Susceptibility Of Single Crystals Research Articles

Neutron-Scattering Study of Magnetism in Single-CrystalCu1-xZnxGeO3

A recent study of the magnetic susceptibility in single crystals of the spin-Peierls material CuGeO 3 doped with Zn indicates antiferromagnetic order at low temperatures. In the present publication, we report a neutron scattering investigation of the static and dynamic magnetic properties of single-crystal Cu 0.966 Zn 0.034 GeO 3 . Below the transition temperature of 4.2 ± 0.3 K, sharp magnetic Bragg peaks are observed at the magnetic superlattice positions (0 k l /2) with both k and l odd. However, the intensities of these peaks are not saturated even at 1.4 K, and the long range ordered magnetic moment is only ∼0.2 µ B per Cu site. Moreover, no well-defined spin-wave-like excitations are seen. Instead, overdamped magnetic excitations appear around the magnetic Bragg peaks at low temperatures. These results suggest an unusual state of magnetic order incorporating considerable magnetic and possibly structural disorder. We speculate that this unusual order is caused by a spatial distribution of spin states...

Transport Properties in LaAg and CeAg Single Crystals

We have measured the Hall effect, magnetoresistance, thermoelectric power, magnetic susceptibility and magnetization in CeAg and LaAg single crystals. We observed clear anomalies related with a ferromagnetic transition at 5.5 K and a quadrupolar ordering at 17 K both in the Hall effect and magnetic susceptibility for CeAg.

Electric and Magnetic Low-Temperature Phase Transitions ofYbMn2O5

We made measurements of dielectric constant, pyroelectric current, magnetic susceptibility and magnetoelectric effect of single crystals of YbMn 2 O 5 . From the results, we concluded that there were two phase transitions besides antiferromagnetic transition at approximately 40 K. The first transition at 32 K is characterized by a peak of dielectric constant, a kink of magnetoelectric polarization and an appearance of pyroelectricity below this temperature. It was considered to be electric in nature. The second one is at 6 K. It is also accompanied by another peak of dielectric constant, a steep rise of pyroelectricity and anomalies of both magnetic and magnetoelectric susceptibilities. We suppose that the ordering of Yb 3+ magnetic moments begins to develop at this temperature, involving a change in the crystal structure and then in spontaneous polarization. The low temperature phase has a magnetic field-induced transition which occurs at about 19 kOe at 4.2 K.

Second order phase transition in Er and Tm metals

Study of the magnetic susceptibility, electroresistivity and specific heat of Er and Tm single crystals allowed us to conclude that at the Neel points of these metals a second order phase transition occurs. At the same time we detected some significant differences of the character of transformation from the theoretical predictions for systems with two-component order parameter. Near the TN one can see additional anomalies testifying to the presence of intermediate phases probably of the soliton type.

Field induced transition of the AC susceptibility in high-Tc superconductors

We have investigated the angle and field dependence of the ac susceptibility in Bi2Sr2CaCu2O8 single crystals at low external fields. The ac field was applied perpendicular to the CuO2 planes. The first and third harmonic of the ac susceptibility exhibit a remarkably sharp transition when the dc field component perpendicular to the CuO2 planes crosses a threshold field Hth. Hth is strongly temperature dependent, but is independent of the parallel field component. We prove that these structures are related to the irreversibility line and propose a simple model which excellently explains the measurement data.

Oxidation state and magnetic properties of Pb2Sr2Tb1-xYxCu3O8.

${\mathit{L}}_{3}$-edge x-ray absorption, inelastic neutron scattering (INS), and magnetic susceptibility experiments are used to characterize the electronic properties of Tb in ${\mathrm{Pb}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{TbCu}}_{3}$${\mathrm{O}}_{8}$. The x-ray absorption results indicate that Tb is trivalent and show no evidence for strong hybridization between Tb and the ${\mathrm{CuO}}_{2}$ bands. The observation of three peaks of magnetic origin in the INS experiments is also a clear indication of the trivalent state of Tb. These peaks are assigned to crystalline electric-field (CEF) transitions, and their energies and intensities are consistent with the CEF potential expected for a trivalent rare earth in the ${\mathrm{Pb}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{RCu}}_{3}$${\mathrm{O}}_{8}$ lattice. The low-energy response in the INS spectra at low temperatures is described using the mean-field approximation. Single crystal and polycrystalline susceptibilities show deviations from calculations and differ from magnetically diluted samples. These deviations are observed for temperatures less than 120 K and we interpret this as the onset temperature of the magnetic Tb-Tb short-range correlations. This interpretation is supported by the temperature dependence of the magnetic INS intensities at low energies. The onset temperature, estimated at 120 K, is more than an order of magnitude higher than seen in any related system, as well as much higher than the two-dimensional long-range ordering temperature at T=5.5 K. This unusual behavior is understood in terms of the highly two-dimensional nature of the lattice combined with the strongly Ising-like magnetic properties. In addition to the Tb-Tb correlations, the susceptibility experiments on a magnetically dilute sample indicate a weak rare-earth Cu exchange interaction.

Magnetic and thermal properties of U xLa 1− xPd 2Al 3

We present the experimental results of the specific heat, magnetic susceptibility and electrical resistivity of single crystals of U x La 1− x Pd 2Al 3. As the uranium atom is replaced by the lanthanum atom, the Néel tem x = 0.5, the ferromagnetic phase transition occurs and the feature is similar to a weak itinerant ferromagnet. It is found that both the electrical resistivity and the magnetic susceptibility cannot be scaled with uranium concentration. The temperature dependence of the electrical resistivity suggests the local nature of the spin fluctuations.

Effect of diamagnetic dilution on the [formula omitted] square Heisenberg antiferromagnet

Copper (II) formate tetrahydrate (CFTH) is a good example of a two-dimensional (2D) square Heisenberg antiferromagnet with S = 12. Three-dimensional ordering, driven by weak inter-planar exchange, occurs at a temperature, TN, of 16.5 K. We have measured the dc susceptibility of single crystals in which up to 11% of the Cu2+ ions have been replaced by diamagnetic Zn2+ ions. TN decreases linearly with dopant concentration, x, and the behaviour is very similar to that seen in La2CuO4 and in CFTH when studied by ESR spectroscopy. Our results also show an increase in the susceptibility below TN as x increases due to the larger number of uncompensated moments in the diluted material.

Neutron spectroscopy and anisotropy of the magnetic properties of UOS: interpretation in a crystal-field and molecular-field model

Uranium oxysulphide is an ionic compound whose magnetic and thermodynamic properties have been extensively studied in the past. UOS becomes antiferromagnetic below T N = 55 K with an ordered moment μ ord ≅ 2 μ B. A previous neutron crystal field (CF) spectroscopy experiment was performed to observe the splitting of the J = 4 ground manifold. Two possible CF level schemes were proposed in order to interpret the results, differing essentially for the presence of the intense Г (1) t5 → Г t4 transition at low energy (<10 meV). One of the aims of this work was to look for a peak in this range of energy, which was not accessible at the time of the first experiment. Another goal was to test the CF model against a careful study of the anisotropic magnetic susceptibility of high-quality single crystals. The results of these new measurements are presented and discussed in the frame of a self-consistent molecular field model taking into account the exchange anisotropy.

Neutron spectroscopy and anisotropy of the magnetic properties of UOS: Interpretation in a crystal-field and molecular-field model

Uranium oxysulphide is an ionic compound whose magnetic and thermodynamic properties have been extensively studied in the past. UOS becomes antiferromagnetic below TN = 55 K with an ordered moment μord ≅ 2μB. A previous neutron crystal field (CF) spectroscopy experiment was performed to observe the splitting of the J = 4 ground manifold. Two possible CF level schemes were proposed in order to interpret the results, differing essentially for the presence of the intense Г(1)t5 → Гt4 transition at low energy (<10 meV). One of the aims of this work was to look for a peak in this range of energy, which was not accessible at the time of the first experiment. Another goal was to test the CF model against a careful study of the anisotropic magnetic susceptibility of high-quality single crystals. The results of these new measurements are presented and discussed in the frame of a self-consistent molecular field model taking into account the exchange anisotropy.

Spin susceptibility in underdoped YBaCuO single crystals from NMR

We report on 89Y, 63Cu and 17O NMR measurements in the normal state of YBaCuO single crystals (T c =91 K and T c =48 K). A comprehensive description of all NMR results is obtained starting from a spin susceptibility with a contribution from antiferromagnetic spin fluctuations delineated by the inelastic neutron scattering data, and a contribution from itinerant quasi-particles with a characteristic frequency increasing at low temperatures. For the first time a complete analysis is given for yttrium spin-lattice relaxation data.

Temperature Dependence of Exchange Narrowed ESR Linewidth of (MT)2(TCNQ)3·2 H2O Salt

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Magnetic studies on erbium bromate and the crystal field

Measurements of the principal magnetic susceptibilities of erbium bromate single crystals in the temperature range 300-15.5 K have been made. The anisotropy at 300 K is high (|Δ X/ X | = 0.15) and it increases very rapidly with decreasing temperature. The variation of X ⊥ is nearly Curie-type down to the lowest temperature attained, whereas the X | versus T plot is nearly flat. Smooth variation of X ⊥ down to 15.5 K does not indicate any structural phase transition of the crystal. The observed magnetic properties were analyzed for the first time invoking an effective electrostatic interaction of the Er 3+ ion with its diamagnetic surroundings; the crystal field (CF) conforms to the approximate site symmetry of Er 3+, i.e. D 3h. The CF J-J mixing was included through term diagonalization and intermediate coupling effects were partly taken care of using appropriate reduced matrix elements. The computed values are in very good agreement with the corresponding observed values. Our computed values of X | in the range 60–500 mK reproduced the same sort of behavior as predicted by Simizu et al. in 1984. The thermal and hyperfine properties have been worked out.

ESR study of deuterated organic conductor (D 8-ET) 2[Hg(SCN) 2Cl

The electron spin resonance g factor, linewidth and spin susceptibility of single crystals of a fully deuterated bis(ethylenedithio)tetrathiafulvalene (D 8-ET) based conductor with Hg(SCN) 2Cl − anions are presented. The spin susceptibility of the salt is thermally activated with anomalies near the metal-insulator phase transition and a maximum of the electrical conductivity. A discussion of the ESR parameters is given.

Dielectric relaxation associated with ionic hopping transport in KTiOPO4single crystal

Abstract By means of the measurement of complex dielectric susceptibilities of KTP single crystal, a new dielectric relaxation has been found in KTP below 300°C. The origin of relaxation may be due to the hopping transport of K+ions. Consequently, it is confirmed that Vogel-Fulcher law well describes the dielectric relaxation in KTP.

Measurement of optical nonlinear susceptibility of CdS single crystal using a single beam

We report a measurement of optical nonlinear susceptibility of CdS using the Z-scan method. The input laser light irradiating on the CdS single crystal had a wavelength of 514.5 nm and a flux density of 16 kW/cm 2. We estimate a nonlinear susceptibility of X (3) = 3.5 × 10 -9 (esu) being in agreement with an anharmonic oscillator model based on excitons. We also found that when a DC electric field was added on the sample of CdS, the nonlinear absorption increased as the applied DC electric field was increased.

Single crystal susceptibility of the S = 1 one-dimensional Heisenberg antiferromagnet AgVP 2S 6

A reliable single crystal susceptibility data is reported to reveal the ground state property of the S = 1 one-dimensional Heisenberg antiferromagnet AgVP 2S 6. The observed susceptibilities for the parallel and perpendicular direction to the chain axis fall down rapidly as the temperature is lowered down to about 50 K, revealing a non-magnetic singlet ground state nature of the system. The results are interpreted quantitatively within the framework of the Haldane prediction, giving the quantum gap of E g k B ≈ 250 K which should be compared with 320 K from neutron scattering.

ESR Study of Deuterated Analogue of (BEDT‐TTF)4Hg3I8

AbstractElectron spin resonance g‐factor, linewidth, and spin susceptibility of single crystals of the fully deuterated bis(ethylenedithio)tetrathiafulvalene (D8‐(BEDT‐TTF)) based conductor with octaiodine‐ mercurate anion (Hg3I8)2‐ are found to show pronounced temperature dependences between 4 and 300 K. A first‐order phase transition of the type semiconductor‐semiconductor is observed at 258 K. Discussion of the ESR parameters and the nature of the phase transition is given.

Intercalation of n-alkylamines in iron thiohypophosphate (FePS3)

The intercalation of linear alkylamines (C1-C4) in the two-dimensional (2D) Ising antiferromagnet, FePS3, has been investigated. Intercalation proceeds with a dilation of the interlayer distance. The expansion (approximately 3.8 angstrom) is the same for all four amine molecules, suggesting that they are oriented flat with respect to the layers. From an analysis of the products of deintercalation, it is concluded that the intercalated species are the alkylammonium cations and neutral amine molecules. The intercalated compounds are highly moisture sensitive, as reflected in the chemical nature of the intercalated species. Charge neutrality of the lattice after intercalation is preserved by the loss of Fe2+ ions from the lattice. These Fe2+ ions are further oxidized to form superparamagnetic Fe2O3 clusters, as confirmed by Mossbauer spectra and magnetic measurements. This was further corroborated by in situ EPR studies. The Fe-57 Mossbauer spectra of the intercalated compounds showed evidence for two species other than Fe2O3. On the basis of the observed isomer shifts and quadrupole splittings, they have been assigned to Fe2+ in an environment similar to that in FePS3 and in a distorted FePS3 environment. The temperature and field dependence of the magnetic susceptibility of single crystals of the amine-intercalated FePS3 have been measured. Their magnetic behavior shows many of the features expected of a 2D Ising antiferromagnet with random defects, Fe1-xPS3, in agreement with the mechanism of intercalation.

A contactless vibrating sample technique for the measurement of normal state resistivity, AC susceptibility and magnetization of single crystals of high Tc superconductors

The technique relies on a measurement of the out-of-balance signal from an AC (5-100 kHz) bridge, one arm of which contains a coil into and out of which the specimen is vibrated. Locked-in detection at both the AC and the vibration frequencies leads to high sensitivity, sufficient to measure the resistivity of a small high-Tc crystal in the normal state, as well as the real and imaginary parts of the susceptibility in the superconducting state. A simple modification of the circuit, with no disturbance to the specimen, allows the apparatus to be used as a vibrating sample magnetometer.