Structural and Magnetic Properties of Sm Implanted GaN

The structural and magnetic properties of Sm ion-implanted GaN with different Sm concentrations are investigated. XRD results do not show any peaks associated with second phase formation. Magnetic investigations performed by superconducting quantum interference device reveal ferromagnetic behavior with an ordering tem- perature above room temperature in all the implanted samples, while the effective magnetic moment per Sin obtained from saturation magnetization gives a much higher value than the atomic moment of Sm. These results could be explained by the phenomenological model proposed by Dhar et al. [Phys. Rev. Lett. 94（2005）037205, Phys. Rev. B 72（2005）245203] in terms of a long-range spin polarization of the GaN matrix by the Sm atoms.     

Pr_(0.75)Na_(0.25)Mn_(1-x)Fe_xO_3的制备及磁学和输运性质研究

采用溶胶凝胶法通过较低温度、较短的烧结时间制备了单相的多晶钙钛矿Pr0.75Na0.25Mn1-xFexO3(0≤x≤0.3),避免了Na元素的挥发及锰氧化物的析出,使Pr1-xNaxMnO3中Na的最大掺入量由文献报道的0.19提高到0.25,样品单相性得到大幅度提高.系列样品的磁化强度、电阻率随温度的变化关系表明2%的Fe掺杂便能大大减弱低温电荷有序;在x≤0.05时系列样品磁化强度随Fe含量的增加而增加,电阻率随Fe含量的增加而下降,然后二者随Fe含量进一步增加均朝相反的趋势变化.用几何效应(Fe3+的几何尺寸大小)和电子结构的影响两个方面的竞争解释这种现象.     

考虑非常数自旋扭矩时LLS方程的微扰解

不将自旋扭矩因子近似为一个常数,利用Melnikov微扰方法推导了LLS方程解的表达式,通过VC与MATLAB混和编程进行计算,计算结果显示,与将自旋扭矩因子视为常数的情况相比较,自旋扭矩为磁化强度函数时的磁化强度运动轨道在离开未扰轨道初期仅在未扰轨道附近做微小振动,在翻转时刻附近有较大振荡,并且所预言的磁化强度翻转时刻相对提前. 关键词： 自旋扭矩 磁化强度 LLS方程 微扰     

氧化-共沉淀法制备Mn-Zn铁氧体的机理及影响因素

以FeSO4.7H2O、MnSO4.H2O、ZnSO4.7H2O、HCl为原料,NaOH溶液为沉淀剂、H2O2为氧化剂,采用氧化-共沉淀法在液相中制备Mn-Zn铁氧体,通过傅里叶变换红外光谱仪(IR),X射线衍射仪(XRD)和振动样品磁强计(VSM)对样品进行表征,讨论了Mn-Zn铁氧体在液相中的形成机理和氧化共沉淀法制备Mn-Zn铁氧体的影响因素。结果表明:采用氧化-共沉淀法能在液相中直接制备出Mn-Zn铁氧体,溶液的浓度和pH值是形成单相Mn-Zn铁氧体的两个关键因素;溶液的浓度和pH值低时,制备出的样品中含有非晶相FeOOH且饱和磁化强度低。     

Magnetic Properties of Transverse Ising Model under a Time Oscillating Longitudinal Field

A transverse Ising spin system, in the presence of time-dependentlongitudinal field, is studied by the effective-field theory (EFT). Theeffective-field equations of motion of the average magnetization are givenfor the simple cubic lattice (Z = 6) and the honeycomb lattice (Z = 3).The Liapunov exponent λ is calculated for discussing the stability of the magnetization and it is used to determine the phase boundary. Thedynamic phase transition diagrams in h₀/ ZJ -Γ/ZJ plane and in h₀/ZJ-T/ZJ plane have been drawn, and there is no dynamical tricritical point on the dynamic phase transition boundary. The effect of the thermal fluctuations upon the dynamic phase boundary has been discussed.     

前驱物合成条件对锰锌铁氧体结构和性能的影响

采用共沉淀-热处理工艺合成了尖晶石型锰锌铁氧体粉末,利用正交试验优化了制备工艺。利用X射线衍射仪(XRD)扫描电子显微镜(SEM)和振动样品磁强计(VSM)对粉体的显微结构和静磁性能进行了研究。结果表明:热处理温度为1350℃、保温时间为3.5 h、进料比为1.5时,若前驱物的pH值为6,制备的样品的主晶相为锰锌铁氧体;若前驱物的pH值为7 9,则形成单相尖晶石型锰锌铁氧体,样品的饱和磁化强度先增大后减小,矫顽力逐渐增大。pH值为7时,配方为Fe∶Mn∶Zn=68.4816∶17.1368∶14.381,进料比为1.5,滴加时间为40 min,反应温度为50℃,不加表面活性剂时得到的样品具有较高的饱和磁化强度。     

Finite-Size Scaling Analysis of a Three-Dimensional Blume--Capel Model in the Presence of External Magnetic Field

The Blume-Capel model in the presence of external magnetic field H has been simulated using a cellular automaton algorithm improved from the Creutz cellular automaton in three-dimension lattice. The field critical exponent 5 is estimated using the power law relations and the finite size scaling functions for the magnetization and the susceptibility in the range -0.1≤ h = H/J ≤0. The estimated value of the field critical exponent 5 is in good agreement with the universal value （δ = 5） in three dimensions. The simulations are carried out on a simple cubic lattice under periodic boundary conditions.     

非晶态分子合金低温制备纳米复合氧化物La~1~-~xCa~xMnO~3

钙钛矿型稀土锰氧化物La~1~-~xCa~xMnO~3(RE=La,Pr,Nd,Gd;T=Ca,Sr,Ba,Pb等)因其特殊的巨磁电阻效应,引起人们广泛的关注。用非晶态的分子合金为前驱体,制备了一系列具有纳米尺寸的La-Ca-Mn-O复合氧化物颗粒。研究表明,前驱体的晶化温度对纳米颗粒的形貌和大小均有影响。当晶化温度为450℃-600℃时,从透射电子显微镜观察到的颗粒大小约为25nm-100nm。该纳米材料的磁及磁电阻行为不同于其体相体系,其交流磁化率表现出较较强的尺寸依赖性,而磁电阻具有本征型和自旋隧穿型的巨磁电阻行为。     

一个新型分子铁磁体: 氰根桥联的铜(II)-铁(III)配合物

合成和表征了一个新的分子磁体,氰根桥联的杂化型异金属配合物[Cu(en)]~3[Fe(CN)~6]~2.3H~O(en为乙二胺)。变温磁化率、零场冷却磁化强度(ZFCM)、场冷却磁化强度(FCM)和磁滞回线测量表明铜铁离子间存在着铁磁性相互作用,其铁磁相变温度为T~c=11.0K,矫顽力为20×10^-^4T,剩磁为1.70×10^-^1cm^3.mol^-^1.T。该化合物为杂化型铜(II)-铁(III)普鲁士蓝类中具有铁磁相变温度的首例。