Large room temperature magnetoresistance in YSZ doped La0.67Ba0.33MnO3 composite

The temperature dependence of the resistivity for composite samples of (1−x)La_0.67Ba_0.33MnO₃+xYSZ(LBMO/YSZ) with different YSZ doping level of x has been investigated in a magnetic field range of 0-7000 Oe, where the YSZ represents yttria-stabilized zirconia (8 mol% Y₂O₃+92 mol% ZrO₂). With increasing YSZ doping level, the range of 0-10%, the metal-insulator transition temperature (T_P) decreases. However, the resistivity, specially the low temperature resistivity, increases. Results also show that the YSZ doping level has an important effect on a low field magnetoresistance (LFMR). In the magnetic field of 7000 Oe, a room temperature magnetoresistance value of 20% was observed for the composite with a YSZ doping level of 2%, which is encouraging for potential application of CMR materials at room temperature and low field.     

Magnetic properties of electron-doped Y1−xCexMnO3 compounds

Cerium-doped Y_1−xCe_xMnO₃ compounds have been prepared in single-phase form for x=0 to 0.10. X-ray diffraction (XRD) patterns could be analyzed by using P6₃cm space group. Temperature variations of ac susceptibility and magnetization measurements show that these Ce-doped materials exhibit weak ferromagnetic transition. The observed ferromagnetic transition is attributed to the double exchange ferromagnetic interaction between Mn²⁺ and Mn³⁺ ions due to electron doping. The M–H loops exhibit hysteresis along with linear contribution and were analyzed based on bound magnetic polaron (BMP) model. Increase in saturation magnetization and decrease in BMP concentrations have been observed with increase in Ce doping.     

Magnetic anomalies in single crystalline ErPd2Si2

Considering certain interesting features in the previously reported ¹⁶⁶Er Mössbauer effect, and neutron diffraction data on the polycrystalline form of ErPd₂Si₂ crystallizing in the ThCr₂Si₂-type tetragonal structure, we have carried out magnetic measurements (1.8–300 K) on the single crystalline form of this compound. We observe significant anisotropy in the absolute values of magnetization (indicating that the easy axis is c-axis) as well as in features due to magnetic ordering in the plot of magnetic susceptibility χ versus temperature T at low temperatures. The χ(T) data reveal that there is a pseudo-low-dimensional magnetic order setting in at 4.8 K, with a three-dimensional antiferromagnetic order setting in at a lower temperature (3.8 K). A new finding in the χ(T) data is that, for H∥〈1 1 0〉 but not for H∥〈0 0 1〉, there is a broad shoulder in the range 8–20 K, indicative of the existence of magnetic correlations above 5 K as well, which could be related to the previously reported slow-relaxation-dominated Mössbauer spectra. Interestingly, the temperature coefficient of electrical resistivity is found to be isotropic; no feature due to magnetic ordering could be detected in the electrical resistivity data at low temperatures, which is attributed to magnetic Brillioun-zone boundary gap effects. The results reveal the complex nature of magnetism of this compound.     

Susceptibility measurements on some R5In3 compounds

The magnetic susceptibility of some rare earth-indium compounds has been measured in the temperature range 4.2–300 K under a constant field of 1 kOe. The compounds with R = Gd, Tb and Dy are antiferromagnetic, having Néel temperatures between 4.2 and 78 K ; those with R = Ho, Er and Tm seem to be ferromagnetic with ordering temperatures probably below 4.2 K. Y₅In₃ presents a temperature independent susceptibility.     

The crystalline electric field ground states for Er,Dy and Tm in YAl2

Recently reported neutron diffraction and paramagnetic susceptibility results on alloys of Tm_x Y_1?x Al₂ are discussed with respect to electron spin resonance measurements on dilute alloys of Er, Dy and Tm in YAl₂. The crystalline electric field ground states for Er and Dy do not correspond to those one would expect from the neutron measurements nor is the Tm ground state confirmed.     

Low-field AC susceptibility in Pr1−xHoxMn2Ge2

We report the structure and magnetic properties of Pr_1−xHo_xMn₂Ge₂ (0.0≤x≤1.0) germanides by means of X-ray diffraction (XRD), differential scanning calorimetry (DSC) techniques and AC magnetic susceptibility measurements. All compounds crystallize in the ThCr₂Si₂-type structure with the space group I4/mmm. Substitution of Ho for Pr leads to a linear decrease in the lattice constants and the unit cell volume. The samples with x=0 and x=0.8 have spin reorientation temperature. The results are collected in a phase diagram.     

Magnetic phase diagrams of Ho1−xDyxNi2B2C

We performed the magnetization measurement on Ho_1−xDy_xNi₂B₂C single crystals (x=0.1, 0.2, 0.3, 0.4, and 0.6) with magnetic field applied perpendicular and parallel to the c-axis. But only for the magnetic field perpendicular to the c-axis, the increase of Dy³⁺ concentration affects the magnetically ordered states of HoNi₂B₂C compound and makes the phase diagram more complicated. The antiferromagnetic ordering state attributed to Dy³⁺ sublattice starts to appear from a case of x=0.2 and finally the magnetic phase diagram becomes analogous to that of DyNi₂B₂C as x is increased which is consistent with the neutron scattering result.     

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 properties of the compounds ThCO2Ge2 and ThCo2Si2

Rather old preparation of the compounds ThCo₂Ge₂ and ThCo₂Si₂ and their magnetic study in the temperature range 100–570 K, published by Omejec and Ban [Z. Anorg. Allg. Chem. 380 (1971) 111], indicated that both compounds ordered ferrromagnetically below 100 K. In order to verify the old data, polycrystalline samples of ThCo₂Ge₂ and ThCo₂Si₂ have been prepared by arc melting and subsequent annealing, and studied by X-ray diffraction at room temperature (RT), by superconducting quantum interference device (SQUID)-magnetization and AC-susceptibility measurements at 2–320 K, and by dc-magnetization measurements in variable magnetic fields up to 120 kOe at 5, 80, and 283 K. The magnetic measurements confirm the ferromagnetic ordering in both compounds, but with totally different Curie temperatures: ≈120(20) K for ThCo₂Ge₂ and above 320 K for ThCo₂Si₂. The paramagnetic values of ThCo₂Ge₂ and the ordering of both compounds are discussed and compared with the old results of Omejec and Ban.     

Neutron diffraction studies of Tb2Rh3Si5 compound

In this work neutron diffraction studies of Tb₂Rh₃Si₅ compound are reported. The compound crystallizes in the monoclinic crystal structure of Lu₂Co₃Si₅-type. At 1.5 K an antiferromagnetic ordering with a propagation vector k=(1/2;1/2;1/2) was observed. The Tb magnetic moments of 9.8(2) μ_B form a non-collinear magnetic structure. In the vicinity of Néel temperature of 8 K a change of the magnetic ordering is evidenced. The change seems to be connected with phase transition from commensurate to incommensurate sine-wave modulation of the Tb magnetic moments.     

Nuclear and magnetic order in Y(Ni,Mn)O3 manganites by neutron powder diffraction

Neutron powder diffraction experiments performed on two selected compositions of the yttrium-based solid solution YNi_xMn_1−xO₃ clearly reveal a nuclear order between the Ni²⁺ and Mn⁴⁺ ions in the half-substituted compound YNi_0.50Mn_0.50O₃, so that the crystal structure is no longer described in the conventional orthorhombic Pbnm space group, but in the monoclinic P2₁/n, all over the investigated temperature range (1.5-300 K). However, both X-rays diagrams and neutron patterns of the YNi_0.25Mn_0.75O₃ phase are indexed in the Pbnm orthorhombic-like symmetry, indicating that the Mn and Ni ions are randomly distributed on the octahedral sites.In addition, neutron diffraction points out that the nature of the magnetic ordering is strongly connected to the structural properties. Whereas no long-range 3D-magnetic ordering was detected for the Pbnm YNi_0.25Mn_0.75O₃ phase, the YNi_0.50Mn_0.50O₃ compound exhibits a magnetic transition at The magnetic structure consists of two collinear Mn⁴⁺ and Ni²⁺ ferromagnetic layers (F_x0F_z magnetic configurations) with saturated magnetic moment values of 2.25(2) and 1.57(2) μ_B for Mn⁴⁺ and Ni²⁺, respectively, at 1.5 K.     

Magnetic properties and magnetocaloric effect in Dy(Co1−xFex)2 alloys

Polycrystalline samples of Laves-phase alloys Dy(Co_1−xFe_x)₂(x=0$x=0$, 0.02,0.04,0.06,0.08) have been prepared by arc-melting method. No first order phase transition was observed for samples with x≠0$x\ne 0$. With the increase of Fe content, the Curie temperature increases greatly, while the calculated magnetic entropy change, ΔS_M, shows an obvious decrease with a broader peak. The origin of the magnetocaloric effect in Dy(Co_1−xFe_x)₂ alloys has been discussed.     

Enhancement of magnetoresistances at room temperature in YSZ doping La0.67Sr0.33MnO3 system

The temperature dependence of the resistance of composite samples (1−x)La_0.67Sr_0.33MnO₃+xYSZ with different YSZ doping level x was investigated at magnetic fields 0-3 T, where YSZ represents yttria-stabilized zirconia. Results show that the YSZ dopant does not only adjust the metal-insulator transition temperature, but also increases the magnetoresistance effect. With increase of YSZ doping level for the range of x<2%, the metal-insulator transition temperature values T_P of the composites decrease, but T_P increases with increase of x further for the range of x>2%. Meanwhile, in the YSZ-doped composites, a broad metal-insulator transition temperature region was found at zero and low magnetic field, which results in an obvious enhanced magnetoresistance in the temperature range 10-350 K. Specially, a larger magnetoresistance value was observed at room temperature at 3 T, which is encouraging with regard to the potential application of magnetoresistance materials.     

Oscillations in magnetocaloric effect and magnetic properties of RE2Al3Si2 (for RE=Dy,Ho and Er) and REAlSi (for RE=Ce and Pr)

We present the magnetic and thermal properties of a series of compounds RE₂Al₃Si₂ for RE=Dy, Ho, Er, and REAlSi for RE=Pr, Ce. The 2–3–2 family crystallizes with themonoclinic Y₂Al₃Si₂-type structure while the 1–1–1 family crystallizes in the body-centered tetragonal α-ThSi₂-type structure. The measurements were done on single crystals, grown using high-temperature flux technique and molten Al as a solvent . Susceptibility and heat capacity data were taken from 1.8 to 200 K, from the heat capacity data, the isothermal magnetic entropy change was obtained. Our results indicate signal oscillations in magnetocaloric properties for those compounds, in particular, Dy₂Al₃Si₂ that shows an anomaly that can be associated with a spin reorientation. Similar results are known for some Dy discilicides and dialluminades.     

Effect of Gd and Fe doping on magnetic properties of Al87Y5Ni8 amorphous alloy

In this paper we present and discuss magnetic properties of the Al₈₇Y₅Ni₈, Al₈₇Y₄Gd₁Ni₈, Al₈₇Gd₅Ni₈, Al₈₇Y₄Gd₁Ni₄Fe₄ and Al₈₇Gd₅Ni₄Fe₄ amorphous alloys. The examinations have been concentrated on a possible magnetic ordering at low temperatures and its modification by amorphous surroundings as well as different magnetic moment of alloying additions. It was shown that magnetic properties of the Al₈₇Y₅Ni₈ amorphous base alloy correspond to a superparamagnetic body with Ni magnetic clusters. Magnetic moment of Ni atom in amorphous aluminum matrix is found to be 0.3 μ_B that corresponds to less than 50 Ni atoms per one cluster. Gd doping of the base alloy leads to a decrease of the resultant magnetic moment of Ni clusters that can be explained by some antiferromagnetic coupling Ni-Gd and Ni-Ni within magnetic clusters.     

Crystal structure and magnetic properties of TbFe0.4Ge2 compound

Neutron diffraction and magnetic measurements were performed on polycrystalline TbFe_0.4Ge₂ which crystallizes with the orthorhombic structure of the CeNiSi₂-type. Despite the presence of some clear anomalies in the low-temperature magnetic susceptibility, the neutron diffraction experiment did not reveal any long-range magnetic ordering of the Tb magnetic moments down to 1.57 K.     

Preparation and characterisation of the double perovskite Sr2TaMnO6

The presented compound, Sr₂TaMnO₆, has a weak, disordered magnetic structure. The metal oxide was prepared under high isostatic oxygen pressure. The doubling of the perovskite structure was proven with electron diffraction and powder neutron diffraction. Combining neutron- and X-ray diffraction data, the room-temperature structure was modelled with the Rietveld method. Both octahedral positions are partially occupied by Mn and Ta, but with different Mn/Ta ratios. AC- and DC-magnetic measurements indicate a magnetic transition at about 17 K and the AC-magnetic susceptibility, both real and imaginary part, is frequency dependent, suggesting that the material has a spin-glass feature. The magnetic spins freeze during a wide temperature range and a possible explanation is a competative situation between the double exchange (ferromagnetism) and the super-exchange (anti-ferromagnetism).     

AC susceptibility and intergranular critical current density study in pure and Ag doped (La1−xYx)2Ba2CaCu5Oz superconductors

The temperature and AC field amplitude variations of AC susceptibility have been measured on pure and 5 wt% Ag doped (La_1−xY_x)₂Ba₂CaCu₅O_z superconductors. The AC susceptibility as a function of field have been analyzed using Kim's critical state model. The temperature dependence of intergranular critical current density and the effective volume fractions of the grains have been estimated. The Ag doped samples show relatively large critical current density due to the improved intergranular coupling. The exponent of temperature variation of critical current density suggests that the weak links form superconductor-normal metal-superconductor (SNS) type of junctions for all the samples.     

Tailoring the magnetic properties of manganese ferrite with substitution of a small fraction dysprosium for iron

Manganese ferrite nanoparticles with dysprosium (Dy) ions substituted for iron ions have been prepared by using a sol-gel method. Substitution of a small fraction Dy for Fe results in the larger magnetocrystallite anisotropy of MnFe_2−xDy_xO₄ (x=0.2, 0.4) nanoparticles than that of MnFe₂O₄ nanoparticles. The magnetosrystallite anisotropy was enhanced with the increase in the substituted dysprosium content. Combining the result of Mössbauer spectra with ZFC and FC curves, we know clearly that the Dy substitution can modify the anisotropy of MnFe₂O₄ nanoparticles for its strong spin-orbital coupling. Through this simple substitution, we can control the magnetosrystallite anisotropy of the magnetic nanoparticles and make good use of the products according as we need.     

Structural,magnetic and electrical properties of Co1−xZnxFe2O4 synthesized by co-precipitation method

Nanoparticles of Co_1−xZn_xFe₂O₄ with stoichiometric proportion (x) varying from 0.0 to 0.6 were prepared by the chemical co-precipitation method. The samples were sintered at 600 °C for 2 h and were characterized by X-ray diffraction (XRD), low field AC magnetic susceptibility, DC electrical resistivity and dielectric constant measurements. From the analysis of XRD patterns, the nanocrystalline ferrite had been obtained at pH=12.5–13 and reaction time of 45 min. The particle size was calculated from the most intense peak (3 1 1) using the Scherrer formula. The size of precipitated particles lies within the range 12–16 nm, obtained at reaction temperature of 70 °C. The Curie temperature was obtained from AC magnetic susceptibility measurements in the range 77–850 K. It is observed that Curie temperature decreases with the increase of Zn concentration. DC electrical resistivity measurements were carried out by two-probe method from 370 to 580 K. Temperature-dependent DC electrical resistivity decreases with increase in temperature ensuring the semiconductor nature of the samples. DC electrical resistivity results are discussed in terms of polaron hopping model. Activation energy calculated from the DC electrical resistivity versus temperature for all the samples ranges from 0.658 to 0.849 eV. The drift mobility increases by increasing temperature due to decrease in DC electrical resisitivity. The dielectric constants are studied as a function of frequency in the range 100 Hz–1 MHz at room temperature. The dielectric constant decreases with increasing frequency for all the samples and follow the Maxwell–Wagner's interfacial polarization.