Influence of Pr-doping on structural, electronic transport, magnetic properties of perovskite molybdates Sr1−xPrxMoO3 (0≤x≤0.15)

The effect of Pr-doping on structural, electronic transport, magnetic properties in perovskite molybdates Sr_1−xPr_xMoO₃ (0≤x≤0.15) has been investigated. The Pr-doping at Sr-site does not change the space group of the samples, but decreases the lattice parameter a. The magnitude of resistivity ρ increases initially (x≤0.08) and then decreases with further increasing Pr-doping level x and ρ(T) behaves as T² and T dependence in the low-temperature range blow T* and high-temperature range of 150 K<T<350 K, related to the electron-electron (e-e) and electron-phonon (e-ph) scattering, respectively. The magnetic susceptibility χ value of the sample increases with increasing x and the χ(T) curve for all samples can be well described by the model of exchange-enhanced paramagnetism. The specific heat magnitude in the low-temperature region increases with increasing Pr-doping level. The specific heat value agrees with the classical Dulong-Petit phonon specific heat, C_cl=3k_BrN_A=124.7 J/mol K in the high-temperature region and the temperature dependence of the specific heat can be well described by the formula C_p(T)/T=γ_e+β_pT² in the low-temperature range. These behaviors can be explained by the competition between the increase in the density of state (DOS) at Fermi energy level and the disorder effect due to Pr-doping.     

Influence of Ni doping on the properties of perovskite molybdates SrMo1−xNixO3 (0.02≤x≤0.08)

Systematic studies of the structural, transport, magnetic and specific heat behavior have been performed on the perovskite molybdates SrMo_1−xNi_xO₃ (0.02≤x≤0.08). Ni doping at the Mo site does not change the structure of all samples, but increases the lattice parameter a monotonically. All of the doped samples keep their metallic behavior. The magnetic properties keep a Pauli paramagnetism in the high-temperature region, but have a ferromagnetic (FM) transition at about 50 K. The resistivity, ρ, and magnetic susceptibility, χ, increase, while the electronic specific heat coefficient, γ_e, decreases monotonically with the increase of Ni doping content, x. The electronic transport of all samples shows a T² dependence in the low-temperature region and a T dependence in the high-temperature region, respectively. The temperature dependence of the specific heat can be well described by the formula C_p(T)/T=γ_e+β_pT² in the low-temperature range. These behaviors can be explained by the competition between the decrease in the density of states (DOS) at the Fermi level and the electron localization due to the disorder effect induced by the random distribution of Ni at the Mo site in the samples.     

Magnetic and transport properties of UPd2Sb

A new compound UPd₂Sb was prepared and studied by means of X-ray diffraction, magnetization, electrical resistivity, magnetoresistivity, thermoelectric power and specific heat measurements. The phase crystallizes with a cubic structure of the MnCu₂Al-type (s.g. ). It orders antiferromagnetically at T_N=55 K and exhibits a modified Curie-Weiss behaviour with reduced effective magnetic moment at higher temperatures. The electrical resistivity behaves in a manner characteristic of systems with strong electronic correlations, showing Kondo effect in the paramagnetic region and Kondo-like response to the applied magnetic field. The Seebeck coefficient exhibits a behaviour expected for scattering of conduction electrons on a narrow quasiparticle band near the Fermi energy. The low-temperature electronic specific heat in UPd₂Sb is moderately enhanced being about 81 mJ/mol K².     

Magnetism and Hall effect of the Heusler alloy Co2ZrSn synthesized by melt-spinning process

Magnetization and Hall resistivity have been measured for the Heusler alloy Co₂ZrSn synthesized by the melt-spinning process. The temperature dependence of magnetization follows the spin-wave theory at a low temperature. Abnormal behaviors are observed both in resistance and Hall effect below 8 K. The present Hall resistivity measurement shows that the anomalous Hall effects coexist with normal Hall effects. The negative value of normal Hall coefficient over the whole temperature range reveals that the major charge carriers are electrons. The anomalous Hall coefficient is proportional to the zero-field resistivity, suggesting that magnetic skew scattering is the dominant mechanism in the ferromagnetic regime. The reason for the abnormity below 8 K during transport is discussed.     

Magnetic-field-induced transition from metastable spin glass to possible antiferromagnetic-ferromagnetic phase separation in Cd0.5Cu0.5Cr2O4

Using ac susceptibility, dc magnetization and heat-capacity measurements, we have investigated the magnetic properties of Cd_0.5Cu_0.5Cr₂O₄. Cd_0.5Cu_0.5Cr₂O₄ has an extraordinary magnetic phase including a metastable spin-glass (SG) phase at zero field, a possible phase separation scenario of AFM/FM above ∼0.5 T field, and at intermediate fields, an apparent pseudo reentrant spin-glass (RSG) plateau is observed. These phenomena are closely correlated with the pinning effect of the Cu²⁺ sublattice on the frustrated lattice.     

Heat capacity of Heusler alloys: Ferromagnetic Ni2MnSb,Ni2MnSn,NiMnSb and antiferromagnetic CuMnSb

We report the results of the investigation of the specific heat of the ferromagnetic Heusler Ni₂MnSn, Ni₂MnSb, NiMnSb and antiferromagnetic CuMnSb alloys. The low-temperature behaviour of the specific heat may be described as C=γT+βT³ for ferromagnetic compounds and as C=γT+δ T²+βT³ for antiferromagnetic CuMnSb. The values of the density of states from the heat capacity measurements are higher than those from electronic band structure calculations. Debye temperatures are in a good agreement with those obtained from thermal expansion measurements. The Grüneisen parameter is calculated for Ni₂MnSn and CuMnSb from the magnetic contribution to the specific heat in the vicinity of T_C or T_N.     

Influence of preparation method on SrMoO4 impurity content and magnetotransport properties of double perovskite Sr2FeMoO6 polycrystals

The magnetic and electric properties of the Sr₂FeMoO₆ compound produced under different preparation conditions were studied. Depending on the preparation condition, a strong variation in the nonmagnetic SrMoO₄ impurity content was found, which in turn determined the metallic or semiconducting behavior of the resistivity of the Sr₂FeMoO₆ compound. There was also evidence that SrMoO₄ played a crucial role in modifying the low magnetic field intergrain tunneling magnetoresistance in Sr₂FeMoO₆. In addition, we have established a simple method to prepare the single phase Sr₂FeMoO₆ polycrystals.     

Magnetic properties of PrRh2Si2: A neutron diffraction study

The magnetic properties of polycrystalline PrRh₂Si₂ sample have been investigated by neutron diffraction measurements. Antiferromagnetic transition with an anomalously high ordering temperature (T_N∼68 K) is clearly observed in magnetic susceptibility, specific heat, electrical resistivity and neutron diffraction measurements. Neutron diffraction study shows that Pr³⁺ ions carry an ordered moment of 2.99(7)μ_B/Pr³⁺ and align along the crystallographic±c-directions for the ions located at the (0,0,0) and positions. The magnetoresistance at 2 K and 10 T is rather large (∼35%).     

Magnetic ordering in CeMnCuSi2

Temperature and field-dependent magnetization measurements on polycrystalline CeMnCuSi₂ reveal that the Mn moments in this compound exhibit ordering with a ferromagnetic (FM) component ordered instead of the previously reported purely antiferromagnetic (AFM) ordering. The FM ordering temperature, T_c, is about 120 K and almost unchanged with external fields up to 50 kOe. Furthermore, an AFM component (such as in a canted spin structure) is observed to be present in this phase, and its orientation is modified rapidly by the external magnetic field. The Ce L₃-edge X-ray absorption result shows that the Ce ions in this compound are nearly trivalent, very similar to that in the heavy fermion system CeCu₂Si₂. Large thermomagnetic irreversibility is observed between the zero-field-cooled (ZFC) and field-cooled (FC) M(T) curves below T_c indicating strong magnetocrystalline anisotropy in the ordered phase. At 5 K, a metamagnetic-type transition is observed to occur at a critical field of about 8 kOe, and this critical field decreases with increasing temperature. The FM ordering of the Mn moments in CeMnCuSi₂ is consistent with the value of the intralayer Mn–Mn distance R^a_Mn–Mn=2.890 Å, which is greater than the critical value 2.865 Å for FM ordering. Finally, a magnetic phase diagram is constructed for CeMnCuSi₂.     

Transport and magnetic properties of cobalt doped CeNiAl4

Electrical resistivity and thermoelectric power (TEP) have been measured in polycrystalline sample of CeNi_0.75Co_0.25Al₄. The magnetization measurements have been performed in oriented powder with a-axis of the crystallites parallel to the external magnetic field. All the data have been compared with its parent compound CeNiAl₄. In the range 120-300 K, the Seebeck coefficient is significantly higher for alloy than for the parent material and exhibits a peak at ∼150 K. R(T)/R(300) follows a logarithmic temperature dependence for all samples above 100 K, and rapidly decreases as the temperature is lowered. The decrement is much faster in the cobalt doped samples than in the parent compound, suggesting stronger electronic correlations in the former. Inverse magnetic susceptibility in oriented powder follows a Curie-Weiss law above 100 K and shows p_eff=2.7 slightly higher than that of the free Ce³⁺ ion value of 2.5.     

Violation of the Mott-Ioffe-Regel limit: high-temperature resistivity of itinerant magnets Srn+1RunO3n+1 (n=2,3,∞) and CaRuO3

Sr_n+1Ru_nO_3n+1 represents a class of layered materials whose physical properties are a strong function of the number of Ru-O layers per unit cell, n. These materials along with the paramagnetic CaRuO₃ shares two major characteristics, namely, robust Fermi liquid behavior at low temperatures and anomalous transport behavior featured by linear temperature dependence of resistivity at high temperature. There is no crossover separating such two fundamentally different states. In this paper, we report results of our study that systematically addresses anisotropy and temperature dependence of resistivity as a function of n for the entire Sr_n+1Ru_nO_3n+1 series and CaRuO₃ and for a wide temperature range of It is found that the anomalous transport behavior correlates with magnetic susceptibility and that the scattering mechanism(s) driving the anomalous transport behavior becomes stronger with reducing dimensionality.     

Magnetic and structural studies of the double perovskites Ba2REMoO6

A magnetic, electronic and structural study of the double perovskites Ba₂REMoO₆ (RE=Sm, Eu, Gd, Dy) has been performed. All materials crystallise in the cubic symmetry space group and the cell volume decreases as RE varies from Sm to Dy in accordance with Vegard's law. An antiferromagnetic transition is observed below T_N=130 and 112 K for RE=Sm and Eu, respectively. The Néel temperatures of these ordered rare earth molybdenum double perovskites are much higher than previously observed in double perovskites containing Eu or Sm and a 4d or 5d transition metal arranged in an ordered rock salt configuration. The high Néel temperatures arise due to a strong superexchange magnetic interaction via the Mo-O-RE-O-Mo pathway. All of the phases are electronically insulating and there is no evidence of magnetoresistance at any temperature.     

Crystal growth, spectroscopic and crystal field studies of [N(CH3)4]2MnCl4 and [N(CH3)4]2CoCl4 single crystals in the paraelectric phase

Single crystals [N(CH₃)₄]₂MnCl₄ and [N(CH₃)₄]₂CoCl₄ were grown by the slow evaporation technique from the super-saturated solutions. The samples obtained were undergone the X-ray and spectroscopic studies. Absorption spectra in the paraelectric phase at T=303 K have been recorded using the Shimadzu 160A double beam automatic scanning spectrophotometers. On the basis of the exchange charge model and Racah theory the crystal field parameters and Racah parameters have been calculated; all absorption bands for both crystals were given an assignment.     

Effect of Mg substitution on electromagnetic properties of (Ni0.25Cu0.20Zn0.55)Fe2O4 ferrite prepared by auto combustion method

The ferrite compositions of (Ni_0.25−xMg_xCu_0.2Zn_0.55)Fe₂O₄ with x=0.0$x=0.0$, 0.07, 0.13, 0.18, and 0.25 were synthesized through nitrate-citrate auto-combustion method. The as-burnt powders showed the presence of crystalline cubic spinel ferrite with about 19–22 nm crystallite sizes. The resultant powders were calcined at 700 °C/2 h and pressed ferrites were sintered at 950 °C/4 h. The initial permeability, magnetic loss and AC resistivity were measured in the frequency range 10 Hz–10 MHz. The permeability and AC resistivity were found to increase and the magnetic loss decreased with Mg substitution for Ni, up to x=0.18$x=0.18$. The very high permeability in the composition x=0.18$x=0.18$, was due to better densification, lower magnetostriction constant and inner stresses, etc. The AC resistivity of the composition was also highest. The composition would be better than NiCuZn-based material for more miniaturization of multi layer chip inductor.     

Mechanical magnetoresistance in broken cold-pressed CrO2 powder sample

Large negative magnetoresistance (MR)(|ΔR/R|=|[R(H)-_Rmax]/_Rmax|>50%)$\left(\left|\mathrm{\Delta }R/R\right|=\left|[R(H)-R_{\max }]/R_{\max }\right|>50\%\right)$ has been observed in the broken cold-pressed CrO₂ powder samples near the room temperature, which is ascribed to the magnetic field-induced mechanical contact variation. This large, room-temperature negative MR might easily lead to a wrong conclusion that the spin-polarization is still very high at high temperatures. This observation may also point to the possibility to develop field sensors based on the mechanical MR.     

Optical absorption spectrum and local symmetry of Tm ion in TmAl3(BO3)4 crystal

With the help of group theory analysis of absorption spectra of the transition ³H₆ → ³F₃ of Tm³⁺ ion in TmAl₃(BO₃)₄ crystal, measured at several temperatures from 1.8 till 293 K, it has been shown, that the local symmetry of the Tm³⁺ environment is C₃ and it decreases to C₁ at a low temperature. Effective selection rules and polarizations of lines at high enough temperatures (when the line-width is larger than the splitting in C₃ symmetry) have been obtained.     

Antiferromagnetism and spin-glass transition in the FeInxCr2−xSe4 series of selenides

The magnetic behavior of the FeIn_xCr_2−xSe₄ system (with x=0.0, 0.2 and 0.4) has been investigated by magnetic and Mössbauer spectroscopy. Hyperfine parameters indicate that iron is in the Fe²⁺ oxidation state, with a minor (∼9%) Fe³⁺ fraction, located at different layers in the structure. Low-field magnetization curves as a function of temperature showed that the antiferromagnetic (AFM) order temperature is T_N=208(2) K for FeCr₂Se₄ and decreases to 174(3) K for FeIn_0.4Cr_1.6Se₄. The effective magnetic moment μ_eff decreases with increasing In contents, and shows agreement with the expected values from the contribution of Fe²⁺ (⁵D) and Cr³⁺ (⁴F) electronic states. A second, low-temperature transition is observed at T_G∼13 K, which has been assigned to the onset of a glassy state.     

Magnetic and transport properties of YbRhIn5 and YbIrIn5 single crystals

Single crystals of YbRhIn₅ and YbIrIn₅ have been grown by flux method. The crystals were characterized by means of X-ray diffraction, magnetic and electrical transport measurements. Both compounds were found to be weak diamagnets with metallic character of the electrical conductivity and the Seebeck coefficient.     

The effect of pressure on the spin density wave transition in the layered cobaltites [Ca2CoO3]0.62[CoO2] and [Ca2Co4/3Cu2/3O4]0.62[CoO2]

In order to investigate the pressure effect on the magnetism in the layered cobaltites, positive muon spin rotation and relaxation μ⁺SR experiments have been carried out up to 1.3 GPa using c-aligned polycrystalline samples of [Ca₂CoO₃]_0.62[CoO₂] and [Ca₂Co_4/3Cu_2/3O₄]_0.62[CoO₂]. A transverse field μ⁺SR experiment indicates that the transition temperature to an incommensurate spin density wave IC-SDW state is independent of hydrostatic pressure up to 1.3 GPa for the both compounds. Furthermore, there are no changes in the spontanious muon precession frequency in zero field at 5 K even under 1.3 GPa. These results strongly suggest that the IC-SDW exists not in the rocksalt-type block ([Ca₂CoO₃] and/or [Ca₂Co_4/3Cu_2/3O₄]) but in the CoO₂ plane.     

Large coercivity and small exchange bias in Mn3O4 / MnO nanoparticles

Core/shell structured Mn₃O₄/MnO nanoparticles were prepared by arc evaporating metallic manganese in air. These nanoparticles show unconventional exchange bias phenomena, in which the Curie temperature of the ferrimagnetic Mn₃O₄ is lower than the Néel temperature of the antiferromagnetic MnO. The exchange bias field in Mn₃O₄/MnO nanoparticles is much smaller than that in Mn₃O₄/Mn nanoparticles, due to the weak interfacial exchange coupling. The coercivity of the Mn₃O₄ phase in nanoscale is almost three times greater than that of the bulk Mn₃O₄.