Synthesis and Magnetic Properties of L0.5Sr0.5Mn0.5M0.5O3 (L = Y, Pr; M = Cu, Ru)

A new Mn-containing material with nominal composition L_0.5Sr_0.5Mn_0.5M_0.5O₃ (L = Y or Pr; M = Cu or Ru), as well as Y_0.5Sr_0.5MnO₃ for comparison, were synthesized. The results of the XRD and EDX analyses show that the obtained samples are single-phased and isostructural, with L_1–xA_xMnO₃. The L_0.5Sr_0.5Mn_0.5Cu_0.5O₃ material displays a PM behavior down to 8 K where paramagnetic–antiferromagnetic transition begins. The Pr_0.5Sr_0.5Mn_0.5Cu_0.5O₃ sample has a broad transition at 210 K and a magnetoresistance of 34% at 128 K. The Pr_0.5Sr_0.5Mn_0.5Ru_0.5O₃ material has a paramagnetic–ferromagnetic transition beginning at 330 K and a ferromagnetic–antiferromagnetic one at about 160 K. The obtained value of T _c is the highest for the Pr-containing manganites. The roles of Pr/Sr ratio, anisotropy, and intergranular effects in the samples are discussed.     

Review: Ferromagnetism in Undoped ZrO2 Thin Films

未掺杂氧化锆薄膜的铁磁性研究

宁帅,张政军（清华大学材料学院）

创新点说明：1,通过不同的物理气相沉积方法,实现了对未掺杂氧化锆薄膜的物相调控;2,发现了未掺杂氧化锆薄膜室温铁磁性对物相结构的依赖性;3,通过缺陷分析表征,发现四方相氧化锆的室温铁磁性主要由氧空位缺陷调控。

目的：未掺杂氧化锆薄膜的制备、物相和缺陷调控以及室温铁磁性研究。

方法：脉冲电子束沉积、直流反应磁控溅射、电子束蒸镀。

结果：1,通过不同的物理气相沉积方法,实现了未掺杂氧化锆薄膜的物相调控;2,发现了未掺杂氧化锆薄膜室温铁磁性的物相依赖性;3,通过缺陷分析表征,发现四方相氧化锆的室温铁磁性主要由氧空位缺陷调控。

结论： 1,制备了不同物相结构的未掺杂的氧化锆薄膜;2,发现了四方相氧化锆薄膜可以在室温下呈现铁磁性;3,四方相氧化锆薄膜中的室温铁磁性主要由氧空位缺陷引起。

关键词：氧化锆薄膜,物相调控,室温铁磁性,氧空位缺陷

     

铬掺杂CdS纳米棒室温铁磁性及光学性质

具有室温铁磁性能的Cr掺杂CdS纳米棒用简单的溶剂热法被成功地合成。X-射线衍射(XRD)分析表明产物为六方相CdS。 透射电镜(TEM)分析表明,不同铬含量的CdS均为纳米棒,CdS纳米棒长为100-350 nm,平均直径为20-30 nm,几乎与掺入铬的质量无关。 能量色散谱(EDS)测试表明,合成产物由S、Cd和Cr组成。振动样品磁强计(VSM)表明,Cr掺杂CdS纳米棒在室温下具有铁磁性,而没有Cr掺杂CdS纳米棒具有弱铁磁性。Cr掺杂CdS纳米棒(Cr = 4.17 at%,7.31 at%)的饱和磁化强度Ms分别约为3.907和8.798(10-3 emu/g),Hc的矫顽力约为96.21和 137.15 Oe。 CdS纳米棒室温铁磁性能的产生与CdS晶格中Cd原子被Cr的取代有着密切关系。     

Magnetic and magnetotransport properties in the n-type (Ga,Mn)N thin films

We present the magnetic and magnetotransport properties of epitaxial (Ga,Mn)N films with nominal Mn concentration (x=0.1–0.73%) grown by plasma-enhanced molecular beam epitaxy (PEMBE). X-ray diffraction (XRD) reveals that (Ga,Mn)N has the single-phase wurtzite structure without secondary phases. The epitaxial (Ga,Mn)N films were found to exhibit n-type conductivity, ferromagnetic ordering with Curie temperature in the range 550–700 K, and in-plane magnetic anisotropy. The negative magnetoresistance (MR) was observed at temperatures below 50 K and was found to gradually increase with decreasing temperature.     

Ferromagnetism of Ni-Doped ZnO Powders Prepared by Sol-Gel Method above Room Temperature

The magnetic and structural properties of 2% Ni-doped ZnO powers prepared by sol-gel method were studied. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) of the sample do not show existence of any signal of second phase. The X-photoelectron spectroscopy (XPS) of the sample shows the chemical valence of Ni is 2 and the real Ni concentration is 2.19% determined by X-ray fluorescence spectra (XRFS). The magnetic property performed with superconducting quantum interference device (SQUID) shows that the sample exhibits ferromagnetism above room temperature and the Curie temperature (TC) is about 600 K.     

Alloying (In,Mn)As and (Ga,Mn)As: Ferromagnetic (In,Ga,Mn)As Lattice-Matched to InP

An effect of alloying two ferromagnetic semiconductors (In,Mn)As and (Ga,Mn)As on the ferromagnetic properties of resultant (In,Ga,Mn)As alloys is reported. For conditions close to lattice-matching to InP substrates, y = 0.53 in (In _y Ga_1–y )_1–x Mn _x As, ferromagnetism up to Curie temperatures T _C = 100–110 K could be achieved for a Mn composition x = 0.13. Trends in the Curie temperature in (In,Ga,Mn)As are compared with (Ga,Mn)As and (In,Mn)As as a function of Mn content. Hole concentrations determined from magnetotransport, taking into account the anomalous Hall contribution to Hall resistance, gives p/Mn = 0.03 ratio to Mn composition in metallic case for x = 0.13. We mention the possible role of chemical ordering (short range) of Mn impurity atoms on hole concentration and, consequently, for the ferromagnetic properties.     

具有宽过冷液相区的Fe63Co7NbxZr10-xB20非晶态合金的热稳定性和磁性研究

利用单辊急冷法制备出厚约35μm宽5mm的 Fe63Co7NbxZr10-xB20条带,并研究了合金的热稳定性、非晶结构和磁性能.结果表明,含4at%Nb的Fe63Co7Nb4Zr6B20合金过冷液相区Δ Tx最宽,达到79K.合金系的饱和比磁化强度σs随着Nb含量的增加而线性减小.合金系经973K退火900s,由于α\|Fe等相的析出,使得合金的σs和Hc均迅速升高.     

La_(1-x)Na_xMnO_3室温巨磁电阻增强效应

采用固相反应法制备了一系Ｌａ_(１－ｘ)Ｎａ_ｘＭｎＯ_３多晶样品。研究了样品的微结构、磁电阻、磁化强度以及居里温度等性质。发现随着Ａ位平均离子半径＜ｒ_Ａ＞的减小,样品的居里温度下降,磁电阻增大。另外,实验还发现了磁电阻与磁化强度之间有着密切的联系。     

Fine Strontium Ferrite Powders from an Ethanol-Based Microemulsion

A fine strontium ferrite powder with high coercivity was successfully prepared by forming hydroxide precursor particles in the continuous ethanol-based phase of a microemulsion consisting of iso-octane, NP9, and an ethanol solution containing Sr²⁺ and Fe³⁺ cations at a molar ratio of 1:12. The microemulsion-derived hydroxide precursor was calcined at various temperatures, ranging from 600° to 1100°C, to develop the hexagonal strontium ferrite phase. X-ray diffractometry and infrared characterizations revealed that the formation mechanisms of strontium ferrite in the microemulsion-derived precursor differed from those of the precursor derived by conventional coprecipitation. The microemulsion resulted in a strontium ferrite of finer particle size and better magnetic properties than those of the conventionally coprecipitated strontium ferrite. The microemulsion-derived strontium ferrite exhibited an intrinsic coercivity of 6195 Oe and a saturation magnetization of 58.28 emu/g when calcined at 900^oC. The saturation magnetization increased further, to 69.75 emu/g, when the microemulsion-derived precursor was calcined at 1100^oC.