Magnetic specific heat and magnetoresistance of URhSi

Specific heat of a single crystalline URhSi was measured by a relaxation method in a temperature range 0.3–25 K in magnetic fields up to 8 T applied along the two of the principal axes. The low-temperature specific heat exponentially decays with magnetic field. The decay is much faster in fields applied along the easy magnetization direction (the c-axis) than for the hard axis (the a-axis) case. A strong upturn in c_p/T versus T below 0.6 K that disappears with application of magnetic field is observed suggesting possible magnetic or superconducting phase transition at lower temperatures. The electrical resistivity in the vicinity of the ferromagnetic phase temperature is found to be reduced by more than 50% upon application of magnetic field of 8 T applied along the c-axis. URhSi represent an itinerant ferromagnetic system with influence of spin fluctuations.     

High-field magnetization process in Mn1.9Cr0.1Sb

The compound Mn_1.9Cr_0.1Sb shows a first-order transition from the ferrimagnetic (FI) to the antiferromagnetic (AF) state at T₁ = 265 K with decreasing temperature. High magnetic fields (up to 60 T) produce AF-FI transitions below T_t. The temperature dependence of the critical field is nonlinear and shows T² character at low temperatures (T < 150 K), in contrast to the exchange inversion model of Kittel. This behavior is connected with the itinerant magnetism of 3d-electrons of Mn atoms resulting in a large electronic contribution to the change in free energy at the field-induced first-order AF-FI transition. The field-induced phase transition from the AF to the FI state is accompanied by an increase in the electronic specific heat coefficient γ by 13 mJ K⁻² mol⁻¹ as estimated from the magnetization measurements using thermodynamic relation.     

Grain size dependent magnetization, electrical resistivity and magnetoresistance in mechanically milled La0.67Sr0.33MnO3

We have studied magnetization, ac susceptibility, resistivity and magnetoresistance in mechanically milled La_0.67Sr_0.33MnO₃. The material with grain size micron to nanometer scale has stabilized in rhombohedral crystal structure with space group R3C. We have found various grain size effects, e.g., decrease of ferromagnetic moment, increase of surface spin disorder, and appearance of insulator/semiconductor type resistivity. In addition to these conventional features, we have identified a magnetic anomaly at 45 K in bulk sample. Ferromagnetic to paramagnetic transition temperature (T_C) is above room temperature for all samples. The samples are typical soft ferromagnet that transformed from multi-domain state to single domain state in nanocrystalline samples. The remarkable observation is that low temperature freezing of ferromagnetic domains/clusters does not follow the conventional spin glass features. Experimental results clearly showed the enhancement of high field magnetoresistance in nanocrystalline samples below 200 K, whereas low field magnetoresistance gradually decreases above 200 K and almost absent at 300 K. We have discussed few more magnetic and electrical changes, highly relevant to the progress of nanomaterial research in ferromagnetic manganites.     

Magnetism in PrRhSn studied on a single crystal

We have grown a single crystal of PrRhSn, analyzed the structure by X-ray diffraction methods and measured the specific heat, ac susceptibility, magnetization, and electrical resistivity as functions of temperature and magnetic field. Also we have calculated the electronic structure of this compound by ab initio methods. Ferromagnetism below T_C = 2.9 K characterized by strong uniaxial anisotropy (an anisotropy field 65 T) has been confirmed. Pronounced crystal field (CF) effects were observed on the temperature dependences of the magnetic susceptibility, electrical resistivity and specific heat. The calculations revealed that besides the stable Pr magnetic moment owing to the localized 4f-electrons a small magnetic moment of at most 0.2μ_B is induced at the Rh site (and 0.1μ_B at the Sn site) due to the polarized Rh 4d-electron states (Sn 5p-states) hybridizing with the Pr 5d-electron states, i.e. the Rh and Sn moments play some role in the total balance of the magnetic moments in this compound. This result is in agreement with the experimentally determined saturated magnetic moment of PrRhSn, which is about 0.3μ_B larger than the ordered moment value expected for the Pr³⁺ free ion.     

Step-like and first-order characters of Tb0.2Pr0.8(Fe0.4Co0.6)1.93 with low interstitial carbon content

In this study we report detailed magnetic property of the 4f-3d pseudo-quaternary Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.88C_0.05 compound by detailed magnetization measurements. Very sharp magnetization jumps across the antiferromagnetic–ferromagnetic transition are observed below 3.0 K, and the number of jump-like transitions increases with decreasing temperature. The time-dependent magnetic relaxation, field sweep rate and cooling field dependence of magnetization jumps resemble the martensitic scenario. The number and occurrence of magnetization jumps are mainly determined by the competitions between the thermal fluctuation energy, elastic energy and Zeeman energy, and the field-induced antiferromagnetic to ferromagnetic phase transition at low temperatures is of first-order in nature.     

Effect of parameters of heat treatment on magnetic properties and magnetization distribution in ribbons of amorphous soft magnetic iron-based alloys

The effect of the isothermal-holding temperature and cooling rate upon in-air heat treatment on the magnetic properties and magnetization distribution in ribbons of amorphous soft magnetic iron-based alloys with positive saturation magnetostriction has been investigated. The results of the investigation showed that the dependence of the maximum magnetic permeability on the isothermal-holding temperature correlates with the corresponding changes in the magnetization distribution in the ribbon and is determined by diffusion processes that occur upon in-air heat treatment at a specific isothermal-holding temperature. An increase in the cooling rate leads to an ambiguous effect on the level of magnetic properties. The increase favors an improvement in magnetic properties when, after in-air heat treatment, either a predominantly amorphous state of the surface or a state with the formed amorphous-crystalline surface layer with a nearly optimal thickness is obtained.     

USb2单晶的生长及磁性和输运性质研究

采用Sb自助熔剂法成功生长高质量的USb₂单晶,并研究了磁化率、电阻、磁阻和比热等性质。研究表明,中等关联强度的USb₂中的5f电子具有巡游和局域双重特征。USb₂中的5f电子在260 K附近开始发生相干,203 K由顺磁态转变为反铁磁态,进行费米面的重构。在113 K以下局域的5f电子与传导电子发生第一次杂化使费米面附近电子结构发生变化。在54 K以下通过第二次杂化使得费米面附近形成了杂化能隙。在更低温度下晶体场效应对物理性质也产生了一定的影响。     

Influence of grain size on magnetic and transport properties of polycrystalline La0.8Sr0.2MnO3 manganites

In this study, we have investigated the effects of grain size on the magnetic and transport properties of polycrystalline La_0.8Sr_0.2MnO₃ samples. The samples were prepared by solid-state reaction method. In order to obtain a series of samples with different grain sizes, the bulk sample was subjected to high energy ball milling. The magnetization decreases by decreasing grain size. A decrease in magnetization by decreasing grain size is due to the increasing of magnetically disordered states at the surface of grains. By decreasing the grain size the resistivity increases and a second peak was observed at temperatures well bellow T_c. The intrinsic CMR decreases by decreasing grain size while the extrinsic intergranular MR is promoted to larger values. A model, proposed by Zhang et al. [N. Zhang, W. Ding, W. Zhong, D. Xing, Y. Du, Phys. Rev. B 56 (1997) p. 8138.], involving domain walls contribution and a spin polarized tunneling between neighboring grains of manganites below transition temperature may be responsible for this behavior.     

Magnetic and electrical properties of the UCu2T3Al7 alloys

The UCu₂T₃Al₇-type compounds with T = Cr, Mn and Fe crystallize in the tetragonal ThMn₁₂-type structure (I4/mmm space group). Magnetic properties have been examined in magnetic fields up to 50 kOe in the temperature range 1.9–400 K using a SQUID magnetometer. The Cr based pseudoternary alloy is paramagnetic with the linear field dependence of the magnetization at 1.9 K. The temperature dependence of the magnetic susceptibility is described by a modified Curie–Weiss (MCW) law. The Mn containing compound is ferrimagnetic and the field dependence of the magnetization does not reach saturation while the magnetic susceptibility follows the MCW law at high temperature. The Fe alloy is ferromagnetic and at higher temperature the MCW law is fulfilled. The temperature dependence of the electrical resistivity of all materials was examined between 4.2 and 300 K showing metallic character. The Mn and Fe based compounds demonstrate some anomalies in the ρ(T) plot at low temperature. The results are discussed in relation to the anomalies observed in magnetic measurements.     

Magnetic and related properties of Ce5CoGe2, CeCoGe and CeCo2Ge2

Magnetic susceptibility, magnetization, specific heat, electrical resistivity and thermoelectric power of polycrystalline Ce₅CoGe₂, CeCoGe and CeCo₂Ge₂ were studied at temperatures down to 2 K and in magnetic fields up to 5 T. The novel phase Ce₅CoGe₂ was found to be a ferromagnet with the Curie temperature of about 11 K, which exhibits in the paramagnetic region some features of a dense Kondo system with strong crystal field effect. The re-investigated CeCoGe was found to order antiferromagnetically below 4.6 K, while CeCo₂Ge₂ is an intermediate-valence system, in agreement with previous reports. The thermoelectric power of the latter compound is large (up to 40 μV/K) and positive in the whole temperature range studied, while in the magnetically ordered systems Ce₅CoGe₂ and CeCoGe it is mostly negative and distinctly smaller (down to −1.5 and −11 μV/K, respectively).     

Effects of ferrites on magnetic transport properties in La2/3Sr1/3MnO3/ferrites composites

Effects of soft-magnetic MnZn ferrite (Mn0.5Zn0.5Fe2O4, MZF) and hard-magnetic Ba ferrite (BaO·6Fe2O3, BaM) on the structure and magnetic transport properties of [La2/3Sr1/3MnO3] (LSMO)/(x) [ferrites] (ferrites=MZF, BaM) composites have been investigated. It was found that the inclusion of MZF phase reduces magnetization and ferromagnetic-paramagnetic transition temperature (Tc) of the composites. With increasing the content of the dopants, the high-temperature magnetoresistance (MR) decreases, whereas low-...     

Magnetic characterization of polycrystalline NdFeAsO0.88F0.12 oxypnictide superconductor

The superconducting properties of polycrystalline NdFeAsO_0.88F_0.12 oxypnictide were studied by both DC and AC magnetization measurements. The zero-field cooled (ZFC) magnetic susceptibility, χ(T), measured under the magnetic field of 0.5 T shows a dramatic decrease at about 11 K. The imaginary component of the first harmonics of the AC magnetic susceptibility, χ″(T), increases with the increasing DC field H_dc below 11 K. These results indicate the onset of robust intergranular superconductivity at low temperatures. The magnetic hysteresis loops show an anomalous double central peak effect at low temperatures, with one peak at positive fields in decreasing positive external fields. This phenomenon suggests the granular character of this system. The paramagnetism of Nd³⁺ ions tilts the magnetic hysteresis loops and broadens the hysteresis width ΔM. After correction for the paramagnetism, the temperature and field dependence of the average magnetization critical current density J_cm was obtained. The related mechanism was discussed.     

Electrical and magnetic properties of NdCuPb compound

Electrical and magnetic properties of NdCuPb compound were investigated by means of electrical resistivity, magnetization measurements in the temperature range 1.5–100 K. Low-field dc susceptibility goes through a maximum at T_N=13.2  K, indicating a paramagnetic to an antiferromagnetic transition and then follows a sharp peak at T=5.9  K. The susceptibility data exhibits a Curie–Weiss like behavior in the paramagnetic regime and the effective moment per neodium atom is found to be 3.62μ_B from the data at temperatures above 42 K. This value is exactly equal to that for Nd³⁺, while at lower temperatures, the data yields a little bit less than its free ion value. The ratio M/H versus temperature T curves for different values of the magnetic field split into multiple branches at about T=42  K due to crystalline field effects.In addition, electrical resistivity in a magnetic field up to 120 kOe was also measured in the same temperature range. The resistivity gives non-metallic behavior. The antiferromagnetic transition is clearly discern by a “Cr-like” anomaly at about 13 K, followed by a sharp increase in the resistivity (like a jump) at T=5.9  K where the susceptibility gives similar effect. On other hand, the magnetic contribution to the resistivity begins to decrease at T=42  K at which M/H curves merges. All these behavior may be attributed to crystal-field-splitting of neodium atoms’levels.     

Influence of cooling field on the magnetic properties of Ni/NiO nanostructure

Nanoparticles of Ni/NiO structure were prepared by sol–gel route followed by the annealing in presence of controlled oxygen and argon gas mixture. When the sample was cooled down to 5 K from room temperature in a static magnetic field, a systematic shift of the magnetic hysteresis loop was observed. The shift was absent when the sample was cooled in zero field. For cooling the sample in field-cooled mode a small horizontal shift was noticed along with a moderate vertical shift of the hysteresis loop at the saturation of magnetization, which indicates the typical manifestation of exchange bias effect. The horizontal shift increases with decreasing particle size retaining almost unchanged relative vertical shift, where vertical shift is found to be uncorrelated with the horizontal shift. The exchange bias like effect in the Ni/NiO nanostructure is suggested at the Ni/NiO interface, where Ni is ferromagnetic and NiO is in the disordered magnetic state.     

Synthesis and magnetic properties of NdMnAl and some RMnIn (R=rare earth)

The equiatomic ternary compounds NdMnAl and RMnIn (R=Nd, Gd, Dy, Er, and Y) have been synthesized for the first time. In this paper, we report their crystal structure and the magnetic behavior of three of them (i.e., NdMnAl, GdMnIn, and DyMnIn). While NdMnAl and NdMnIn have the cubic, Laves-phase, C-15-type structure, the latter compounds form in the closely related hexagonal, Laves-phase, C-14-type structure. The Mn ions carry a substantial magnetic moment in the three compounds, but magnetization does not exhibit signatures of long-range magnetic ordering. Broad peaks in the thermal variation of magnetization, accompanied with thermomagnetic irreversibility below the peak region and hysteresis loops at low temperatures with large coercivity indicate spin glass-type freezing of the magnetic moments. The heat capacity data, measured in the range of 1.8 to 100 K, do not exhibit peaks associated with long-range magnetic order and, thus, corroborate the results inferred from magnetization data. Resistivities of these compounds are large and show negative temperature coefficients. These observations can be reconciled to a highly disordered state brought about by the random substitution of In or Al for Mn in these compounds.     

Synthesis and magnetic properties of NdMnAl and some RMnIn (R=rare earth)

The equiatomic ternary compounds NdMnAl and RMnIn (R=Nd, Gd, Dy, Er, and Y) have been synthesized for the first time. In this paper, we report their crystal structure and the magnetic behavior of three of them (i.e., NdMnAl, GdMnIn, and DyMnIn). While NdMnAl and NdMnIn have the cubic, Laves-phase, C-15-type structure, the latter compounds form in the closely related hexagonal, Laves-phase, C-14-type structure. The Mn ions carry a substantial magnetic moment in the three compounds, but magnetization does not exhibit signatures of long-range magnetic ordering. Broad peaks in the thermal variation of magnetization, accompanied with thermomagnetic irreversibility below the peak region and hysteresis loops at low temperatures with large coercivity indicate spin glass-type freezing of the magnetic moments. The heat capacity data, measured in the range of 1.8 to 100 K, do not exhibit peaks associated with long-range magnetic order and, thus, corroborate the results inferred from magnetization data. Resistivities of these compounds are large and show negative temperature coefficients. These observations can be reconciled to a highly disordered state brought about by the random substitution of In or Al for Mn in these compounds.     

Magnetic and electrical properties of RCu5.1In6.9 compounds

Magnetic and electrical properties of the RCu_5.1In_6.9 compounds with R=Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er were investigated in the temperature range 4.2–300 K. Additionally, for the compounds of Gd, Tb and Dy exhibiting magnetic anomalies at low temperatures, the magnetization versus magnetic field up to 14 T was measured at 4.2 K. Investigated compounds follow the Curie–Weiss law with relatively small values of the paramagnetic Curie temperature and the values of effective magnetic moment being in fair agreement with the values for the free ions. The electrical resistivity exhibits metallic character. The results are discussed in terms of the differences and similarities with other rare earth intermetallics.     

Revisiting the superconducting phase diagram of(TMTSF)2ClO4

We present results of a search for evidence of reentrance at high magnetic field of the superconducting state in the quasi-one dimensional organic superconductor (TMTSF)₂ClO₄, for a specific orientation of the field at low temperature. This search was motivated by the theoretical work of Lebed' and of Dupuis and Montambaux, and in part by that of Te anovic and coworkers, who predict novel magnetic field-temperature phase diagrams in quasi-1-D and quasi-2-D superconductors in a strong magnetic field. In the quasi-1-D case, a field directed both normal to the chains and along the layers is proposed to induce exotic oscillations of the critical temperature at high field, while for the 2-D case, quantum effects associated with Landau quantization lead to similar predictions. We have investigated the superconducting transition in a quasi-1-D candidate material, (TMTSF)₂ClO₄, to 0.06 K with field oriented along the b′-axis (± 0.02°). From mostly constant field temperature sweeps, we find positive curvature in H_c2(T) below about T_c/2. In addition, a resistivity decrease is observed to persist to 7 T, the highest field employed, with a slightly positive slope ∂H/∂T above 5T. The possibility of these features being representative of high field superconductivity is discussed.     

Magnetic properties of ErMn2 single crystals

Single crystals of the ErMn₂ compound were grown by the Czochralski method from a levitated melt. The thermal dependence of the lattice parameters exhibits a magnetovolume effect along the a axis, a contraction for both the c axis and unit cell volume below 20 K. The thermal dependence of the electrical resistivity exhibits a magnetic transition at 23 K. A second transition occurs at 13 K. Moreover, for ρ(T) a negative curvature above the ordering temperature and a saturation effect above 200 K occurs. The magnetization in strong magnetic fields, the d.c. and a.c. magnetic susceptibilities measured along the principal crystallographic directions show ordering of the erbium moments to a spin-canted magnetic structure at about 15 K and a spin reorientation about 10 K.     

Antiferromagnetic ordering below 1.7 K in PrIr2Ge2

We present our investigations on magnetic and transport properties of polycrystalline PrIr₂Ge₂ which forms in CaBe₂Ge₂-type primitive tetragonal structure (space group P4/nmm). The ac magnetic susceptibility data exhibit two well pronounced peaks at 2.08 K and 0.76 K due to the onset of magnetic order. The specific heat also exhibits a sharp λ-type anomaly at 1.7 K confirming the onset of bulk antiferromagnetic order. The temperature dependence of magnetic part of entropy suggests a quasi-triplet ground state in this compound. The onset of magnetic order is also confirmed by the electrical resistivity data.