. High resolution M-H loop measurements at 300 K and 10 K show negligible coercivity HC at 10 K but HC ∼ 100 Oe at 300K. These results suggest the presence of minute quantities of hematite (α-Fe2O3) that are not detected in our XRD and XPS. The role of impurities on the published results in this system is discussed.

Rational Design and Synthesis of a Chiral Lanthanide-Radical Single-Chain Magnet.

By the reaction of an enantiopure nitronyl nitroxide radical, 2-((1 R)-(-)-myrtenal)-4,4,5,5-tetramethylimidazolin-1-oxyl-3-oxide), abbreviated as (1 R)-(-)-myrtenal-NIT, and Dy(hfac)3·2H2O (hfac = hexafluoroacetylacetonate), we successfully obtained a homochiral DyIII-radical chain compound [Dy(hfac)3(1 R)-(-)-myrtenal-NIT] n (1) with full characterization. 1 crystallizes in the chiral P21 space group and exhibits slow magnetization relaxation, holding an effective energy barrier (Δτ/ kB) of 64.6 K (44.9 cm-1) and an attempt time τ0 of 1.0 × 10-7 s. The correlation energy (Δξ/ kB) of this chain is 10.4 K (7.2 cm-1), and the effective Curie constant is 2.8 cm3·K·mol-1. Additionally, 1 exhibits temperature-dependent hysteresis loops below 4 K, with a maximum coercive field of 0.51 T at 2 K.

Electronic state and concentration of Fe3+ in CuAl1−Fe O2 determined by magnetic measurements

Abstract CuAlO2 is among several ternary delafossites in which the electronic bandgap is less than the optical bandgap due to Laporte selection rules. Because alloying is expected to provide band engineering in delafossites, we are investigating Fe-doped CuAlO2. Here, results from the detailed magnetic characterization of the CuAl1−xFexO2 (x = 0.0, 0.01, 0.05, and 0.1) samples, prepared by a solid-state reaction of Cu2O, Al2O3, and Fe2O3, at 1100 °C, are reported. X-ray diffraction (XRD) of the powder samples showed an expansion of the rhombohedral unit cell with increasing x showing that the larger Fe3+ (r = 0.645 A) is replacing the smaller Al3+ion (r = 0.535 A). The analysis of magnetization (M) vs. temperature (T, from 2 to 300 K) data in terms of the Curie-Weiss law: M = CH/(T − θ) confirms Fe3+ as the electronic state of Fe with spin S = 5/2 (magnetic moment μ = 5.9 μB) as determined from the Curie constant, C; this analysis also yields a negative θ characteristic of an antiferromagnetic Fe3+–Fe3+ exchange coupling and magnitudes of x in good agreement with the nominal values. The isothermal M vs. H (up to H = 90 kOe) data analyzed in terms of modified Brillouin function involving H/(T − θ) support the results obtained from the M vs. T analysis. The small paramagnetism observed in undoped CuAlO2 is related to the presence of a few percent of CuAl2O4 impurity observed in XRD of the sample.

Effect of the Substitution Pattern (Peripheral vs Non-Peripheral) on the Spectroscopic, Electrochemical, and Magnetic Properties of Octahexylsulfanyl Copper Phthalocyanines.

In order to investigate the substitution position effect on the spectroscopic, electrochemical, and magnetic properties of copper phthalocyanines, a detailed structure-property analysis has been performed by examining two copper phthalocyanines that are octasubstituted by hexylsulfanyl chains respectively in the peripheral (Cu-P) and non-peripheral (Cu-NP) positions. Cu-NP showed a marked near-IR maximum absorption compared to Cu-P and, accordingly, a smaller HOMO-LUMO energy gap, calculated via the electrochemical results and simulations in the gas phase, as well as for Cu-NP from its crystallographic data. An electron-spin resonance (ESR) technique is used to extract the g values from the powder spectra that are taken at room temperature. The g values were determined to be g∥ = 2.160 and g⊥ = 2.045 for Cu-P and g∥ = 2.150 and g⊥ = 2.050 for Cu-NP. These values indicate that the paramagnetic copper center in both phthalocyanines has axial symmetry with a planar anisotropy ( g∥ > g⊥). The ESR spectra in solution could be obtained only for Cu-P. Curie law is used to fit the experimental data of the magnetic susceptibility versus temperature graphs, and the Curie constant ( C) and diamagnetic/temperature-independent paramagnetic (α) contributions are deduced as 0.37598 (0.39576) cm3·K/mol and -23 × 10-5 (25 × 10-5) cm3/mol respectively for Cu-P and Cu-NP. The room temperature magnetic moment value (1.70 μB) is close to the spin-only value (1.73 μB) for the peripheral complex, showing that there is no orbital contribution to μeff. In contrast, at room temperature, the value of the magnetic moment (1.77 μB) is above the spin-only value, showing an orbital contribution to the magnetic moment. Cu-NP's room temperature magnetic moment value is larger than the value for Cu-P, demonstrating that the orbital contribution to the magnetic moment depends upon the substituent position. The magnitudes of the effective magnetic moment values also support that both Cu-P and Cu-NP complexes have square-planar coordination. This result is consistent with the determined g values. The spin densities were determined experimentally, and the results suggest that the positions of the substituents affect these values (0.469 for Cu-P and 0.490 for Cu-NP).

Influence of Depolarizing Fields and Screening Effects on Phase Transitions in Ferroelectric Composites.

The temperature of the transition to the polar state in ferroelectric composites, representing spherical ferroelectric inclusions embedded in a dielectric matrix, under a depolarizing field effect is investigated. This temperature is determined both in the absence and presence of screening effects of the depolarizing field of the bound charges of spontaneous polarization at the inclusions surface. The absence case shows that the Curie point shift is determined by the ratio of the Curie constant of the ferroelectric inclusion to the permittivity of the matrix. Screening effects show that the transition temperature shift decreases through multiplying the value by a decreasing factor equal to the ratio of the screening length to the radius of the ferroelectric inclusion. Examples of the materials for the position of the Curie point on the temperature scale, largely determined by the tilting action of the depolarizing field and the compensating shielding effects, are given.

A Method for Studying the Magnetic Susceptibility of Colloidal Solutions in Ferrofluidic Cells

A technique for studying the magnetic susceptibility of colloidal solutions in a hermetically sealed glass volume (a ferrofluidic cell) is proposed. Experimental investigations have shown that Curie’s law holds in the temperature range of 283–323 K at which ferrofluidic cells are used. A further increase in the temperature of a colloidal solution in a ferrofluidic cell leads to an increase in the Curie constant C, which is due to the fact that the thermal motion of molecules destroys conglomerates with antiparallel magnetic moments of nanoparticles that have a binding energy of the order of kТ.

Nematic fluctuations in iron-based superconductors studied by resistivity change under uniaxial pressure

Antiferromagnetic, nematic and superconducting phases have been widely found in iron-based superconductors. The study on their relationships is thus crucial for understanding the low-energy physics and high-temperature superconductivity. The so-called nematic phase represents a spontaneous in-plane rotational symmetry breaking of the electronic states, which results in strong in-plane anisotropic properties. We have developed a uniaxial pressure device, which enables us to obtain nematic susceptibility by studying the resistivity change under uniaxial pressure at low temperature. In this paper, we brief two of our recent researches on nematic fluctuations in iron-based superconductors. The first research shows the presence of a nematic quantum critical point in BaFe2-xNixAs2, which exhibits several characteristics, including the zero mean-field nematic transition temperature x=0.11, broad hump feature in the nematic susceptibility in overdoped samples, strongest nematic susceptibility along the (100) direction at x=0.11, and the divergence of zero-temperature nematic susceptibility at x=0.11 for uniaxial pressure along both the (110) and (100) directions. We further study the nematic susceptibility in many other iron-based superconductors and find that the ordered moment at zero temperature linearly scales with nematic Curie constant, which is obtained from the Curie-Weiss-like temperature dependence of nematic susceptibility in these materials. Accordingly, we propose a universal phase diagram for iron-based superconductors, where superconductivity is achieved by suppressing the long-range antiferromagnetic order in a hypothetical parent compound though the enhancement of nematic fluctuations by doping, including both carrier doping and isovalent doping. Our results suggest that nematic fluctuations play a very important role in both the antiferromagnetism and superconductivity in iron-based superconductors.

Copper(II) complexes of picolinamide incorporating both tricyanomethanido and 2-(aminomethyl)pyridine moieties

Reaction of picolinamide (pca) with potassium tricyanomethanide (tcm) and copper(II) perchlorate in 1-propanol gave [Cu(pca)2(tcm)2] (1a and 1b) while addition of 2-(aminomethyl)pyridine (2-ampy) provided [Cu(pca)(2-ampy)(tcm)](ClO4) (2). These compounds have been characterized by IR, powder X-ray diffraction, single crystal X-ray diffraction, combustion analysis, and temperature-dependent magnetic susceptibility. Compound 1a crystallized in the monoclinic space group C2/c whereas 1b and 2 crystallized in the triclinic space group Pī. In 1a, the copper complexes stack alternately with semi-coordinated tcm ions creating layers, further stabilized by hydrogen bonding to neighboring layers. In 1b, the tcm ions are coordinated to complete the octahedral coordination sphere around the copper ions and form staggered layers parallel to the ab face diagonal. In 2, stacks of copper complexes form bilayers, held together by hydrogen bonding between tcm ions and amino groups, parallel to the a axis. Variable temperature magnetic susceptibility data were collected on 1 and 2 from 1.8–310 K. The data were fit to the Curie–Weiss law which showed no significant magnetic exchange as expected based upon the crystal structures [1 − Curie constant = 0.419(2) emu-K/mol-Oe, θ = −0.10(6)°; 2 – Curie constant = 0.438(1) emu-K/mol-Oe, θ = 0.05(3)°].

Research on electrostrictive effect of second-order phase transition ferroelectrics

ABSTRACTReversible electrostrictive effect in ferroelectrics of double-well free energy is modeled using the Devonshire theory. The idea is developed that in tetrogonal phase 90° turnings of dipoles from four poling axises, isoenergetic minima, perpendicular to electrical field to the direction of electrical field cause electrostriction. Numerical simulation results exhibit that the exchanging coupling coefficient between dipoles results in a butterfly shaped electrostriction loop. Influences of temperature and the two parameters of materials on shape of electrostriction loop are discussed, and an empirical experimental law, about magnitude of electrostriction with the Curie constant, is confirmed.

Unified Phase Diagram for Iron-Based Superconductors

High-temperature superconductivity is closely adjacent to a long-range antiferromagnet, which is called a parent compound. In cuprates, all parent compounds are alike and carrier doping leads to superconductivity, so a unified phase diagram can be drawn. However, the properties of parent compounds for iron-based superconductors show significant diversity and both carrier and isovalent dopings can cause superconductivity, which casts doubt on the idea that there exists a unified phase diagram for them. Here we show that the ordered moments in a variety of iron pnictides are inversely proportional to the effective Curie constants of their nematic susceptibility. This unexpected scaling behavior suggests that the magnetic ground states of iron pnictides can be achieved by tuning the strength of nematic fluctuations. Therefore, a unified phase diagram can be established where superconductivity emerges from a hypothetical parent compound with a large ordered moment but weak nematic fluctuations, which suggests that iron-based superconductors are strongly correlated electron systems.

Synthesis, structure and magnetic studies of lanthanide metal–organic frameworks (Ln–MOFs): Aqueous phase highly selective sensors for picric acid as well as the arsenic ion

A series of three lanthanide metal–organic frameworks (Ln–MOFs) consisting of a planar functionalized dicarboxylic acid was synthesized. The Ln–MOFs, with the composition [Ln3(PDC)3Cl3(H2O)]n [Ln = La (1), Nd (2) or Pr (3), PDCH2 = pyridine-2,6-dicarboxylic acid], were characterized employing spectral, time resolved fluorescence, magnetic, single crystal X-ray and PXRD analysis. X-ray crystallography confirms that the structure of the Ln–MOFs is constructed by trinuclear (Ln3) units and the deprotonated PDC2− ligand, which is simplified into a 3-c, uninodal net having the vab topology with the 10^3-point symbol. The variable temperature magnetic susceptibility data indicate that there are antiferromagnetic interactions between LnIII⋯LnIII ions in 2 and 3 with Curie constants of 5.917 (2) and 5.231 (3) cm3 K mol−1, Weiss constants −60.71 (2) and −48.43 (3) K, and zJ′ values −0.98 (2) and −0.31 (3) cm−1. The 3D polymers 1–3 are characterized as being highly selective, sensitive and discriminative dual chemosensors for picric acid (PA) and the arsenite (AsO33−) ion in aqueous medium. The sensing pathways were investigated by spectral titrations, time decay and DFT (B3LYP/def2–SVP) studies. The lowest detection limit has been discovered for the La analogue towards the sensing of both PA and AsO33− {or As(III)} ions with ∼0.22 and ∼1.46 ppb, respectively. Such MOFs exhibiting bifunctional sensing behaviour for an explosive (PA) as well as toxic ion, As(III), in the aqueous phase are disclosed as the first lanthanide 3D polymers with the lowest detection limit known so far for the said analytes.

Substitution effects on the bulk and surface properties of (Li,Ni)Mn2O4

Manganese oxides of spinel structure, LiMn2O4, Li1-x Ni x Mn2O4 (0.25 ≤ x≤ 0.75), and NiMn2O4, were studied by EDS, XRD, SEM, magnetic (M-H, M-T), and XPS measurements. The samples were synthesized by an ultrasound-assisted sol-gel method. EDS analysis showed good agreement with the formulations of the oxides. XRD and Rietveld refinement of X-ray data indicate that all samples crystallize in the Fd3m space group characteristic of the cubic spinel structure. The a-cell parameter ranges from a = 8.2276 A (x = 0) to a = 8.3980 A (x = 1). SEM results showed particle agglomerates ranging in size from 2.3 μm (x = 0) down to 0.8 μm (x = 1). Hysteresis magnetization vs. applied field curves in the 5–300K range was recorded. ZFC-FC measurements indicate the presence of two magnetic paramagnetic-ferrimagnetic transitions. The experimental Curie constant was found to vary from 5 to 7.1 cm3 K mol−1 for the range of compositions studied (0 ≤ x ≤ 1). XPS studies of these oxides revealed the presence of Ni2+, Mn3+, and Mn4+. The experimental Ni/Mn atomic ratios obtained by XPS were in good agreement with the nominal values. A linear relationship of the average oxidation state of Mn with Ni content was observed. The oxide’s cation distributions as a function of Ni content from x = 0 Li+[Mn3+Mn4+]O4 to x = 1 $$ {\mathrm{Ni}}_{0.35}^{2+}{\mathrm{Mn}}_{0.65}^{3+}\left[{\mathrm{Ni}}_{0.65}^{2+}\right.\left.{\mathrm{Mn}}_{1.35}^{3+}\right]{\mathrm{O}}_4 $$ were proposed.

Measurement of Magnetic Susceptibility and Curie Constants of Colloidal Solutions in Ferrofluid Cells by the Nuclear Magnetic Resonance Method

A new method is proposed for determining the magnetic susceptibility and Curie constants of various colloidal solutions in sealed glass volumes (ferrofluid cells) with an error of no more than 1.0% even with a small thickness of the layer of solution. It is shown that intensive stirring of the solution is necessary for excluding changes in the Curie constants as the cell temperature increases.

Low temperature physical properties of Co-35Ni-20Cr-10Mo alloy MP35N®

Multiphase Co-35Ni-20Cr-10Mo alloy MP35N® is a high strength alloy with excellent corrosion resistance. Its applications span chemical, medical, and food processing industries. Thanks to its high modulus and high strength, it found applications in reinforcement of ultra-high field pulsed magnets. Recently, it has also been considered for reinforcement in superconducting wires used in ultra-high field superconducting magnets. For these applications, accurate measurement of its physical properties at cryogenic temperatures is very important. In this paper, physical properties including electrical resistivity, specific heat, thermal conductivity, and magnetization of as-received and aged samples are measured from 2 to 300K. The electrical resistivity of the aged sample is slightly higher than the as-received sample, both showing a weak linear temperature dependence in the entire range of 2–300K. The measured specific heat Cp of 430J/kg-K at 295K agrees with a theoretical prediction, but is significantly smaller than the values in the literature. The thermal conductivity between 2 and 300K is in good agreement with the literature which is only available above 77K. Magnetic property of MP35N® changes significantly with aging. The as-received sample exhibits Curie paramagnetism with a Curie constant C=0.175K. While the aged sample contains small amounts of a ferromagnetic phase even at room temperature. The measured MP35N® properties will be useful for the engineering design of pulsed magnets and superconducting magnets using MP35N® as reinforcement.

Magnetic investigations of phase transitions, exchange interactions, and magnetic ground state in nanosheets of β-Co(OH)2

Detailed investigations of the magnetic properties of the layered system β-Co(OH)2 are presented. X-ray diffraction and scanning electron microscopy of the sample show it to consist of hexagonal nanosheets with thickness ≈30 nm and width ~100 nm–200 nm. Analysis of its measured magnetization (M) as a function of temperature (T = 2 K to 300 K) and magnetic field (H up to 90 kOe) yields a Neel temperature TN = 9.2 K. This lower TN = 9.2 K, compared to TN = 11.6 K reported for bulk β-Co(OH)2, is due to finite-size effects. Analysis of the data for T > TN shows that the M versus T data does not quite fit the Curie–Weiss law since both the Curie constant C and Weiss temperature θ have noticeable temperature dependence. This temperature dependence is interpreted to be due to the effect of spin–orbit coupling, yielding a low-temperature effective spin S = 1/2 ground state with magnetic moment µ = 4.745 µB and g = 5.479. For T < TN, M versus H data show two transitions, first at HC1 ≃ 15 kOe and second at HC2 ≃ 32 kOe. The transition at HC1 is a spin-flop transition and HC2 is due to forced alignment of the spins yielding saturation magnetization MS = 160 emu g−1 at 2 K, in agreement with the calculated MS = 163 emu g−1 for the complete alignment of the spins at T = 0 K for the spin S = 1/2 ground state with g = 5.479. The fitting of the M versus T data for T > TN to the high temperature series for S = 1/2 XY model yields the in-plane ferromagnetic exchange constant J1/kB = (1.8 ± 0.2) K for Co2+ ions, with the interplane exchange constant J2/kB ≃ −0.2 K determined from the magnitude of TN. The temperature dependence of HC1 and HC2 is presented and discussed.

Nondestructively measuring the remanent polarization of PZT 95/5 ceramics at room temperature

AbstractPZT95/5 ferroelectric ceramics are widely utilized in pulsed power devices and the remanent polarization Pr of poled PZT95/5 can characterize the shock‐driven energy density. However, this remanent polarization is difficult to be measured nondestructively. In this article, a series of pyroelectric tests of poled PZT95/5 ceramics were conducted near room temperature, from 25°C to 20°C. A linear relation between Pr and pyroelectric coefficient p was found, that is, Pr=1190.5(K)×p, which provides an effective way to nondestructively estimate the value of Pr of the poled PZT95/5 ceramics by measuring the pyroelectric coefficient p at room temperature. According to Devonshire's phenomenological theory, this result could be explained by a modified equation: , where ɛr represents the relative dielectric constant, C represents the Curie constant, and α (equals to 0.52 for PZT95/5 ceramics) represents a modification factor for ceramics, respectively.