Contribution of Co3+ ions to the high-temperature magnetic and electrical properties of GdCoO3

The temperature dependence of the static magnetization of polycrystalline rare-earth cobaltite GdCoO₃ is measured in the temperature range 2?C800 K. The magnetic behaviors of GdCoO₃ and Gd³⁺ are found to be different at temperatures above room temperature, which is caused by the appearance of a contribution from Co³⁺ ions at high temperatures. The temperature dependence of the magnetic susceptibility of GdCoO₃ is determined by the magnetization of rare-earth gadolinium ions and the additional paramagnetic contribution induced by the thermally excited magnetic terms of Co³⁺ ions. The LDA + GTB method is used to calculate the electronic structure of GdCoO₃ in the temperature range 0?C300 K with allowance for strong electron correlations. The energy spectrum of GdCoO₃ is found to have intragap states that decrease the dielectric gap width with increasing temperature.     

Electronic structure,magnetic properties,and mechanism of the insulator–metal transition in LaCoO<Subscript>3</Subscript> taking into account strong electron correlations

The electronic structure of LaCoO₃ at finite temperatures is calculated using the LDA+GTB method taking into account strong electron correlations and possible spin crossover upon an increase in temperature. Gap states revealed in the energy spectrum of LaCoO₃ reduce the dielectric gap width upon heating; this allowed us to describe the insulator-metal transition observed in this compound at T = 500–600 K. The temperature dependence of the magnetic susceptibility with a peak at T ≈ 100 K is explained by the Curie contribution from thermally excited energy levels of the Co³⁺ ion. At high temperatures, the Pauli contribution from a band electron is added and the total magnetization of LaCoO₃ is considered as the sum M _tot = M _loc + M _band. The second term describes the band contribution appearing as a result of the insulator-metal transition and facilitating the emergence of a high-temperature anomaly in the magnetic susceptibility of LaCoO₃.     

The energy gap of the high Tc superconductor La1.85Sr0.15CuO4

We have measured the energy gap of a polycrystalline sample of La_1.85Sr_0.15CuO₄ using far-infrared reflectance. The sample was prepared by sintering and has a superconducting transition at 36 ±1 K (mid point of a 2K wide region) both in resistance and magnetic susceptibility. The Meissner effect was incomplete and there was considerable absorption below the gap frequency in the superconducting state. The change in far infrared absorption on going to the superconducting state was fitted to the theory of Mattis and Bardeen, yielding an energy gap of (3.2 ± 0.3) kT_c withT_c= 36 K     

Faraday rotation in single crystal erbium iron garnet

Measurements of the Faraday rotation of ErIG, Er₃Fe₅O₁₂, have been performed in the 4.2–300 K temperature range in magnetic field up to 20 kOe applied along the [111] direction and at 1.15 μm wavelength. The results are analysed under the assumption that the contribution of the Fe³⁺ ions to the total Faraday rotation is the same as that of YIG, Y₃Fe₅O₁₂. The temperature and field dependences of the contribution of the Er³⁺ ions are deduced. Both magnetic and electric dipole contributions of the Er³⁺ ions are calculated; the electric dipole coefficient C_e is found to present a linear temperature dependence between 30–300 K. The temperature dependence of the Faraday rotation susceptibility differs strongly from that of the magnetic susceptibility.     

Low temperature heat capacity and magnetic study of the Al80Mn20 icosahedral alloy

Low temperature heat capacity and magnetization measurements are reported for the Al₈₀Mn₂₀ alloy in the quasicrystalline icosahedral phase. The heat capacity, which was measured for temperatures ranging from 0.5 to 5.0 K and magnetic fields up to 11.7 kOe, shows a broad magnetic contribution around 1.0 K. The linear electronic contribution does not indicate an anomalously high density-of-states at the Fermi energy as predicted theoretically for quasicrystalline systems. The d.c. magnetization, which was measured from 2.0 to 300 K and with magnetic fields up to 50 kOe, indicates an effective number of one 11 μ_B localized magnetic moment for approximately every 100 Mn atoms. The low field susceptibility follows the Curie-Weiss law for temperatures ≧ 10 K, while a spin-glass-like ordering is observed at low temperatures.     

Magnetism and electronic structure of the intermetallic compound Ce5CuBi3

We have studied the electronic structure as well as magnetic, electronic transport and thermodynamic properties of the intermetallic compound Ce₅CuBi₃. It was found that Ce₅CuBi₃ undergoes three successive phase transitions at 25?K, 13.7?K and 3.5?K. We attribute the multiple magnetic phase transition to be associated with the two non-equivalent magnetic sublattices of the magnetic Ce ions. The investigated compound is characterized by an enhanced ratio C_p /T at 2?K, which may be interpreted as being due to the nearness of the 4f-level to the Fermi level and some contribution of magnon excitation. The core-level photoemission spectra indicate that Ce ions in Ce₅CuBi₃ are very close to trivalent which is consistent with the magnetic susceptibility data. The calculated band structures using the scalar-relativistic linear muffin-tin orbital method in the atomic sphere approximation and the all-electron full potential linear augmented plane wave plus local orbitals method have been performed for the non-magnetic ground state and as well as for collinear ferromagnetic and ferrimagnetic spin alignments. The largest stabilization energy is found in the case of a ferromagnetic structure. The calculated moments on the two sites of the Ce atoms are in agreement with the experimental value (0.93?μ _B /Ce). The calculations predict that the studied compound has a pseudogap in the DOS curve. Analysis of the partial DOS suggests some differences in hybridization strengths between the Ce-Bi and Ce-Cu orbitals.     

Mössbauer hyperfine interactions in natural wolframites

Powdered samples of Indian Natural Wolframites, (Fe_xMn_1?x) WO₄ with x=0.95 to 0.41, obtained from seven different locations of two quartz-wolframite deposits of Degana and Sirohi in Rajasthan, have been investigated by Mössbauer spectroscopy down to 20K and magnetic susceptibility down to 77K. The Mössbauer spectra from 300K to 30K clearly indicate multiple sites which is at variance with the reported work. Below 50K a weak magnetic interaction with H_int～45Koe is observed. The spectra above transition temperature are resolved in three doublets and explained on the basis of reported crystal structure. The values of isomer shift, quadrupole splitting and magnetic hyperfine field have been attributed to high spin ferrous ions with octahedral symmetry. Relatively small value of Q.S. (～1.5 mm/sec. at 300K) indicate a strong contribution of the lattice term to the electric field gradient.     

Synthesis,structure and magnetic properties of layered manganate Sr4Mn3−xCrxO10 (x=0, 0.2)

The manganates Sr₄Mn_3−xCr_xO₁₀ (x=0 and 0.2) have been synthesized by solid state reaction. Powder X-ray diffraction analysis shows orthorhombic symmetry with space group Cmca for both compounds. The magnetic susceptibility measurements show an antiferromagnetic transition at 192 and 176 K for x=0 and 0.2, respectively. The magnetic susceptibility data were estimated using a model based on spin exchange antiferromagnetic interactions in isolated (Mn⁴⁺) trimer; a paramagnetic contribution due to the chromium ions was added in the case of Cr-doped materials.     

Antiferromagnetic resonance and high magnetic field properties of NaNiO2

Magnetisation measurements up to 23 T and submillimeter wave ESR in the frequency region 48-380 GHz have been performed on NaNiO₂ powders at low temperature. Also typical spectra above the Néel temperature are shown. At 4 K the magnetisation shows a spin-flop transition at 1.8 T and saturation at 10 T. /Ni confirms the low spin state of the Ni³⁺ ions. The susceptibility exhibits a maximum at K with and K. NaNiO₂ is an A-type antiferromagnet: we derive K and K for the interactions between Ni ions within and between adjacent layers, respectively. The AFMR spectra yield an energy gap of 52.5 GHz, in agreement with the spin-flop value derived from the magnetisation. The anisotropy of the g factor observed at 100 K with can be attributed to the Jahn-Teller effect for Ni³⁺ ions in the low spin state, which stabilises the occupation. We finally comment on the isomorphic controversial Li_1-xNi_1+xO₂ compound. Received 9 March 2000 and Received in final form 13 July 2000.     

Thermodynamic and magnetic properties of LaSn3

Thermal expansion coefficient between 77 and 900K, isothermal compressibility in the 0–80 Kbar pressure range, magnetic susceptibility between 77 and 1300 K and heat capacity at constant pressure in the 20–300 K temperature range were determined for the LaSn₃ compound. From the experimental data, the specific heat at constant volume was calculated and the thermal dependence of the Debye's parameter θ_D was obtained. The electron contribution to the heat capacity was also determined from the high temperature data. The magnetic properties confirm that there is no evidence of the existence of a magnetic moment localized on La atoms, in contrast with a previous report and in agreement with the general assumptions. A little anomaly found in the expansion coefficient, in the isothermal compressibility and in the specific heat is discussed in terms of a lattice order-disorder phenomenon.     

Magnetic hyperfine interactions in GdAl3

We have studied the magnetic hyperfine interactions in GdAl₃ using¹⁵⁵Gd Mössbauer spectroscopy between the temperatures of 4K and 90K. Previous studies on GdAl₃ have shown that antiferromagnetic ordering occurs at 18K, and that a fit of the susceptibility to 1/(T-θ_p) yields a θ_p value of ?89K. The large ratio of θ_p to T_N is indicative of magnetic frustration between competing ferro-and antiferromagnetic interactions, which may be due to a combination of the oscillatory nature of the RKKY interaction and the geometry of the hexagonal lattice. Our studies show that the saturation magnetic hyperfine field at the Gd site is ?24.0 T, with the moments lying in the basal plane. The efg at the gadolinium site is 2.55(1)×10¹⁷V cm^?2 which is considerably larger than the value predicted by a point charge calculation. This difference may indicate that there is a conduction electron contribution. A helical magnetic structure has been calculated from RKKY theory.     

Anti-ferromagnetic ordering and crystal electric field in Ce:GSAG and Ce:LLGG garnets

The magnetic susceptibility of Ce:Gd₃Sc₃Al₃O₁₂ (Ce:GSAG) and Ce:La₃Lu₂Ga₃O₁₂ (Ce:LLGG) has been studied in the temperature range from 15 to 293 K. Both the Ce-doped garnets Ce:GSAG and Ce:LLGG show anti-ferromagnetic ordering at 18 and 27 K, respectively. Crystal electric field split energy levels have been used to calculate the magnetic susceptibility following Van Vleck's model. The calculated susceptibility values reasonably agree with the experimental susceptibility data of Ce:LLGG but differ for that of Ce:GSAG system. Contribution from long-range ordering between Ce and Gd ions for anomaly in Ce:GSAG system is speculated.     

Delocalization of the Ce 4f shell in amorphous Ce75.5Co24.5

The amorphous alloy Ce_75.5Co_24.5 prepared by melt spinning has been studied through measurements of the magnetic susceptibility, magnetization, electrical resistivity, thermoelectric power and specific heat. The results are interpreted in terms of a homogeneous intermediate valence state of the Ce ions. This is inferred from a temperature-independent magnetic susceptibility at low temperature and the absence of magnetic ordering, a large linear term in the specific heat, and aT ² dependence of the electrical resistivity at low temperature followed by a steep increase with temperature up to 50 K. At this temperature, the thermoelectric power displays a maximum. The intrinsic properties are partially obscured at low temperatures by a contribution from roughly a few percent of magnetic impurities, presumably Ce³⁺ ions. They manifest themselves by an increase of the susceptibility towards low temperatures and by a broad Schottky-like contribution to the specific heat resulting from the excitation of magnetic clusters.Dedicated to Prof. Dr. S. Methfessel on the occasion of his 60th birthday     

稀磁半导体Hg0.89Mn0.11Te磁化强度及磁化率的研究

利用MPMS-7(magnetic property measurement system)型超导量子磁强计对垂直布里奇曼法生长的Hg_0.89Mn_0.11Te晶片磁化强度变化规律进行了测量.试验采用了两种不同的外场和冷却条件.首先在5 K恒温下，-5200到5200 kA/m范围内改变磁场强度进行了测定.然后维持800 kA/m恒定磁场，分别在有场冷却和无场冷却条件下，从5到300 K范围内改变温度，研究了变温条件下的磁化特性.并采用分子场近似模型，用类布里渊函数，最小二乘法对磁化强度随磁场强度变化的实验结果进行拟合和分析，结果表明，Mn²⁺离子之间存在反铁磁相互作用.磁化率和温度关系分析表明：在测试范围内Hg_0.89Mn_0.11Te是单一的顺磁相，在高温区磁化率和温度服从居里-万斯定律，呈线性关系，低于40 K时，磁化率和温度的关系偏离居里-万斯定律，表现出顺磁增强现象. 关键词： 0.89Mn_0.11Te')" href="#">Hg_0.89Mn_0.11Te 磁化强度 磁化率 类布里渊函数     

Structural anomalies associated with the electronic and spin transitions in LnCoO<Subscript>3</Subscript>

A powder X-ray diffraction study, combined with magnetic susceptibility and electric transport measurements, was performed on a series of LnCoO₃ perovskites (Ln = Y, Dy, Gd, Sm, Nd, Pr and La) over a temperature range 100–1000 K. A non-standard temperature dependence of the observed thermal expansion was modelled as a sum of three contributions: (1) weighted sum of lattice expansions of the cobaltite in the diamagnetic low spin state and in the intermediate (IS) or high (HS) spin state. (2) An anomalous expansion due to the increasing population of excited (IS or HS) states of Co³⁺ ions over the course of the diamagnetic-paramagnetic transition. (3) An anomalous expansion due to excitations of Co³⁺ ions to another paramagnetic state accompanied by an insulator-metal transition. The anomalous expansion is governed by parameters that are found to vary linearly with the Ln ionic radius. In the case of the first magnetic transition it is the energy splitting E between the ground low spin state and the excited state, presumably the intermediate spin state. The energy splitting E, determined by a fit to magnetic susceptibility, decreases with temperature. The values of E determined for LaCoO₃ and YCoO₃ at T=0 K are 164 K and 2875 K respectively, which fall to zero at T=230 K for LaCoO₃ and 860 K for YCoO₃. The second anomalous expansion connected with a simultaneous magnetic and insulator-metal transition is characterized by its center at T=535 K for LaCoO₃ and 800 K for YCoO₃. The change of the unit cell volume during each transition is independent of the Ln cation and is about 1% in both cases.     

The influence of imperfection of the crystal lattice on the electrokinetic and magnetic properties of disordered titanium monoxide

The conductivity and magnetic susceptibility of disordered titanium monoxide TiO_y (0.920≤y≤1.262) containing vacancies in titanium and oxygen sublattices are investigated. For TiO_y monoxides with an oxygen content y≤1.069, the temperature dependences of the conductivity are described by the Bloch-Grüneisen function at a Debye temperature ranging from 400 to 480 K and the temperature dependences of the magnetic susceptibility are characterized by the contribution from the Pauli paramagnetism due to conduction electrons. The behavior of the conductivity and magnetic susceptibility of TiO_y monoxides with an oxygen content y≥1.087 is characteristic of narrow-gap semiconductors with nondegenerate charge carriers governed by the Boltzmann statistics. The band gap ΔE between the valence and conduction bands of TiO_y monoxides with y≥1.087 falls in the range 0.06–0.17 eV.     

Matrix embedded cobalt-carbon nano-cluster magnets: behavior as room temperature single domain magnets

A new type of Co-C nanoparticles is synthesized from CH₂Cl₂ solution of Co₄(CO)_{1 2} by heating up to 210 ^°C in a closed vessel. Transmission electron microscope (TEM) and electron energy loss spectroscopy (EELS) observation show that the particles are embedded in amorphous carbon and their average size is 12 nm. The radial structure function obtained from the extended X-ray absorption fine structure (EXAFS) of the Co K-edge absorption of the Co-C nanoparticles provides a Co-C average distance of 2.08 Å and the Co-Co distances of 3.18 Å and 3.9 (±0.2) Å. The particles exhibit the magnetic hysteresis curve with a coercive force of 200 Oe at 20 K and 260 Oe at 300 K. The temperature dependence of the magnetic susceptibility measured under zero-field cooling and 10 Oe field cooling conditions exhibits the behavior characteristic of a set of single magnetic domain nanomagnets in an amorphous carbon matrix.     

SrCoxZrxFe12−2xO19 and SrNixZrxFe12−2xO19 hexaferrites: A Comparison Study of AC Susceptibility,FC-ZFC and hyperfine interactions

This study compares the AC susceptibility, FC-ZFC and hyperfine interactions of Sr(Co_xZr_x)Fe_12−2xO₁₉ and Sr(Ni_xZr_x)Fe_12−2xO₁₉ hexaferrites (HFs) manufactured via ultrasonic route. The formation of M-type hexaferrites have been confirmed by X-ray powder diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR) and high-resolution transmission electron microscopy (HR-TEM) techniques. Scanning electron microscopy (SEM) presented the hexagonal-platelet morphology of products. The variation in isomer shift, line width, quadrupole splitting and hyperfine magnetic field values of them have been governed by ⁵⁷Fe Mössbauer spectroscopy which showed that Co²⁺ and Zr⁴⁺ ions located at generally octahedral and 2b sites, while Ni²⁺ and Zr⁴⁺ ions located at octahedral 12k and 4f₂ sites. Measurements of magnetization versus temperature (M-T) and AC susceptibility versus temperature were carried out. The various synthesized HFs displayed ferrimagnetic behavior in the temperature interval of 10–325 K. Super-spin glass-like behavior was noticed at lower temperatures. Neel-Arrhenius and Vogel-Fulcher models were used to explore the experimental AC susceptibility. It was showed that a lower Co-Zr substitution content leads to strengthen the magnetic exchange interactions, however even low Ni-Zr substitution content provoke a reduction in magnetic exchange interactions.     

Electron spin resonance study of a CuIr2S4 single crystal

A spinel sulphide CuIr₂S₄ single crystal, which exhibits an orbitally induced Peierls phase transition at ～230?K, is investigated by electron spin resonance (ESR) spectroscopy. The phase transition is clearly manifested on the ESR spectra. It is suggested that the ESR signals are produced by a few non-dimerized Ir⁴⁺ ions. Moreover, an extra ESR spectrum appears at low temperature in addition to the paramagnetic ESR signals of Ir⁴⁺ ions, which is suggested to be caused by the Jahn–Teller effect of the non-dimerized Ir⁴⁺ ions. From the ESR results, it is found that the Jahn–Teller splitting energy ΔE _JT is much smaller than the spin-dimerization gap.     

Influence of zeolite water on paramagnetic and ferromagnetic resonances in the Co2[Nb(CN)8] · 8H2O molecular magnet

The contributions of Co²⁺ and Nb⁴⁺ ions to the high-frequency dynamic magnetic susceptibility of the Co₂[Nb(CN)₈] · 8H₂O molecular magnet in the paramagnetic state at T > 12 K are separated. It is found that the ferromagnetic ordering, which leads to the reconstruction of the electron paramagnetic resonance spectrum into the ferromagnetic resonance spectrum, occurs at T < 12 K. The influence of zeolite water on the spectra of the paramagnetic and ferromagnetic resonances is found. Dehydration leads to a decrease in the time of the spin relaxation of the ferromagnetic system from 50 ps to 17 ps at T = 4 K and to the variation in the temperature dependences of the widths of the lines and g factors in the electron spin resonance spectra.