强耦合磁失措自旋冰系统Dy2Ti2O7单晶生长和基本磁性质测量

利用红外光源浮区法生长出大尺寸、高质量的磁失措自旋冰化合物Dy₂Ti₂O₇单晶体.X射线衍射实验证实晶体具有面心立方结构，空间群为Fd3m，晶胞参数a＝1.0112(2) nm，［111］和［400］方向X射线衍射摇摆曲线半高宽分别仅为0.07°和0.05°.直流磁化率与温度关系测量给出晶体的Van Vleck顺磁因子为2.46×10^-5 m³/mol，有效磁矩μ_eff＝10.24(4)μ_B，Cure-Weiss温度Θ_CW＝1.1 K，揭示Dy₂Ti₂O₇具有弱的铁磁性.对磁性起源的综合分析表明，该自旋冰晶体磁性质主要来源于磁偶极相互作用，且相关最近邻长程偶极相互作用能量标度D_nn＝3.00 K. 关键词： 2Ti₂O₇')" href="#">Dy₂Ti₂O₇ 浮区法晶体生长 关联电子系统 自旋冰     

Mn替代对Dy2AlFe16-xMnx化合物的结构和磁性的影响

通过X射线衍射及磁测量手段研究了Dy2AlFe16-xMnx化合物的结构和磁性.研究结果表明Dy2AlFe16-xMnx化合物具有六角相的Th2Ni17型结构.对x=1,2的样品采用X射线热膨胀测定法在104-647K的温度范围内测量了其热膨胀性质,发现这些化合物在低温下存在热膨胀反常现象,在居里点附近出现负膨胀性质.对自发磁致伸缩的研究结果表明Dy2AlFe16-xMnx化合物中存在着较强的各向异性的自发磁致伸缩,随着Mn含量的增加,其低温下的自发体磁致伸缩减弱.磁测量结果表明Mn的替代导致Dy2AlFe16-xMnx化合物的居里温度及自发磁化强度急剧下降.     

Dy2 AlFe13 Mn3 化合物的本征磁致伸缩

通过X-射线衍射及磁测量手段研究了Dy2AlFe13Mn3化合物的结构及磁性质。研究结果表明Dy2AlFe13Mn3化合物具有六角相的Th2Ni17型结构。通过X-射线热膨胀测定法发现Dy2AlFe13Mn3化合物在245到344K的温度范围内存在负热膨胀现象，其平均热膨胀系数为α＝-1.1×10-4K-1K-1。在105到360K的温度范围内，通过比较磁性状态下的晶胞参数和由高温顺磁状态外延得到的低温顺磁状态下的晶胞参数间的差别计算了Dy2AlFe13Mn3化合物的本征磁致伸缩。结果表明Dy2AlFe13Mn3化合物的本征体磁致伸缩ωS在105到245K的温度范围内随着温度的升高而增大，由105K时的7.0×10-3 增加到245K时的9.1×10-3。随着温度的进一步升高，ωS反而减小。沿c轴方向的本征线磁致伸缩λc随着温度的升高而减小。基面内的本征线磁致伸缩λa在105到270K的温度范围内随着温度的升高而增大，从105K时的0.8×10-3增大到270K时的3.4×10-3，然后随着温度的进一步升高而减小。     

在MgO衬底上制作Tl2Ba2CaCu2O8超导薄膜

在MgO衬底上,利用共蒸发方法制备DyBa2Cu3O7作为缓冲层,再利用磁控溅射和后处理方法,制备了Tl2Ba2CaCu2O8超导薄膜.X射线衍射θ～2θ及φ扫描结果表明Tl-2212薄膜、Dy-123薄膜与衬底MgO呈外延生长关系.制备的Tl-2212薄膜Tc＝105.5K,液氮温度下临界电流密度Jc＝2.5×106A/cm2.     

SrAl_2B_2O_7:Dy~(3+)材料的制备及其发光性能

采用高温固相法制备了SrAl2B2O7:Dy3+发光材料.在350nm紫外光激发下,测得SrAl2B2O7:Dy3+材料的发射光谱为一个多峰宽谱,主峰分别为480,573和678nm;分别和Dy3+的4F9/2→6H15/2,4F9/2→6H13/2,4F9/2→6H11/2的跃迁发射相对应;监测573nm的发射峰,得到材料的激发光谱为一个多峰宽谱,主峰分别为295,325,350,365,400nm.研究了Dy3+掺杂浓度对SrAl2B2O7:Dy3+材料发射光谱的影响,随着Dy3+掺杂浓度的增大,SrAl2B2O7:Dy3+材料的Iy/Ib逐渐增大,根据Judd-Ofelt理论解释了其原因.随着Dy3+掺杂浓度的增大,Dy3+的4F9/2→6H13/2跃迁产生的573nm发射峰强度先增大,在4%时达到最大值,之后减小,其自身的浓度猝灭机理为电偶极-电偶极相互作用.不同的电荷补偿剂Li+,Na+,K+的引入均使发光强度得到提高,尤其以Li+最佳,发光强度提高了大约33%.     

K2O·CaO·4B2O3·12H2O∶Nd3+的合成及发光性能

以CaCl2、K2B4O7和Nd2O3为原料,采用易于工业化、无污染的水溶液法反应合成碱-碱土金属硼酸盐K2O·CaO·4B2O3·12H2O∶Nd3+晶体,利用X射线衍射、红外光谱、扫描电镜、荧光分光度计等现代分析测试手段,对所合成晶体进行了分析和表征.结果表明,所制备的K2O·CaO·4B2O3·12H2O∶Nd3...     

Y2O3-Eu2O3-SnO2三元系固相线下相关系及其发光性质研究

采用固态反应法及改良固态反应法合成了一系列Y2O3-Eu2O3-SnO2体系中的试样,利用X射线粉末衍射法测定了Y2O3-Eu2O3-SnO2三元系固相线下的相关系.结果表明,Y2O3-Eu2O3二元系和Eu2Sn2O7-Y2Sn2O7赝二元系形成连续固溶体.对于(Y1-xEux)2Sn2O7,最强的发光峰位置在590 nm附近,源于Eu3+的5 D0-7 F1的磁偶极跃迁.对于(Y1-xEux)2O3,最强峰的位置在611 nm附近,是由Eu3+的5 D0-7 F2的电偶极跃迁引起的.激发光谱表明,与(Y1-xEux)2O3相比,(Y1-xEux)2Sn2O7的电荷迁移带向低能方向移动.Eu3+在化合物中所处的晶体学位置决定了其光谱特征.     

K2O·CaO·4B2O3·12H2O∶Nd3+的合成及发光性能

以CaCl2、K2B4O7和Nd2O3为原料,采用易于工业化、无污染的水溶液法反应合成碱-碱土金属硼酸盐K2O·CaO·4B2O3·12H2O∶Nd3+晶体,利用X射线衍射、红外光谱、扫描电镜、荧光分光度计等现代分析测试手段,对所合成晶体进行了分析和表征.结果表明,所制备的K2O·CaO·4B2O3·12H2O∶Nd3+晶型发育良好、形貌规整.基质本身具有上转换发光特性,K2O·CaO·4B2O3·12H2O∶Nd3+的发光强度较基质弱.当激发源为828 nm时,材料呈橙红色光.     

(Nd1-xErx)3Fe273Ti17化合物的结构与磁性

通过x射线衍射分析和磁性测量对(Nd1-xErx)3Fe273Ti17化合物的结构与磁性进行了研究.单相(Nd1-xErx)3Fe273Ti17化合物的成相范围为x=00—05之间，所有化合物均属于单斜晶系、Nd3(Fe,Ti)29型结构和A2/m空间群.着Er含量的增加，(Nd1-xErx)3Fe273Ti17化合物的晶胞体积、居里温度TC和5K下的饱和磁化强度Ms均单调减小，而5K下的饱和磁化强度Ms和Er含量的关系与稀释模型所描述的结果相一致.(Nd1-xErx)3Fe273Ti1 关键词： (Nd1-xErx)3Fe273Ti17化合物 磁晶各向异性 自旋重取向 磁相图     

Gd3Co29-xCrx新相化合物的结构与磁性

制备出具有室温单轴磁晶各向异性的非间隙型Co基Gd3Co29-xCrx化合物(x=65和70)，x射线衍射和磁性测量表明所有单相化合物均属于单斜晶系，Nd3(Fe,Ti)29型结构和A2/m空间群.Gd3Co29-xCrx化合物的居里温度在x=65时为412 K，x=70时为359 K. Gd3Co29-xCrx化合物在x=65 时磁化强度随温度的变化曲线表明，在居里温度以下的某一温度处有一补偿点，在补偿点处求得晶格分子场系数nRT=33 T f.u./μB. 关键词： Gd3Co29-xCrx化合物 x射线衍射 磁晶各向异性     

Controlled vapor growth of 2D magnetic Cr_2Se_3 and its magnetic proximity effect in heterostructures

Two-dimensional(2 D) magnetic materials have aroused tremendous interest due to the 2 D confinement of magnetism and potential applications in spintronic and valleytronic devices. However, most of the currently 2 D magnetic materials are achieved by the exfoliation from their bulks, of which the thickness and domain size are difficult to control, limiting the practical device applications. Here, we demonstrate the realization of thickness-tunable rhombohedral Cr_2Se_3 nanosheets on different substrates via the chemical vapor deposition route. The magnetic transition temperature at about 75 K is observed. Furthermore, van der Waals heterostructures consisting of Cr_2Se_3 nanosheets and monolayer WS_2 are constructed.We observe the magnetic proximity effect in the heterostructures, which manifests the manipulation of the valley polarization in monolayer WS_2. Our work contributes to the vapor growth and applications of 2 D magnetic materials.     

Structures and magnetic behaviours of TiO2-Mn-TiO2 multilayers

The TiO2-Mn-TiO2 multilayers are successfully grown on glass and silicon substrates by alternately using radio frequency reactive magnetron sputtering and direct current magnetron sputtering. The structures and the magnetic behaviours of these films are characterised with x-ray diffraction, transmission electron microscope (TEM), vibrating sample magnetometer, and superconducting quantum interference device (SQUID). It is shown that the multi-film consists of a mixture of anatase and rutile TiO2 with an embedded Mn nano-film. It is found that there are two turning points from ferromagnetic phase to antiferromagnetic phase. One is at 42 K attributed to interface coupling between ferromagnetic Mn3O4 and antiferromagnetic Mn2O3, and the other is at 97 K owing to the interface coupling between ferromagnetic Mn and antiferromagnetic MnO. The samples are shown to have ferromagnetic behaviours at room temperature from hysteresis in the M-H loops, and their ferromagnetism is found to vary with the thickness of Mn nano-film. Moreover, the Mn nano-film has a critical thickness of about 18.5 nm, which makes the coercivity of the multi-film reach a maximum of about 3.965×10 2 T.     

Strain engineering of electronic and magnetic properties of Ga_2S_2 nanoribbons

Using first-principles calculations, we study the tailoring of the electronic and magnetic properties of gallium sulfide nanoribbons(Ga_2S_2NRs) by mechanical strain. Hydrogen-passivated armchair-and zigzag-edged NRs(ANRs and ZNRs)with different widths are investigated. Significant effects in band gap and magnetic properties are found and analyzed. First,the band gaps and their nature of ANRs can be largely tailored by a strain. The band gaps can be markedly reduced, and show an indirect-direct(I-D) transition under a tensile strain. While under an increasing compressive strain, they undergo a series transitions of I-D-I-D. Five strain zones with distinct band structures and their boundaries are identified. In addition,the carrier effective masses of ANRs are also tunable by the strain, showing jumps at the boundaries. Second, the magnetic moments of(ferromagnetic) ZNRs show jumps under an increasing compressive strain due to spin density redistribution,but are unresponsive to tensile strains. The rich tunable properties by stain suggest potential applications of Ga_2S_2 NRs in nanoelectronics and optoelectronics.     

Pressure effect on magnetic phase transition and spin-glass-like behavior of GdCo_2B_2

We systematically investigate the effect of pressure on the magnetic properties of GdCo_2B_2 on the basis of alternating current(AC) susceptibility,AC heat capacity and electrical resistivity measurements under pressures up to 2.2 GPa.A detailed magnetic phase diagram under pressure is determined.GdCo_2B_2 exhibits three anomalies that apparently reflect magnetic phase transitions,respectively,at temperatures T_C= 20.5 K,T_1= 18.0 K and T_N= 11.5 K under ambient pressure.Under pressures up to 2.2 GPa,these anomalies are observed to slightly increase at T_Cand T_1,and they coincide with each other above 1.6 GPa.Conversely,they decrease at T_N and disappear under pressures higher than 1.4 GPa.The results indicate that the low-temperature magnetic phases can be easily suppressed by pressure.Moreover,the spin-glass-like behavior of GdCo_2B_2 is examined in terms of magnetization,aging effect and frequency dependence of AC susceptibility.A separation between the zero-field-cooled(ZFC) and field-cooled(FC) magnetization curves becomes evident at a low magnetic field of 0.001 T.A long-time relaxation behavior is observed at 4 K.The freezing temperature Tfincreases with frequency increasing.     

Incommensurate-commensurate magnetic phase transition in double tungstate Li2Co(WO4)2

Magnetic susceptibility, specific heat, and neutron powder diffraction measurements have been performed on polycrystalline Li$_{2}$Co(WO$_{4}$)$_{2}$ samples. Under zero magnetic field, two successive magnetic transitions at $T_{\rm N1}\sim 9.4$ K and $T_{\rm N2}\sim 7.4$ K are observed. The magnetic ordering temperatures gradually decrease as the magnetic field increases. Neutron diffraction reveals that Li$_{2}$Co(WO$_{4}$)$_{2}$ enters an incommensurate magnetic state with a temperature dependent $\bm k$ between $T_{\rm N1}$ and $T_{\rm N2}$. The magnetic propagation vector locks-in to a commensurate value $\bm k = (1/2, 1/4, 1/4)$ below $T_{\rm N2}$. The antiferromagnetic structure is refined at 1.7 K with Co$^{2+}$ magnetic moment 2.8(1) $\mu_{\rm B}$, consistent with our first-principles calculations.     

Dynamic magnetic properties in the kinetic mixed spin-2 and spin-5/2 Ising model under a time-dependent magnetic field

We extend the recent paper [W. Jiang, V-C. Lo, B-D. Bai, J. Yang, Physica A 389 (2010) 2227-2233] to present a study, within a mean-field approach, the dynamic magnetic properties of the mixed spin-2 and spin-5/2 Ising ferrimagnetic system, which corresponds the molecular-based magnetic materials AFe^IIFe^III(C₂O₄)₃ [ A=N(n-C_nH_2n+1)₄, n=3-5], by using the Glauber-type stochastic dynamics. This mixed Ising ferrimagnetic system is used on a layered honeycomb lattice in which Fe^II (S=5/2) and Fe^III (σ=2) occupy sites. First, we investigate the time variations of average order parameters to find the phases in the system and then the thermal behavior of the dynamic order parameters to obtain the dynamic phase transition (DPT) points as well as to characterize the nature (first-or second-order) phase transitions. We also present the dynamic phase diagrams and study the dynamic magnetic hysteresis loop behaviors of the kinetic mixed spin-2 and spin-5/2 Ising ferrimagnetic system. The results are compared with some experimental and theoretical works and a good overall agreement is found.     

CdS:Mn/SiO2复合纳米颗粒的反常的磁学特性

采用反胶束法,合成了硅土包裹的Mn2+掺杂的CdS纳米颗粒。利用高分辨透射电镜(HRTEM)和电子自旋共振谱 (EPR) 对这些纳米颗粒的结构进行了表征。利用超导量子干涉磁力计（SQUID）测量了这些纳米颗粒在低温下的磁学特性。研究结果表明：扩散在硅土基质中的CdS:Mn纳米颗粒的磁滞回线相对于磁场轴有明显的偏移,而有致密包裹层SiO2的CdS:Mn纳米颗粒却使磁滞回线的偏移消失,对于磁性纳米颗粒在磁化过程中出现的这一奇特的现象进行了合理的解释。     

CdS:Mn/SiO2复合纳米颗粒的反常的磁学特性

采用反胶束法,合成了硅土包裹的Mn2+掺杂的CdS纳米颗粒。利用高分辨透射电镜(HRTEM)和电子自旋共振谱 (EPR) 对这些纳米颗粒的结构进行了表征。利用超导量子干涉磁力计（SQUID）测量了这些纳米颗粒在低温下的磁学特性。研究结果表明：扩散在硅土基质中的CdS:Mn纳米颗粒的磁滞回线相对于磁场轴有明显的偏移,而有致密包裹层SiO2的CdS:Mn纳米颗粒却使磁滞回线的偏移消失,对于磁性纳米颗粒在磁化过程中出现的这一奇特的现象进行了合理的解释。     

Possible coexistence of superconductivity and magnetic order in NdPt2B2C

Coexistence of superconductivity and magnetic order has been one of the exciting aspects of the quaternary borocarbide superconductors, So far, RNi₂B₂C (R=Tm, Er, Ho and Dy) are the only known magnetic superconductors in this family. Here, we present our resistivity, magnetization and heat capacity studies on NdPt₂B₂C (nominal composition, NdPt_1.5Au_0.6B₂C and NdPt_2.1B_2.4C_1.2). We find superconductivity in both samples with T _c,onset ∼ 3 K. Bulk magnetic order is found to occur below 1.7 K. We suggest that NdPt₂B₂C is a possible magnetic superconductor.     

Sc掺杂SnO2稀磁半导体的第一性原理研究

采用第一性原理方法,对Sc掺杂SnO2以及含有O空位的Sc掺杂SnO2的电子结构和磁学性质进行了计算。结果表明SnO2晶格中存在两种本征磁性来源,分别为Sc掺杂诱导的未配对O-2p态电子的自旋极化和O空位诱导的未配对Sn-5p态电子的自旋极化。由于两种未配对的弱束缚电子分别由电离施主和受主诱导产生,因此二者之间存在电荷补偿效应,在特定配比下能够使SnO2晶格出现磁性猝灭。