Comparison of the Magnetic Ordering in Sr2Yb1Ru0.9Cu0.1O6 and Ru1Sr2Gd1Cu2O8 Superconductors

Ru₁Sr₂Gd₁Cu₂O₈ and Sr₂Yb₁Ru_0.9Cu_0.1O₆ were synthesized using a solid-state reaction. X-ray diffraction showed that Ru₁Sr₂Gd₁Cu₂O₈ crystallized into the tetragonal Ru-1212 structure (space group P4/mmm), whereas the Sr₂Yb₁Ru_0.9Cu_0.1O₆ had a monoclynic structure (space group P2₁/n). Sr₂Yb₁Ru_0.9Cu_0.1O₆ showed a possible magnetic transition ( T _{m a g} ) at 44 K with a superconducting transition temperature T _c at 30 K. In contrast, Ru₁Sr₂Gd₁Cu₂O₈ showed a magnetic transition at 140 K with a T _c at 25 K. The magnetization data for Sr₂Yb₁Ru_0.9Cu_0.1O₆ suggests that this sample exhibits antiferromagnetic ordering in zero-field-cooled (ZFC) magnetization, whereas it reveals a weak ferromagnetic component during field-cooled (FC) cycles. In addition, larger diamagnetic signals were observed during FC cycle compared to the ZFC. These results suggest that the valence state of the Yb ion have a significant effect on the magnetic state of the Sr₂Yb₁Ru_0.9Cu_0.1O₆ superconductor.     

Magnetic properties of RRh3B2(R=La,Ce, Nd,Gd) compounds

The¹¹Bnmr results on RRh₃B₂(R=La, Ce, Nd and Gd) are reported. For CeRh₃B₂, specific heat and electrical resistivity are reported. From a comparative study of the¹¹Bnmr Knight shifts and the spin lattice relaxation times of these compounds it is shown that in CeRh₃B₂, there is strong hybridization of 4f states with the conduction electrons. A local moment on Ce with admixture of 4f and 5d–6s orbitals is suggested.     

Superconductivity and Magnetism in R 2CaBa2Cu5O z (R=La, Pr, Nd and Eu)

A series of compounds R ₂CaBa₂Cu₅O _z (R=La, Pr, Nd and Eu) have been synthesized by conventional solid state reaction and characterized for their structural, superconducting and magnetic properties. All compounds crystallize with the tetragonal LaBa₂Cu₃O _z type structure, space group P4/mmm. Among the four compounds studied here, R=La, Nd and Eu are superconductors with superconducting transition temperatures (T _c ^R=0) of 72, 40 and 55 K, respectively. On the other hand, neither superconductivity nor magnetic ordering is seen for R=Pr down to 3 K. The effect of the magnetic field on the susceptibility and (magneto) resistance for the superconducting samples has been investigated. The superconductivity of compounds with magnetic rare-earth ions Nd and Eu exhibit a profound influence of the magnetic field, whereas the application of the magnetic field has a limited effect on the La compound. The Pr compound is paramagnetic and does not exhibit magnetic ordering either.     

Magnetic Properties of RB66 (R = Gd, Tb, Ho, Er, and Lu)

We report magnetic susceptibility measurements of RB₆₆ (R = Gd, Tb, Ho, Er, and Lu) boron-rich rare earth containing borides down to 50?mK. The data suggest a spin glass low temperature state for RB₆₆ (R = Gd, Tb, Ho, and Er) with the freezing temperatures below 1?K. The magnetic properties appear to be influenced by the anisotropy of the magnetic moments, probably via the crystalline electric field effects.     

Superconductivity and Ferromagnetism of the Ru-1232 Compounds in the (Ru1−x Nb x )Sr2(GdCe1.8Sr0.2)Cu2O z System

The Ru-1232 compounds have been synthesized in the (Ru_1?xNb _x )Sr₂(GdCe_1.8Sr_0.2)Cu₂O _z system, and effects of Nb substitution for Ru on superconductivity and ferromagnetism of the Ru-1232 compounds have been investigated. First, X-ray powder diffraction study shows that nearly the single 1232 phase samples can be obtained in the x composition range from 0.0 to 0.3. Then, from the electrical resistivity study, it is found that each of the samples shows resistivity dropping phenomenon at two temperatures of T _c ^l and T _c ^h, which originates from superconductivity of the Ru-1232 phase and the Ru-1222 one, respectively. Both of the starting temperatures are lowering with increasing Nb content x. Lastly, from the magnetic susceptibility study, it is found that superconducting transition temperature T _c is 20 K for the Ru-1232 sample with x = 0.0 and the ferromagnetic transition temperature T _m is about 90 K. This study also shows that both of the values of T _c and T _m become low with increasing x from 0.0 to 0.3.     

Synthesis of New Pb-based 1222 Layered Cuprates in the (Pb,S)Sr2(RE,Ce)2Cu2O z (RE=Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Y) System

A new family of the Pb-based layered cuprate with the 1222 structure has been synthesized in the (Pb,S)Sr₂(RE,Ce)₂Cu₂O _z (RE=Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Y) system. The almost-single phase samples are obtained for x=0.25 and y=1.0 in the composition of (Pb_1?x S _x )Sr₂(RE_2?y Ce _y )Cu₂O _z . Each of the samples has the crystal structure with a tetragonal symmetry. Both of the lattice parameters a and c are decreasing with the decrease of the ionic radius of RE element. Among these samples, the sample with RE=Er has the smallest resistivity in the whole temperature range and the slope of the resistivity versus temperature is the most gentle. Despite annealing under O₂ atmosphere at high-pressure of 121 atm, this sample is a semiconductor with the transport process characteristics of three-dimensional variable range hopping conduction. Then the samples of RE=Er with smaller y are investigated for the composition of (Pb_0.75S_0.25)Sr₂(RE_2?y Ce _y )Cu₂O _z , the sample with y=0.4 is found to show an onset of resistivity drop phenomenon at about 11 K with the decrease of temperature. Moreover, we also discover that the samples of RE=Ho with y=0.4 show an onset of the resistivity dropping at over 20 K and zero resistivity at 13 K. From these results, the present (Pb_0.75S_0.25)Sr₂(RE_2?y Ce _y )Cu₂O _z system is considered to be a new family of the Pb-based superconducting cuprates with the 1222 structure.     

Anomalous Magnetic Behavior in RuSr2(Gd2−x Ce x )Cu2O10

We studied the magnetic properties of RuSr₂(Gd_2–x Ce _x )Cu₂O₁₀. In the temperature dependence of magnetic susceptibility, we observed a ferromagnetic increase and an anomalous oscillating behavior below T _M. In ESR measurements, we observed a single magnetic resonance signal from Ru ions and a similar wavy structure in its resonance field below T _M. These magnetic phenomena possibly originate from an intrinsic Ru-spin motion.     

Structural, Magnetic, and Magnetocaloric Properties of La0.5M0.1Sr0.4MnO3 (M=Bi, Eu, Gd, and Dy) Perovskite Manganites

Structural, magnetic, and magnetocaloric properties of La_0.5M_0.1Sr_0.4MnO₃ (M=Bi, Eu, Gd, and Dy) powder samples, synthesized using the solid-state reaction at high temperature, have been experimentally investigated. X-ray diffraction analysis using the Rietveld refinement show that La_0.5Bi_0.1Sr_0.4MnO₃ sample is single phase and crystallizes in the rhombohedral system with $R\overline{3}c$ space group whereas a mixture of orthorhombic (Pbnm) and rhombohedral ( $R\overline{3}c$ ) phases is observed for M=Eu, Gd, and Dy compounds. The Curie temperature, T _C , shifts to lower temperature with decreasing the average A-site ionic radius 〈r _A 〉, which is consistent with large cationic disorder. Arrott plots show that all our samples exhibit a second order magnetic phase transition. From the measured magnetization data of La_0.5M_0.1Sr_0.4MnO₃ (M=Bi, Eu, Gd, and Dy) samples as a function of magnetic applied field, the associated magnetic entropy change |ΔS _M | has been determined. In the vicinity of T _C , |ΔS _M | reached, in a magnetic applied field of 1 T, maximum values of 0.98 J/kg?K, 1.01 J/kg?K, 0.81 J/kg?K, and 0.77 J/kg?K for M=Bi, Eu, Gd, and Dy, respectively.     

Structural and Magnetic Properties of YBa2Ru0.85Cu0.15O6 and Sr2Re0.69Ca0.31CuO6 Perovskites

In this present investigation, both YBa₂Ru_0.85Cu_0.15O₆ and Sr₂Re_0.69Ca_0.31CuO₆ perovskite compounds were prepared through high pressure/high temperature (HPHT) synthetic route. The as-prepared samples were structurally characterized by powder X-ray diffraction technique and their magnetic properties were measured. Both compounds crystallized in cubic symmetry with a different space group. The refined lattice parameter for the YBa₂Ru_0.85Cu_0.15O₆ and Sr₂Re_0.69Ca_0.31CuO₆ compounds are found to be a=8.332(2) ? with space group, Fm-3m (225) and a=7.967(4) ? space group Pm-3m (221), respectively. The cuprate ordered perovskite compound shows ferromagnetism with high Curie temperature, T _c at ∼450 K whereas the YBa₂Ru_0.85Cu_0.15O₆ compound reveals mixed magnetic natures below ∼170 K which is complicated by the presence of magnetic order in the Ru and Cu sublattices. Below 170 K, the compound shows two antiferromagnetic-like transitions (in ZFC mode) at ∼135 K and ∼60 K. With a further decrease of temperature (below 60 K), the susceptibility crosses negative (diamagnetic) signal at ∼35 K and shows maximum negative susceptibility at ∼11 K. By decreasing the temperature below 11 K, the negative susceptibility decreases and shows positive magnetic susceptibility at 2 K. In the fc mode curve, the sample shows broad antiferromagnetic like transition at ∼55 K. At low temperature (below 30 K), an increase in susceptibility signal is seen in the fc magnetic susceptibility curve. The magnetic parameters, such as Weiss temperature, θ _w and the effective paramagnetic moment, p_eff obtained from the linear region of χ ⁻¹(T) plots are found to be −307.25 K and 3.74 μ _B/Ru, respectively, for the YBa₂Ru_0.85Cu_0.15O₆ compound. The negative sign of θ _w reveals the antiferromagnetic correlations of the compound. While these studied compounds are already known to the literature, the synthesis method (HPHT) employed for the present YBa₂Ru_0.85Cu_0.15O₆ compound is a new approach and quite different from the routine conventional solid state synthesis approach.     

Formation of high-T c Bi1.6Pb0.4Sr2Ca2(Cu0.9Ti0.1)3O x

Influences of sintering conditions onT _c are studied for Bi_1.6Pb_0.4Sr₂Ca₂(Cu_0.9Ti_0.1)₃O _x . HighT _c values are obtained at 1123±5 K sintering temperature and over 50 h sintering time. In order to explain theT _c changes, morphological discussion is attempted.     

Nd0.67(Sr,Ca)0.33Mn(O,F)3磁电阻材料的结构与性能

通过掺CaF2制得了Nd0.67(Sr,Ca)0.33Mn(O,F)3 (NSMO)磁电阻材料,并对它们作了结构分析和磁性能测量. X射线衍射结果表明,NSMO化合物保持Nd0.67Sr0.33MnO3的钙钛矿结构,空间群为Pbnm,Z=4,F-离子占据8d位置,随着CaF2掺入量的增加,晶格常数减小,居里温度降低,而磁电阻性质呈明显的递增趋势. 当掺入量为20mol%时, ΔR/R(0)的峰值达到99.7%.     

New Ru-Based Layered Cuprates with 1232 Structure in the RuSr2(LnCe2−x Sr x )Cu2O z (Ln = Sm, Eu, and Gd) System

New Ru-based layered cuprates with 1232 structure have been synthesized in the RuSr₂(LnCe_2?x Sr _x )Cu₂O _z (Ln = Sm, Eu, and Gd) system. Nearly single-phase samples are obtained in the composition range from x = 0.0 to 0.2 for Ln = Sm and Eu, and at the composition of x = 0.2 for Ln = Gd. Each of the samples of Ln = Sm, Eu, and Gd with x = 0.2 crystallizes in a tetragonal lattice and lattice parameters a and c are 0.3845 and 1.700 nm, 0.3842 and 1.699 nm, and then 0.3839 and 1.698 nm, respectively. Each of them shows some anomalies at a low temperature in addition to a semiconductor-like temperature dependence of the resistivity. Especially, the sample with Ln = Gd shows two resistivity dropping phenomena at about 16 and 22 K. Then, all of nearly single-phase samples show diamagnetic signals originating from superconductivity, and also rapid increase of magnetization due to a transition from paramagnetic state to ferromagnetic one below 80 K.     

NiCuZn-Sr(Nb0.5Al0.5)0.1Ti0.9O3磁介复合陶瓷材料的磁介性能研究

现代移动通信技术的高速发展对各类电子设备的小型化、多功能化提出了新的要求.开发性能优良的新型磁介复合材料成为元器件小型化的解决方案之一.本工作采用固相烧结法分别合成了NiCuZn铁氧体材料以及Sr(Nb0.5 Al0.5)0.1 Ti0.9 O3介电材料,然后将两者按照一定比例复合,研究了不同铁氧体/介电相含量对磁介复合陶瓷材料磁性能与介电性能的影响,并对其微观形貌与相结构进行了探究.研究结果表明,当铁氧体含量在0.7～0.8时,复合材料致密性最好,磁性能与介电性能较为优良.     

Low-Temperature Neutron Diffraction and Magnetic Properties of La1.2Sr0.9Ca0.9Mn2O7

The crystal structure and magnetic properties of a typical polycrystalline double-layered manganite, La_1.2Sr_0.9Ca_0.9Mn₂O₇, were examined using neutron diffraction and magnetization techniques. Neutron diffraction was performed at low and room temperatures and the crystal structure was refined using the Rietveld method based on the space group I4/Mmm. Low temperature neutron diffraction and magnetization measurements clearly revealed antiferromagnetic ordering. A neel transition was observed at approximately 150 K.