Influence of Charge Doping on Thermal Diffusivity of Double Perovskite Sr2FeMoO6 Studied by Mirage Effect

Effects of charge doping on thermal diffusivity have been investigated in double perovskite ferromagnetic Sr_2–x La _x FeMoO₆ (0 x 0.4) by means of the mirage effect at 300 K ( the critical temperature T _c 420 K). Substitution of the La³⁺ ions for the Sr²⁺ ions significantly increases the value of the thermal diffusivity from 0.39 cm² · s^–1 at x = 0 to 0.54 cm² · s^–1 at x = 0.4. The increased thermal diffusivity is ascribed to the extra itinerant electrons on the Mo4d band.     

Magnetic Torque Measurements on Bi2201 Single Crystal in High Magnetic Fields

The magnetic field direction dependence of the magnetic torque in the superconducting state of Bi ₂ Sr _1.65 La _0.35 CuO ₆₊ (Bi2201) single crystal has been measured in several static magnetic fields up to 200 kOe. The applied field dependence of the anisotropy parameter, , defined by the square root of the effective mass ratio has been obtained by fitting the magnetic torque curves at 17 K by means of the effective mass model. For Bi ₂ Sr ₂ CaCu ₂ O ₈₊ (Bi2212), the values up to 210 kOe were reported previously. At each field, for Bi2201 is larger than that for Bi2212. Since the value decreases as the field increases both for Bi2201 and Bi2212, the reduction of by the application of the high magnetic field is considered to be common for Bi-based layered superconductors.     

Local Valence and Hole-Doping Effect on Magnetic Properties in Double Perovskite La2NiMnO6

Local valence and Ca-doping effect in polycrystalline La₂NiMnO₆ have been investigated by using X-ray diffraction, X-ray absorption spectroscopy, Raman spectrum, and magnetometry. The refinement of X-ray diffraction data shows that all the samples are crystallized in pure double perovskite phase. The refined Ni(Mn)–O bond lengths and X-ray absorption spectroscopy provide evidences that the oxidation state of Ni and Mn ions in bulk La₂NiMnO₆ has the Ni²⁺ and Mn⁴⁺ configuration and the decrease of average A-site valence caused by Ca doping is compensated by the increase of Ni valence, while Mn keeps unchanged. As the Ca-doping content increases, the peak shapes of Raman spectroscopy exhibit an increase in the linewidth and decrease in the intensity, respectively, which reveals the increase the disorder of Ni–O bond length and the decrease of Ni/Mn ordering degree. Both the paramagnetic–ferromagnetic transition temperature and the saturation magnetization exhibit decrease with the increase of Ca-doping content, which are attributed to the decrease of Ni–O–Mn bond angle and the increase of Ni/Mn antisite disorder, respectively. All those behaviors can be ascribed to the valence state change of Ni ion caused by hole doping.     

Spin polarized itinerant electrons in Ca2FeMoO6 double perovskites

We report on magnetic studies of the double perovskite Ca₂FeMoO₆ in its paramagnetic state. It is found that the effective magnetic moment, extracted from the Curie constant, is magnetic field dependent and it is smaller than that expected in a simple ionic scenario. These experimental results, which are in agreement with early reports on Sr₂FeMoO₆, are interpreted as a direct evidence of the antiferromagnetic coupling and polarization of the conduction band in these oxides. A simple mean field model accounts for these observations and enlightens the relevance of itinerant carriers on the strength of the magnetic coupling in these oxides.     

Magnetic Properties of FeAs Single Crystal

Magnetic measurements have been performed on FeAs single crystals and polycrystalline samples. Magnetic measurements revealed a very sharp spin-glass magnetic transition in self flux grown single crystal. The bifurcation point between zero field cooled (ZFC) and field cooled (FC) magnetization occurs at 130 K. Susceptibility of flux grown single crystals revealed ferromagnetic-type behavior in the temperature range 4–300 K, while single crystals grown by iodine transport vapor were non-magnetic revealed features associated with antiferromagnetic and spin wave characteristics. The shift in Raman lines reveled sharper peaks for the crystals grown by vapor transport method than that obtained for the flux grown crystals. The difference in the spectrum may indicate sharper distribution in the bonding strength between Fe and As ions in crystals grown by the iodine vapor transport method.     

Instability of Structural, Magnetic, and Magnetoresistive Properties in Ordered Double-perovskite Sr_2FeMoO_6 Polycrystals

The problem of instability in polycrystalline ordered double-perovskite Sr2FeMoO6, is presented in this paper. By the X-raydiffraction analysis and the measuring of electrical and magnetic transports, it is indicated that the perovskite structure of thecompound is destroyed, and the Sr2FeMoO6 phase is mainly transformed into SrMo04 phase when the samples are exposedin damp atmosphere for several weeks or immersed in water for several hours. Simultaneously, their electrical and magneticproperties obviously change, and the value of magnetoresistance remarkably reduces and even vanishes at room temperature.A possible micromechanism of the instability and an effective method to avoid the problem of instability are also discussed.     

Effect of ex situ Post-annealing Treatments on Sr2FeMoO6 Thin Films

Magnetoresistive Sr₂FeMoO₆ thin films were grown by pulsed laser deposition at optimized deposition atmosphere and temperature. Films were then ex?situ post-annealed in different atmospheres and by vacuum annealing at temperatures between 500?°C and 1100?°C. Ar and air annealed samples were destroyed by ex?situ post-annealing treatment, due to formation and dominance of SrMoO₄ impurity phase. X-ray diffraction showed no impurities and full texturation of vacuum and ArH₂ (5%) annealed samples. Those samples showed also similar magnetic and magnetoresistive behavior like as-deposited sample. Neither magnetic, magnetotransport nor structural properties could be improved by ex?situ post-annealing treatments.     

High-Field Magnetization Measurements for a Single Crystal of Er2Fe17H3 Hydride

High-field magnetization process of the single crystal of Er₂Fe₁₇H₃ is investigated and compared with that of the parent Er₂Fe₁₇ in order to clarify the effect of interstitial hydrogen on magnetic properties. Substantial change in the magnetic anisotropy behavior observed for Er₂Fe₁₇H₃ is explained by the modification of the interaction between the 4f-shell orbital moment of Er and the crystal field leading to the change of the second-order crystal electric field coefficient $A^{0}_{2}$ . Hydrogenation does not practically affect the intersublattice molecular field.     

Centimeter-Sized Single Crystals of Dion-Jacobson Phase Lead-Free Double Perovskite for Efficient X-ray Detection

2D Dion–Jacobson (DJ) phase hybrid perovskites have shown great promise in the photoelectronic field owing to their outstanding optoelectronic performance and superior structural rigidity. However, DJ phase lead-free double perovskites are still a virgin land with direct X-ray detection. Herein, we have designed and synthesized a new DJ phase lead-free layered double perovskite of (HIS)₂AgSbBr₈ ( 1 , HIS²⁺ = histammonium). Centimeter-sized (18 × 10 × 5 mm³) single crystals of 1 are successfully grown via the temperature cooling technique, exhibiting remarkable semiconductive characteristics such as a high resistivity (2.2 × 10¹¹ Ω cm), a low trap state density (3.56 × 10¹⁰ cm⁻³), and a large mobility-lifetime product (1.72 × 10⁻³ cm² V⁻¹). Strikingly, its single-crystal-based X-ray detector shows a high sensitivity of 223 µC Gy⁻¹_air cm⁻² under 33.3 V mm⁻¹, a low detection limit (84.2 nGy_airs⁻¹) and superior anti-fatigue. As far as we know, we firstly demonstrates the potential of 2D DJ phase lead-free hybrid double perovskite in X-ray detection, showing excellent photoelectric response and operational stability. This work will pave a promising pathway to the innovative application of hybrid perovskites for eco-friendly and efficient X-ray detection.     

Effect of Magnetic (Nd) Doping on Electrical and Magnetic Properties of Topological Sb2Te3 Single Crystal

Journal of Superconductivity and Novel Magnetism - Here, we report the growth and characterization of single crystals of NdxSb2-xTe3 (x?=?0 and 0.1), by solid-state reaction route via...     

Magnetic Anisotropy of PrNi5 Single Crystal at Millikelvins

Magnetic ordering in the hyperfine enhanced nuclear ferromagnet PrNi₅ was investigated in external magnetic fields up to 72 mT at temperatures from below the ordering temperature up to about 20 mK. An anisotropy of the magnetization and ac susceptibility was observed for two single crystalline samples having a or c crystallographic axis parallel to the external field. The results show that the nuclear magnetic moments of Pr are ordered in the basal plane of the hexagonal crystal structure of PrNi₅.     

烧结时间对双钙钛矿Sr_2FeMoO_6晶体结构及微结构的影响

采用高温固相反应法制备了样品Sr_2FeMoO_6,根据烧结时间不同分别记为1,2和3#。采用X射线衍射技术研究了烧结时间对物相的影响,并对其晶体结构进行了分析。X射线衍射结果表明烧结时间的增加能有效提高晶体的结晶性和阳离子有序度,其1,2和3#样品的Fe/Mo阳离子有序度分别为90.0(2)%,94.0(5)%和95.3(4)%。采用扫描电子显微镜对该系列样品的微结构进行分析,结果表明随着烧结时间的增加,晶粒越来越大,空洞逐渐减少,晶界越来越清晰,晶粒尺寸越来越均匀。采用粒径分布计算软件对3个样品的粒径进行分析,得到1,2和3#样品的粒径分别为0.97,1.12和1.58μm。     

Resistivity Studies by Multiterminal Transport Measurements on Single Crystal YBa2Cu3O7−δ

Multiterminal transport studies provide a powerful technique to investigate vortex structure and correlations in the vicinity of the vortex solid-to-liquid transition in single crystals of high temperature superconductors. Recent results are described, including new contact configurations, allowing both longitudinal and transverse vortex correlations to be studied in one crystal during a single temperature sweep at constant field.     

Nb3Te4单晶输运性质及磁化率测量

测定了Ｎｂ３Ｔｅ４单晶在不同磁场及电场作用下Ｒ（Ｔ）／Ｒ（３００Ｋ）－Ｔ曲线，发现磁场对高温Ｐｅｉｅｒｌｓ相变的回滞有“压缩”作用，电场对高温Ｐｅｉｅｒｌｓ相变温度的加滞有“加宽”作用，另外，测量磁化率时还发现，Ｔ〈５０Ｋ时，晶体出现抗磁信号。     

Tb掺杂双钙钛矿氧化物Pr2CoMnO6的磁热效应

采用高温固相反应法制备双钙钛矿氧化物Pr_(2-x)Tb_xCoMnO₆(x=0,0.05,0.1,0.15)系列陶瓷样品,研究了Tb的掺杂量对Pr₂CoMnO₆样品的居里温度、磁熵变以及磁相变的影响。结果表明:系列样品Pr_(2-x)Tb_xCoMnO₆(x=0,0.05,0.1,0.15)的空间点群为单斜晶系P2₁/n,具有良好的单相性;该组样品均有两个磁转变点(T_C1和T_C2);随着Tb掺杂量的增加T_C1和T_C2均降低下降;在测量温区内,随着温度的降低4个样品均先后经历顺磁态、顺磁-铁磁共存态;该组样品在7 T外加磁场中的最大磁熵变值ΔS_M分别为-1.862、-1.779、-1.768和-1.766 J/(kg·K)。掺杂Tb元素使最大磁熵变值变小,但是拓宽了半高宽温区。结合RCP值可以判断,Pr_1.9Tb_0.1CoMnO₆比其他三个样品更具有作为高温区磁制冷材料的潜能;根据对Arrott曲线、重标定曲线以及Loop曲线的分析,该组样品在此阶段经历了一级相变。     

高质量钙钛矿单晶CH3NH3PbI3研究进展

有机-无机钙钛矿材料因为具有光谱吸收范围宽、缺陷密度低、载流子复合率低等非常优良的光电性能吸引了广泛关注, 掀起了钙钛矿材料研究热潮。近年来杂化钙钛矿型太阳能电池发展迅速, 光电转化效率目前已达到22.1%, 展现出极大的应用潜力。与多晶薄膜相比, 单晶具有极低的缺陷密度和极少的界面缺陷。多个课题组成功培养出大尺寸钙钛矿单晶, 发现钙钛矿单晶材料具有比其他薄膜多晶材料更好的光响应特性, 是设计制备光伏器件的理想材料。在各类钙钛矿材料中, CH₃NH₃PbI₃是研究和应用最广泛的一类钙钛矿材料。本文主要针对近年来CH₃NH₃PbI₃单晶材料的研究制备进行综述, 介绍了CH₃NH₃PbI₃单晶材料的结构及性能, 重点总结了CH₃NH₃PbI₃单晶材料生长制备方法和应用, 并对其发展趋势进行了展望。     

单晶六硼化镧的制备及主要应用

六硼化镧（LaB6）是一种理想的阴极材料。介绍了LaB6单晶的制备方法及晶体结构特征，讨论了LaB6晶体在摘要热阴极和场发射阵列阴极方面的性能及应用情况。