Ni46Mn35Ga19单晶中磁转变和马氏体相变的物理表征及形状记忆效应

NiMnGa是最早发现的铁磁形状记忆合金,是一种新型的形状记忆材料。自发现以来,许多学者对其进行了深入的研究,但对磁转交和马氏体转变共同发生的转变特性却缺乏系统的表征。本文采用多种测量手段,如相变潜热、电阻、交流磁化率和应变测量,对提拉法生长的Ni46Mn35Ga19单晶的磁转变和马氏体相变同时发生的转变行为进行了系统表征;根据合金形状记忆的特点和马氏体变体择优取向的机理,对实验结果进行了分析和讨论。应变测量结果表明,伴随该转变行为,材料展现出应变量达-0．89％的自发双向形状记忆效应和应变量高达-1．90％的磁控形状记忆效应。     

Ni51 Mn25.5 Ga23.5 单晶大的自发相变应变和磁感生应变

通过交流磁化率、电阻、有无磁场下的马氏体相变应变测量,研究了Ni51Mn25.5Ga23.5单晶的马氏体相变和磁感生应变特性。伴随马氏体相变,该单晶展现出一个应变量高达-1.62%的自发双向形状记忆效应。采用磁场下冷却的方法,在材料的马氏体相获得了一个量值高达-1.5%且可逆的磁感生应变,该值近似为零场下冷却测量得到的磁感生应变的2倍。根据单晶生长机制和NiMnGa合金形状记忆特性,对上述结果进行了讨论。     

Ni51Mn25．5Ga23．5单晶大的自发相变应变和磁感生应变

通过交流磁化率、电阻、有无磁场下的马氏体相变应变测量,研究了Ni51Mn25．5Ga23．5单晶的马氏体相变和磁感生应变特性。伴随马氏体相变,该单晶展现出一个应变量高达-1．62％的自发双向形状记忆效应。采用磁场下冷却的方法,在材料的马氏体相获得了一个量值高达-1．5％且可逆的磁感生应变,该值近似为零场下冷却测量得到的磁感生应变的2倍。根据单晶生长机制和NiMnGa合金形状记忆特性,对上述结果进行了讨论。     

反铁磁/非磁结构的磁极化激元色散曲线的研究

在Voigt位形下，依据反铁磁／非磁三明治结构中的磁极化激元的色散关系，研究了此条件下色散曲线，结果表明，磁极化激元发生了分裂．     

Laser-induced ultrafast spin reorientation in the antiferromagnet TmFeO3

All magnetically ordered materials can be divided into two primary classes: ferromagnets and antiferromagnets. Since ancient times, ferromagnetic materials have found vast application areas, from the compass to computer storage and more recently to magnetic random access memory and spintronics. In contrast, antiferromagnetic (AFM) materials, though representing the overwhelming majority of magnetically ordered materials, for a long time were of academic interest only. The fundamental difference between the two types of magnetic materials manifests itself in their reaction to an external magnetic field-in an antiferromagnet, the exchange interaction leads to zero net magnetization. The related absence of a net angular momentum should result in orders of magnitude faster AFM spin dynamics. Here we show that, using a short laser pulse, the spins of the antiferromagnet TmFeO3 can indeed be manipulated on a timescale of a few picoseconds, in contrast to the hundreds of picoseconds in a ferromagnet. Because the ultrafast dynamics of spins in antiferromagnets is a key issue for exchange-biased devices, this finding can expand the now limited set of applications for AFM materials.     

铁磁180°畴层结构中的畴层振动模

本文探讨了具有反平行磁化矢量的铁磁层状结构的磁畴振动谱,给出了普遍的色散方程.当外加磁场为零,整个分布成180°畴层状态时,给出了一般的色散曲钱.理论预言可能同时存在一种具有二维铁磁性和一维反铁磁性的新型磁有序材料.     

磁弹磨粒双磁盘磁力钝化仿真与实验研究

磁弹磨粒具有磁性、低弹性模量以及优良的研磨性能，能够提高加工效率和加工质量。首先，基于磁场基本理论和磁弹磨粒特性，分析了磁弹磨粒双磁盘磁力刀具钝化机制；然后，基于磁场中磁弹磨粒的磁场力对离散元软件EDEM进行二次开发，建立了磁弹磨粒双磁盘磁力刀具钝化过程仿真模型，研究了磨粒粒度、磁化率和磁盘间距对刃口碰撞次数和磨粒旋转速度的影响规律；最后，采用Matlab软件对刀具刃口轮廓进行重建，提出了基于钝化面积的改进形状因子表征方法，通过正交实验研究了磨粒粒度、磁化率和磁盘间距对刃口钝化量的影响规律，并验证了所提改进形状因子表征方法的可行性。结果表明：随着磁弹磨粒粒度的增大、磁化率的增加和磁盘间距的减小，刃口碰撞次数和磨粒旋转速度增大；钝化参数对刃口钝化量的影响程度大小依次为磨粒粒度、磁盘间距、磁化率，最优钝化参数组合为磨粒粒度40目、磁化率0.1、磁盘间距15 mm；仿真与实验钝化面积的最大相对误差为16.33%，最小相对误差为0.42%，仿真能够较好地预测刃口钝化形貌，且改进的刃口形状因子能够较好地表征刀具刃口钝化形貌。     

稀土氟化物PrF3的磁光效应与磁性

本文计算了稀土氟化物 PrF_3的 Faraday 旋转的 Verdet 常数及其磁化率,并研究了它们的温度特性.结果表明,该化合物在可见光范围内的 Faraday 效应主要是由 Pr~(3 )离子的4f 电子在4f~2和4f5d 两组态之间的允许电偶极跃迁引起的,在考虑了晶场和外磁场的共同影响,并把 Pr~(3 )离子的~3H_4态作为基态的情况下,不引入任何可调参数,计算结果与实验符合较好。     

Ni46Mn35Ga19单晶中磁转变和马氏体相变的物理表征及形状记忆效应

NiMnGa是最早发现的铁磁形状记忆合金,是一种新型的形状记忆材料。自发现以来,许多学者对其进行了深入的研究,但对磁转交和马氏体转变共同发生的转变特性却缺乏系统的表征。本文采用多种测量手段,如相变潜热、电阻、交流磁化率和应变测量,对提拉法生长的Ni46Mn35Ga19单晶的磁转变和马氏体相变同时发生的转变行为进行了系统表征;根据合金形状记忆的特点和马氏体变体择优取向的机理,对实验结果进行了分析和讨论。应变测量结果表明,伴随该转变行为,材料展现出应变量达-0．89％的自发双向形状记忆效应和应变量高达-1．90％的磁控形状记忆效应。     

磁各向异性对YIG单晶磁性薄膜△H的贡献

在考虑任意磁化方向单轴和立方磁各向异性等效场的基础上，根据磁短进动方程，导出了张量磁化率X”的表达式，讨论了单晶YIG磁性薄膜中磁各向异性对铁磁共振线宽的贡献，用“各向异性线宽因子”的概念定量描述了这种贡献．理论计算与实验结果符合得很好．     

Magnetic-field-induced shape recovery by reverse phase transformation

Large magnetic-field-induced strains have been observed in Heusler alloys with a body-centred cubic ordered structure and have been explained by the rearrangement of martensite structural variants due to an external magnetic field. These materials have attracted considerable attention as potential magnetic actuator materials. Here we report the magnetic-field-induced shape recovery of a compressively deformed NiCoMnIn alloy. Stresses of over 100 MPa are generated in the material on the application of a magnetic field of 70 kOe; such stress levels are approximately 50 times larger than that generated in a previous ferromagnetic shape-memory alloy. We observed 3 per cent deformation and almost full recovery of the original shape of the alloy. We attribute this deformation behaviour to a reverse transformation from the antiferromagnetic (or paramagnetic) martensitic to the ferromagnetic parent phase at 298 K in the Ni45Co5Mn36.7In13.3 single crystal.     

空穴型掺杂双层三角晶格反铁磁体积分自旋动力学研究

从t-J模型出发,在feimion-spin理论框架下研究了空穴型掺杂双层三角晶格反铁磁体积分自旋动力学.结果表明,与四方晶格材料不同,空穴型掺杂双层三角晶格反铁磁体积分自旋动力学不具有普适行为.结果还表明对于三角晶格反铁磁体,2个CuO2平面之间的耦合对自旋动力学的影响不是很大,双层三角晶格反铁磁体的自旋动力学与单层三角晶格大体相同.     

舰船上层建筑模型的等效磁化率研究

研究了感应磁场计算中的等效磁化率的概念．１个有规则的内部有纵隔和横隔的多面钢质上层建筑模型可以用１个同一几何形状的实心钢体来替代，只是其磁化率需换成等效磁化率．计算结果表明，这种等效替代所得的计算误差较小．这个概念能应用于实际舰船感应磁场的计算机辅助分析的建模，以减少计算单元与缩短计算时间     

空穴型掺杂三角晶格反铁磁体反常的c-轴电荷动力学

从t-J模型出发,在feimion-spin理论框架下研究了空穴型掺杂三角晶格反铁磁体的c-轴电荷动力学.结果表明,与四方晶格材料类似,空穴型掺杂三角晶格反铁磁体正常态的电荷动力学同样具有很强的各向异性,但是由于三角晶格固有的几何阻挫效应,使得二者的结果又稍有差异.     

磁场影响水溶液冰晶的试验及装置

为寻找生物组织低温无损保存的新方法,研究了磁场对KMnO4溶液冰晶形成的影响.建立了不同形式的磁场发生装置,包括旋转磁场、方波叠加正弦波磁场、50kHz磁场.为保证样品降温过程慢速均匀,运用虚拟仪器技术建立了温度测控系统.使用低温显微系统对磁场影响下样品冰晶的形态进行了记录.结果表明,低频旋转磁场对生物溶液冰晶的形成产生了影响,尤其50kHz交变磁场对溶液中冰晶的生长具有较为显著的抑制作用,说明在易于产生的低冷冻速率下,交变磁场对生物组织的低温无损保存研究具有重要意义,适合实际应用.     

基于时域伪谱法的二维光子带隙结构的能带研究

根据Bloth定理推导了伪周期电磁场的麦克斯韦方程,采用时域伪谱(PSTD)法分析二维光子带隙结构(PBG)的能带,对空间的微分进行付里叶变换离散而不作差分近似离散,使空域变换成伪谱域.计算结果与平面波展开法的结论相一致.分析了不同截面形状在不同的典型点阵结构中的物理特性.     

Ordering and manipulation of the magnetic moments in large-scale superconducting pi-loop arrays

The phase of the macroscopic electron-pair wavefunction in a superconductor can vary only by multiples of 2pi when going around a closed contour. This results in quantization of magnetic flux, one of the most striking demonstrations of quantum phase coherence in superconductors. By using superconductors with unconventional pairing symmetry, or by incorporating pi-Josephson junctions, a phase shift of pi can be introduced in such loops. Under appropriate conditions, this phase shift results in doubly degenerate time-reversed ground states, which are characterized by the spontaneous generation of half quanta of magnetic flux, with magnitude 1/2 Phi(0)(Phi(0) = h/2e = 2.07 x 10(-15) Wb) (ref. 7). Until now, it has only been possible to generate individual half flux quanta. Here we report the realization of large-scale coupled pi-loop arrays based on YBa2Cu3O7-Au-Nb Josephson contacts. Scanning SQUID (superconducting quantum interference device) microscopy has been used to study the ordering of half flux quanta in these structures. The possibility of manipulating the polarities of individual half flux quanta is also demonstrated. These pi-loop arrays are of interest as model systems for studying magnetic phenomena--including frustration effects--in Ising antiferromagnets. Furthermore, studies of coupled pi-loops can be useful for designing quantum computers based on flux-qubits with viable quantum error correction capabilities.     

双偶氮苯掺杂液晶在磁场下的Freedericksz转变

发现掺有机杂质(双偶氮苯)的沿面排列丝状液晶与纯液晶相比,会显著减低在静磁场下发生Freedericksz转变的阈值.而传统的方法则是通过掺入微细的铁粉来降低阈值.这一新现象主要是由于双偶氮苯具有较强的磁化率各向异性,从而导致掺杂液晶的有效磁化率各向异性增大.理论推导的双偶氮苯磁化率各向异性常数要比纯5CB大2个数量级.Freedericksz转变阈值的减低对研究磁场下的非线性光学效应有重大的意义.     

Magnetic susceptibility properties of polluted soils

An investigation of magnetic properties using magnetic susceptibility (χ) and frequency-dependent susceptibility (χfd) was conducted on representative modern pollutants, which include smelted slag dust, automobile exhaust dust and coal ash. Their magnetic susceptibility values are more than 500ξ10⁸ m³/kg, and frequency-dependent susceptibility values less than 3%, indicating that ample ferrimagnetic and scanty superparamagnetic grains occurred in the studied pollutants. Similar to the artificially synthetic polluted soils, the industrially-polluted soils display a negative relationship between magnetic susceptibility and frequency-dependent susceptibility. However, the unpolluted soils, e.g. the Quaternary loess in the Chinese Loess Plateau, show a positive relationship between them. In this note, we propose a convenient and effective approach for identifying the polluted soils.