Growth,structure and physical properties of gadolinium doped Sr2IrO4 single crystal

A series of Gd-doped Sr₂IrO₄ single crystals were grown using a flux method. Analysis of the temperature-dependent resistance of these crystals reveals that these samples show two-dimensional weak localization at 150 to 300 K, while three-dimensional variable range hopping (VRH) behavior is observed at temperatures lower than 150 K. Two localization lengths are observed in the VRH behavior, with a transition temperature of around 88 K. Correspondingly, temperature-dependent magnetization observations along the ab-plane reveal magnetic anomalies at both 150 and 85 K. This work demonstrates the correlation between the electrical and magnetic properties of 5d transition-metal compounds.     

Phase separation with charge self-organization in the Tb0.95Bi0.05MnO3, Gd0.75Ce0.25Mn2O5, and Eu0.8Ce0.2Mn2O5 manganite multiferroics

New doped manganite multiferroics Tb_0.95Bi_0.05MnO₃, Gd_0.75Ce_0.25Mn₂O₅, and Eu_0.8Ce_0.2Mn₂O₅, which are semiconductors, have been grown and studied. The starting dielectric multiferroics TbMnO₃ and RMn₂O₅ (R = Gd and Eu) have close magnetic and ferroelectric ordering temperatures of 30–40 K. The crystals studied are multiferroics in which states with giant permittivity and ferromagnetism coexist at room temperature. An analysis of the dielectric properties suggests that, at temperatures T ≥ 180 K, these crystals undergo a phase separation involving dynamic periodic alternation of quasi-2D layers of mixed-valence manganese ions, a process accounting for the onset of charge-induced ferroelectricity. At low temperatures (T < 100 K), a small phase volume in the crystals is occupied by as-grown quasi-2D layers containing dopants and carriers. Most of the crystal volume is occupied by the carrier-free dielectric phase. Thermally activated hopping conduction involving carrier self-organization in the crystal matrix with ferroelectric frustrations drives a phase transition to the state of charge-induced ferroelectricity at T ∼ 180 K. Original Russian Text ? V.A. Sanina, E.I. Golovenchits, V.G. Zalesskiĭ, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 5, pp. 874–882.     

Magnetic properties of CuCr2Se4 single crystals

The magnetic properties of CuCr₂Se₄ single crystals, which were grown by chemical transport reactions using iodine as a carrier, have been investigated. The magnetic moment at 0 K is found to be 5.07 μ_B per mole. The susceptibility at high temperatures follows a Curie-Weiss law with an asymptotic Curie temperature 430 K and a Curie constant 2.55 emu · $\text{deg}\text{mol}$. The magnetocrystalline anisotropy constants K₁ and K₂ are ? 6.9x 10⁵ and ? 0.9x 10⁵$\text{erg}\text{cm}{}^3$, respectively, at 5.1 K.In order to examine the effects of annealing on the magnetocrystalline anisotropy, the ferromagnetic resonance at room temperature was measured after annealing in vacuum and subsequently in an atmosphere of Se. It is found that the absolute values of K₁ and K₂ decrease after annealing in vacuum and increase to the initial values after annealing in an atmosphere of Se.     

Effect of chirality on the dynamics of domain walls in the molecular ferrimagnet [MnII(HL-pn)(H2O)][MnIII(CN)6] · 2H2O

The contributions from modes of switching, sliding, creep, and Debye relaxation of pinned domain walls to the low-frequency magnetic properties of the chiral and racemic molecular ferrimagnets [Mn^II(HL-pn)(H₂O)][Mn^III(CN)₆] · 2H₂O have been separated. It has been found that the chirality of the atomic and spin structures affects the temperatures of the transitions from the sliding mode to the creep mode and from the creep mode to the mode of Debye relaxation. In the chiral crystals, transitions to the creep and Debye relaxation modes have been observed at temperatures T = 7 and 5 K, respectively. In the racemic crystals, these transitions have been observed at temperatures T = 13 and 9 K, respectively, all other factors being equal.     

Inhomogeneous ferrimagnetic-like behavior in Gd2/3Ca1/3MnO3 single crystals

We present a study of the magnetic properties of Gd_2/3Ca_1/3MnO₃ single crystals at low temperatures, showing that this material behaves as an inhomogeneous ferrimagnet. In addition to small saturation magnetization at 5 K, we have found history dependent effects in the magnetization and the presence of exchange bias. These features are compatible with microscopic phase separation in the clean Gd_2/3Ca_1/3MnO₃ system studied.     

Thermoelectric power of TTT2I3+δ

We have measured the thermoelectric power of crystals of TTT₂I_3+δ with conductivity maximum occuring at temperatures from 110 K to 38 K. We find that the metallic state is stabilized to lower temperatures as the samples become less stoichiometric, that the change in electron concentrations on TTT varies by about 5% over this range and that Coulomb correlations are small in this compound.     

Optical band-gap of Zn3As2

Absorption measurements of single Zn₃As₂ crystals were made at temperatures 5, 80 and 300 K. Free-carrier absorption is interpreted in the simple classical model. Interband absorption shows contributions from Urbach-like excitations. The direct optical gap has been estimated as 0.99 eV at 300 K, 1.09 eV at 80 K and 1.11 eV at 5 K. The linear dependence of band-gap on temperature was found in the range 80–300 K with dE_g/dT = ? 4.55 × 10^?4eVK^?1.     

Crystal field effects on the magnetic and hyperfine properties of Yb3+ in ytterbium ethylsulfate

The magnetic and hyperfine properties of Yb³⁺ in Yb(C₂H₅SO₄)₃·.9H₂O have been studied using the crystal field (CF) obtained from an analysis of the observed absorption spectra of the crystal. The principal magnetic susceptibilities are in reasonable agreement with those observed both at liquid oxygen and liquid helium temperatures. The observed reversal of magnetic anisotropy at 17.7K is also corroborated. The Schottky heat capacity shows a peak at around 40K. The magnetic hyperfine field due to the 4f electrons at the nucleus is found to be 1.79MG. The hyperfine heat capacity C_N has a Schottky anomaly at about 25 mK. Above 1K, in the liquid helium range, C_N follows a simple T^?2 law as observed by Cooke et al. It is concluded that in the rare earth ethylsulfates a single suitable CF gives a good account of the various properties from room temperature down to liquid He temperatures.     

Magnetic phase transitions,anisotropic susceptibility and dipolar interactions in antiferromagnetic MnNb2O6

The magnetic properties of MnNb₂O₆ single crystals have been studied in the temperature range 1.6–300 K (T_N = 4.4 K), in fields up to 220 kOe. The high field saturation at low temperature, as well as the paramagnetic susceptibility at high temperature, agree well with a ${}^6\text{S}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ state for Mn²⁺ ions. From 1.6 to 3.8 K a spin flop is induced by fields ranging from 17 to 21 kOe, applied in the direction of the a-axis. Elements of the magnetic susceptibility tensors up to rank 12, measured below the spin flop field, are in accordance with a magnetic anisotropy originating mainly from magnetic dipolar interactions.     

Ferromagnetism and spin reorientation in Sm12Fe14Al5

The single crystal of the new ternary compound Sm₁₂Fe₁₄Al₅ was grown and its crystallographic and magnetic properties were investigated. Sm₁₂Fe₁₄Al₅ has a hexagonal structure of the space group p-3m1 and shows ferromagnetism with a Curie temperature of 245 K. The easy direction of magnetization is parallel to the c-axis at temperatures between 245 and 85 K; however, it changes to the c-plane below 85 K through a first-order-like phase transition. No saturation is observed in the magnetization curve even under the applied field of 55 kOe at 5 K. Sm₁₂Fe₁₄Al₅ seems to have a large coercive field at very low temperatures. The anisotropy field was estimated at 5 and 120 K and the saturation magnetization of low temperature phase is explained assuming a ferromagnetic coupling between Fe and Sm sublattices.     

Antiferromagnetic order and spin glass behavior in Dy2CuIn3

The magnetic properties of the intermetallic compound Dy₂CuIn₃ have been investigated. Ac and dc-susceptibility measurements indicate an onset of antiferromagnetic ordering at T_N=19.5 K and an additional frequency dependent transition at T_ds∼9 K. Neutron diffraction studies confirm the ordered transition at 19.5±1 K. The magnetic unit cell can be described by the propagation vector k=(0.25,0.25,0) with the magnetic moment μ=2.63(4)μ_B/Dy³⁺ parallel to the c-axis. Nevertheless, neutron diffraction reveals no additional magnetic phase transition around or below 9 K, which suggests that, at lower temperatures, a spin glass state may be formed in coexistence with the antiferromagnetic mode as a result of frustration and the antagonism between ferromagnetic and antiferromagnetic exchange interactions.     

Magnetic and structural studies of the alloy system REIn0.5Ag0.5

The structural and magnetic properties of the alloy system REIn_0.5Ag_0.5 [RE = Gd, Tb, Dy, Ho, Er, Tm and Yb] are reported. All these alloys (except that of Yb) crystallize in a cubic CsCl type structure at room temperature. Low temperature X-ray diffraction data does not reveal any structural phase transformation down to 8 K. On the basis of magnetic susceptibility data at a different temperature (3–300 K) and applied magnetic field (2 × 10⁵ to 8 × 10⁶ A m^-1, it has been concluded that GdIn_0.5Ag_0.5 is ferromagnetic (T_c = 118 K), TbIn_0.5Ag_0.5 and DyIn_0.5Ag_0.5 are meta magnetic (T_N = 66 and 30 K, respectively) and alloys involving Ho, Er, Tm and Yb are ferrimagnetic with Néel temperatures (T_N) equal to 24, 22, 21 and 20 K, respectively. The evaluated effective magneton number (p) is found to be slightly larger compared to theoretical values for tripositive ions of Gd, Tb and Dy and a bit smaller for Ho, Er, Tm and Yb. The results have been qualitatively explained using appropriate theories.     

A neutron diffraction study of the magnetic properties of PrTiO3 and NdTiO3

The magnetic properties of PrTiO₃ and NdTiO₃ were studied by neutron diffraction at several temperatures below 110 K. Although PrTiO₃ exhibits a T_N at 90 K no significant magnetic scattering was detected down to 65 K. The order at 90 K can be attributed to the Ti(III) below our detection limit of 0.25μ_B. Below 65 K magnetic reflections due to the Pr(III) sublattice develop consistent with a F_xC_y configuration. At 7 K the moment is 1.35(15)μ[inB] and lies at 45° (5) to the a or b axes. This structure is contrasted with that found for PrCrO₃. By comparing powder data at 50 and 7 K for NdTiO₃ it is concluded there is no evidence for magnetic order on either the Nd(III) or Ti(III) sublattices in agreement with bulk magnetic properties. The decrease in magnitude of the Ti(III) moment from LaTiO₃ to NdTiO₃ is compared to the known behavior of the La_1-xY_xTiO₃ system and is found to be consistent.     

Magnetic properties of RAu2Si2 rare earth compounds

The magnetic properties of the R Au₂Si₂ compounds with R = Ce-Er have been investigated. It was found that the compounds for which R = Ce, Sm, Gd, Tb and Dy are antiferromagnetically ordered at temperatures ranging from 5.7 to 15.9°K. PrAu₂Si₂ and NdAu₂Si₂ exhibit paramagnetic behavior for temperatures as low as 4.2°K. The magnetic structure is ferrimagnetic for the compounds in which R = Eu, Ho, and Er. The Eu compound is in the divalent state. The Néel and Curie points for this system do not follow the De-Gemnes function. Curie-Weiss Behavior is exhibited by all the compounds with effective moments in good agreement with that of a free tripositive lanthanide ion. The difference in magnetic properties between R Au₂Si₂ and the isomorphous R Fe₂Si₂ series is discussed.     

Magnetic and dielectric behaviors of Ba0.2Sr0.8Co0.8Fe0.2O3-δ oxide

Ba_0.2Sr_0.8Co_0.8Fe_0.2O_3-δ (BSCFO) ceramic oxide has been synthesized by combined citrate-EDTA complexing method and studied with regard to their structural, magnetic and dielectric properties. It is shown that the compound exhibits perovskite-type cubic structure. It depicts hysteresis loop in presence of magnetic field—indicating its magnetic nature. The dielectric properties of sintered oxide were investigated in temperature range (373-873 K) and frequency (100 kHz-1 MHz).The ferroelectric and ferrimagnetic transition temperatures were found to be around 700 K.     

Magnetic properties of Sn1-xCrxTe crystals

Magnetization measurements of magnetic semiconductor Sn_1-xCr_xTe (x <5 at%) crystals with the Curie temperature T_c = 150–300 K were made down to 2 K. The magnetic properties are sensitive to isothermal annealing under Zn vapor. The overall magnetizations of the Zn-annealed crystals have paramagnetic and ferro- or antiferromagnetic contributions.     

Floating zone growth and magnetic and specific heat properties of La0.67Ca0.33Mn1-xFexO3（x=0.00,0.04）single crystals

Single crystals of La_0.67Ca_0.33MnO₃ and La_0.67Ca_0.33Mn_0.96Fe_0.04O₃ were obtained by floating zone method. Laue diffraction pattern and rocking curve of the single crystals show that their quality is good. The magnetic behaviours of these compounds have been studied. Fe doping significantly depresses the magnetic contribution to the total specific heat C_P, but slightly influences the lattice contribution at temperatures above 50K. The peak of C_P shifts towards high temperatures with increasing magnetic field. Both single crystals exhibit the first-order magnetic transition around the Curie temperature.     

Field-induced structural transition and the related magnetic entropy change in Ni43Mn43Co3Sn11 alloy

Magnetic properties and magnetic entropy change ΔS were investigated in Heusler alloy Ni₄₃Mn₄₃Co₃Sn₁₁. With decreasing temperature this alloy undergoes a martensitic structural transition at T_M=188 K. The incorporation of Co atoms enhances ferromagnetic exchange for parent phases. Austenitic phase with cubic structure shows strong ferromagnetic behaviors with Curie temperature T_C^A at 346 K, while martensitic phase shows weak ferromagnetic properties. An external magnetic field can shift T_M to a lower temperature at a rate of 4.4 K/T, and a field-induced structural transition from martensitic to austenitic state takes place at temperatures near but below T_M. As a result, a great magnetic entropy change with positive sign appears. The size of ΔS reaches 33 J/kg K under 5 T magnetic field. More important is that the ΔS displays a table-like peak under 5 T, which is favorable for Ericsson-type refrigerators.     

Magnetic properties of V5S8 single crystals

The magnetic properties of V₅S₈ single crystals have been investigated by susceptibility and torque measurements. The susceptibilities parallel and perpendicular to the magnetic easy axis show a remarkable anisotropy below the Neel temperature of 32 K and are nearly Isotropie above that temperature. The easy axis is found to be nearly along the c-axis of the monoclinic lattice, being inclined at an angle of 9.6 ± 1.0° from the c-axis toward the a-axis. The torque curves, measured up to 24.4 kOe at liquid helium temperature, deviate from the usual form of a sine function with increasing magnetic field. The analysis of these torque curves suggests that spin flopping may occur at 43 kOe, a comparatively low critical field. Using these experimental results, a localized d-electron model for a particular site of the vanadium-ion, proposed by previous investigators, is examined.     

Intrinsic inhomogeneity and non-linear conduction in charge-ordered Bi0.5Ca0.4Sr0.1MnO3

Systematic studies of X-ray, magnetic, electronic transport, and elastic properties have been performed on polycrystalline Bi_0.5Ca_0.4Sr_0.1MnO₃ sample. The sample exhibits charge ordering (CO) state below T_CO (=304 K), accompanied by a distinct maximum in magnetization. The softening of Young's modulus in the vicinity of T_CO indicates that there is a strong coupling of electron-phonon due to Jahn-Teller (JT) effect. The dynamic ferromagnetic spin correlations are observed at high temperatures above T_CO, which are replaced by antiferromagnetic (AFM) spin fluctuations at a concomitant CO transition. Below 32 K, a spin-glass (SG) state dominates at low temperatures. The voltage-current (V-I) characteristics measurement results indicate that the non-linear conduction starts above a threshold current, giving rise to a region of negative differential resistance (NDR). The origin of the non-linear conduction is discussed in view of current induced collapse of CO state associated with phase-separation mechanism.