共查询到20条相似文献,搜索用时 218 毫秒
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本文利用高温油相法制备出尺寸、形状均一的 MnO纳米颗粒, X射线衍射图 (XRD) 和透射电子显微镜 (TEM) 照片清晰表明MnO纳米颗粒为单一的面心立方岩盐晶体结构, 尺寸为15nm, 粒径分布很窄. 通过零场冷却 (ZFC) 和带场冷却 (FC)的磁滞回线发现MnO纳米颗粒具有明显的交换偏置效应, 而且磁滞回线同时表现出横向和纵向偏移. 横向偏移说明纳米颗粒中两相复合的存在, 纵向偏移说明了存在自旋玻璃相或者超顺磁相. 进而通过不同频率下随温度变化的交流磁化率的测定, 根据Mydosh的经验数值确认 MnO纳米颗粒表面层为自旋玻璃相, 并得到 MnO纳米颗粒表面自旋玻璃相的转变温度为TSG=32K.
关键词:
纳米颗粒
氧化锰
交换偏置
自旋玻璃 相似文献
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颗粒介质是复杂的多体相互作用体系, 其弹性源自内部的力链结构, 弹性能量处在亚稳态, 具有复杂的弛豫行为. 在常规作用下, 颗粒介质往往呈现明显的弹性弛豫. 应力松弛是应变恒定时应力的衰减现象, 弹性弛豫是应力松弛的主要原因. 在前期工作基础上, 从弹性势能面和双颗粒温度热力学角度分析了弹性弛豫的机理, 量化了弹性应力演化不可逆过程; 基于双颗粒温度热力学计算得到了弹性能、颗粒温度和应力的演化, 其中应力松弛的计算结果与实验结果基本一致, 讨论了颗粒温度初值和输运系数的影响. 指出, 开展力链结构及其动力学研究是揭示宏观弹性弛豫机理的关键. 相似文献
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在自旋电子学研究中,一般以超晶格结构、自旋阀、隧道结来实现,另一种自旋注入典型方法是稀磁半导体材料,如GaMnAs,本文通过颗粒膜实现自旋注入,利用磁控溅射法将Fe颗粒嵌入GaAs阵体上,制备了(GaAs)19Fe81颗粒膜样品,在室温条件下观测到15 μΩ ·cm最大饱和霍尔电阻率,该效应比纯铁的饱和霍尔电阻率大了一个数量级,成功地实现了自旋注入.
关键词:
自旋注入
颗粒膜
巨霍尔效应 相似文献
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单层过渡金属硫化物由于其特有的激子效应以及强自旋-谷耦合性质,在光电子学及谷电子学等方面有着很广阔的应用前景.利用超快时间分辨光谱,本文系统地比较了两类钨基单层硫化物(WS_2和WSe_2)的A-激子动力学和谷自旋弛豫特性.实验结果表明, WS_2单层膜的A-激子弛豫表现为双指数过程,而对于WSe_2,其A-激子衰减表现为三指数过程,且激子的寿命远长于前者. WS_2谷自旋极化弛豫表现为单指数衰减,其寿命约0.35 ps,主要由电子-空穴交换作用所主导.而对于WSe_2,谷自旋弛豫表现出双指数弛豫特性:一个寿命为0.5 ps的快过程和一个寿命为28 ps的慢过程.快过程的弛豫来源于电子-空穴交换作用,而慢过程则由于自旋晶格散射形成暗激子的过程.通过调谐抽运光波长,进一步证实WSe_2较WS_2更容易形成暗激子. 相似文献
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利用偏振时间分辨光谱和时间分辨Kerr旋转谱,研究了GaAs中的InAs单层和亚单层的电子自旋动力学.实验发现,在非共振激发条件下,厚度为1/3单层的InAs亚单层中电子自旋弛豫寿命长达3.4ns,而1个单层厚的InAs层的电子自旋寿命只有0.48ns;而在共振激发条件下,亚单层结构中的电子自旋寿命大大减少,只有70ps,单层InAs中电子自旋寿命没有显著变化.分析表明,低温下InAs单层和亚单层结构中,Bir-Aronov-Pikus(BAP)自旋弛豫机理占主导地位.通过改变材料结构特性和激发条件来改变电子空穴的空间相关性,从而达到控制自旋弛豫的目的.
关键词:
InAs亚单层
自旋弛豫
BAP机理 相似文献
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为了解释Au1-xNix合金(x=0.30—0.42)低温出现电阻率极小值的实验结果,本文提出一个低浓度自旋集团顺磁态合金的模型,得到自旋集团孤立近似下和自旋集团耦合作用下的电阻率公式,并和晶格散射的贡献(由Au80Ni20合金或Au-Cu合金的ρi(T)实验数据代替)联合起来,得到ρ(T)的计算曲线,和实验结果符合得很好。当Tmin,电阻率随温度增高而下降,主要是自旋集团孤立近似下的Kondo效应引起的。自旋集团之间的RKKY耦合作用对电阻率的贡献在低温时大,随着温度增高按1/T规律迅速减小,所以ρ(T)-ρi(T)实验值在相当宽温度范围出现logT关系。随着温度增高,晶格散射对电阻率的贡献将变得重要,当T=Tmin,电阻率出现极小值。
关键词: 相似文献
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We use the spin non-degenerate single impurity Anderson model to investigate the influence of the local spin polarization
to the Kondo effect. By using the Schrieffer-Wolff transformation, we obtain a generalized s-d exchange Hamiltonian, which
describes the interaction between a polarized local spin and conduction electrons. In this case, the singlet is no longer
an eigenstate as shown by variational calculations where the splitting of the local energy Δ = ɛ
d↑ − ɛ
d↓ can be arbitrarily small. The local spin polarization generates the instability of the singlet ground state of the S = 1/2 s-d exchange model.
相似文献
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本文基于s-d相互作用,考虑杂质之间存在RKKY相互作用,提出了一种新的双杂质散射模型。按照这个模型,当一个杂质作自旋翻转散射时,由于杂质之间存在着RKKY关联,它的自旋作为内部自由度会受到限制。由于这种关联,抑制了杂质的自旋翻转散射,结合Kondo的logT项,能形成电阻极大。本文计算了所有可能的“DIS”图(双杂质自能图),在Kondo电阻公式中加入了A/(T02—T2)这样的项。其中A是一个正常数。T0是一个临界温度。当T≤T0时,这个公式不再有意义。这个理论和已有的分子场理论在本质上是不同的.因为它并不依赖于合金中的磁有序.因此当T≥Tc时(Tc是磁有序转变温度),这种机制仍起作用,但分子场理论则不行.这是一种顺磁效应.我们和Cd-Mn(杂质浓度从0.01到0.1at./0)的实验曲线进行了比较,发现符合得很好.最后,我们认为即使在极低浓度下这种机制也是消除Kondo logT发散的主要原因.
关键词: 相似文献
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J. Brenneisen B. Erhardt F. Glatz Th. Kern R. Ott H. Röpke J. Schmälzlin P. Siedle B. H. Wildenthal 《Zeitschrift für Physik A Hadrons and Nuclei》1997,357(4):377-386
The properties of positive-parity states in 32S are compared to predictions of shell model calculations within the complete s-d basis space using the universal s-d shell Hamiltonian. The experimental T = O spectrum is reproduced to excitation energies between 10 and 11.7 MeV, depending on the level spins. The T = 1 spectrum is known and reproduced for the first five 5 MeV in excitation in general and for the first 8 MeV in the case of Iπ = 1+ states. Altogether the excitation energies of 80 positive-parity states are reproduced with a rms deviation of 200 keV. A calculation of radiative widths and branching ratios for γ-decay which uses effective charges and free-nucleon g-factors yields good general agreement with experiment. The need for effective g-factors is felt only in the rare cases of transitions which are governed by the isovector d3/2 → d5/2 M1 matrix element. The spectrum of negative parity, T = 1 states is understood in terms of the weak-coupling model while that of the T = 0 states is comprised of octupole-quadrupole phonon multiplets. Positive-parity states from outside the s-d configuration are first observed between 9.5 and 10.5 MeV excitation energy. 相似文献
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The influence of s-d Coulomb interaction on the superconductive critical temperature Tc of transition element compounds and their dilute alloys was investigated in the frame of Anderson model. Coulomb interaction of electrons with opposite spins on the same atom was considered in a ladder approximation valid when hybridization is sufficiently small while s-d Coulomb interaction has led to the “parquet” summation. It is shown that s-d Coulomb interaction results in the decrease of Tc and hence the electron mechanism of superconductivity seems to be noneffective in systems under consideration. 相似文献
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从实验上揭示了高温超导体YBa2Cu3O7-δ(YBCO)颗粒膜具有准二维结构的输运特征以及超导弱连接行为特征.在此基础上,将超导颗粒膜样品等效为准二维Josephson弱连接阵列系统,讨论了电流引起的二维超导体系中磁通“涡旋-反涡旋”束缚对的拆对激发问题,并给出了自由涡旋分布n(T,I)的分析表达式.将颗粒膜样品的非平衡辐射响应测量结果与电流激发自由涡旋分布n(T,I)相比较,两者具有相似的分布特征.该结果表明,高温超导体颗粒膜
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Ashish Khandelwal V.K. SharmaL.S. Sharath Chandra Parul AroraM.K. Chattopadhyay S.B. Roy 《Journal of magnetism and magnetic materials》2012,324(5):729-734
The magnetic properties of the Co38Ni34Al28 alloy have been studied. The alloy exhibits a first order austenite-martensite phase transition in the temperature region between 155 and 247 K. A strain of 0.07% is produced across this phase transition. The Arrott plots obtained from the isothermal magnetic field dependence of magnetization indicate the presence of spontaneous magnetization both in the austenite and martensite phases, confirming the ferromagnetic character of the alloy up to room temperature. The temperature dependence of the high field magnetization indicates the presence of spin wave excitations, spin wave excitation gap and spin wave-spin wave interactions in the martensite phase. The magnetic anisotropy energy constant for the Co38Ni34Al28 alloy is estimated both with the help of the standard law of approach to saturation of magnetization, and also from the field dependence of magnetization using the field for technical saturation of magnetization. The temperature dependences of these energy terms are compared. The estimated values of the magnetic anisotropy constant seem to be in agreement with the magnitude of the spin wave excitation gap estimated from the temperature dependence of high field magnetization. 相似文献
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We fabricate Fe/Fe oxide granular film by DC sputtering and study the magnetic and transport properties in the insulator region. X-ray photoelectron spectroscopy and transmission electron microscopy confirm the coexistence of iron and Fe2O3. Accompanied with the nonlinear I-V curve and magnetic measurement, we investigate mechanism of sizable magnetoresistance in detail and found the spin in the interface has crucial contribution to the spin tunneling process. 相似文献