Magnetoresistance of epitaxial SrRuO3 thin films on a flexible CoFe2O4-buffered mica substrate

We have investigated the magnetoresistance of epitaxial SrRuO₃ (SRO) thin films on a flexible CoFe₂O₄ (CFO)-buffered mica substrate. High-resolution X-ray diffraction and transmission electron microscopy revealed that the SRO film could be epitaxially grown on a mica substrate with a 22-nm-thick CFO buffer layer. The epitaxial relationships were SRO [1–10] || CFO [1–10] || mica [010] and SRO [111] || CFO [111] || mica [001]. Epitaxial SRO thin films exhibited two magnetoresistance (MR) peaks; one peak occurred at a Curie temperature of 160 K (HT-MR) and the other at a low temperature of 40 K (LT-MR). The LT-MR increased more rapidly with an increase of the buffer layer thickness than the HT-MR. The LT-MR was similar for the two orthogonal current directions with respect to the magnetic field. We explained the HT-MR and LT-MR in terms of the suppression of spin fluctuations and the magnetic rotation of crystallographic domains, respectively.     

Quantum chaos and magnetotransport in lateral superlattices: The transition from weak to strong modulation potential

Magnetotransport in lateral superlattices covers a variety of apparently different physics dependent on the amplitude of the modulation potential relative to the Fermi energy ranging from the weakly modulated 2DEG to the antidot lattice. Here we investigate the transition between weak modulation and antidots within the quantum-mechanical theory by studying (i) the single-particle spectrum with respect to quantum signatures of classical chaos and (ii) the change of characteristic features in the magnetoresistance starting from the Kubo formula.     

Anisotropic magnetoresistance in electrodeposited cobalt antidot arrays

Nanosphere lithography is a simple and accessible technique for nanostructuring of materials. Combined with electrodeposition, it allows the production of compact, ordered antidot networks. In contrast to other lithographic techniques, the resulting nanostructure shows periodicity also along the growth axis. Interesting results are expected for the magnetoresistive behavior of such structures as function of thickness, due to the confinement of electronic routes and the strong shape anisotropy. We were able to electrodeposit cobalt antidot structures of homogeneous and controlled thickness directly over silicon substrates. Room temperature anisotropic magnetoresistance (AMR) as function of thickness and nanosphere diameter are presented, with the magnetic field applied in plane, transverse to the applied current. An overlap of two effects is observed. At fields lower than 2 kOe typical hysteretic AMR peaks appear around the coercive field, and tend to disappear for thicker films. At higher fields, a reversible contribution, caused by the forced magnetization that rotates the spin away from the local current direction, lowers the magnetoresistance, before it reaches its saturation value.     

Validity and Limitation of Semi-Classical Approaches to Giant Magnetoresistance in Magnetic Multilayers

The validity and limitation of semi-classical theories on giant magnetoresistance in magnetic multilayers are discussed on the basis of fundamental quantum statistical mechanics.     

Magnetic Relaxation and Its Relation to Magnetoresistance in FeCr2S4 Spinel

Hyperfine Interactions - The temperature dependence of the local electronic and magnetic state of iron in the chalcogenide spinel FeCr2S4 has been studied in detail around the Curie temperature...     

Elastic anomalies in superlattices: An explanation

An explanation for the elastic anomalies that have been previously reported in metallic superlattices is presented. The explanation, valid for superlattices with sharp interfaces, makes use of the charge transfer which occurs when two metals with different work functions are in contact. However, contrary to the case of bulk materials where the transferred charge remains localized at the surface, in thin layers the transferred charge is distributed throughout the layer. This change in charge distribution explains the observed anomalies in the lattice constants and in the elastic properties.     

块体TaP 极大磁阻及量子振荡特性研究

Weyl 半金属因其载流子满足外尔运动方程, 表现出高迁移率、 极大磁阻等新奇量子物性, 从而在无耗散电子器件应用中具有广泛应用前景. 在本文中, 我们系统研究了块体 TaP 样品的磁电输运特性, 获得了高达106 %极大的磁阻特性和显著的SdH 振荡特性. 结合TaP 样品载流子随温度的变化行为, 我们进一步揭示了块体TaP 样品的极大磁阻的物理起源, 在低温下, 其主要来源于样品费米面附近近似补偿的空穴和电子, 而在高温下则主要来源自块体TaP 样品中增强的电子散射作用. 我们的实验结果为理解 Weyl 半金属新奇量子输运特性和器件设计开发提供了实验参考.     

Spin-Dependent Scattering and Giant Magnetoresistance in Magnetic Granular Films

Based on a macroscopic theory in which the spin-dependent interface scattering and the bulk scattering are included, the transport properties in systems of cylindrical magnetic granules are investigated analytically. It is shown that the giant magnetoresistance as well as the resistivities of these systems depend strongly on the size of the granules.     

High Frequency Resonance Features of Giant Magnetoresistance Multilayers

High frequency resonance technique was applied to study of magnetic multilayer Co/Cu films possess the giant magnetoresistance. The results of the ferromagnetic resonance study in 60GHz-80GHz and 1OGHz bands revealed low temperature changes of g-factor after annealing and a very small value of high frequency saturation magnetization. An abrupt change of the specimen impedance was registered in low field low field range for 10GHz. The static magnetic characteristics as hysteresis and magnetoresistance loops were obtained at room temperature for the planar orientation of external magnetic field.     

磁阻传感器测量地磁场的实验数据处理

介绍了磁阻传感器的实验原理,用计算机origin软件对实验数据进行曲线拟合,拟合结果与传统最小二乘法处理数据相吻合。计算了霍尔灵敏度和西安市区地磁场的大小,误差较小。     

Magnetoresistance and magnetic properties of Fe3O4 nanoparticle compacts

In this paper,we report on the magnetic properties of Fe3O4 nanoparticles with different grain sizes under different pressures.In all the samples,the saturated magnetization Ms shows a linear decrease with increasing pressure.The thickness of the magnetic dead layer on the nanoparticle surface nuder different pressures was roughly estimated,which also increases with increasing pressure.The transport measurements of the nanoparticle Fe3O4 compacts show that the low-field magnetoresistance (MR) value is insensitive to the grain size in a wide temperature range;however,the high-field MR value is dependent on grain size,especially at low temperatures.These experimental results can be attributed to the different surface states of the nanoparticles.     

Transport characteristics of Rabi oscillations in the two-band superlattices

We investigated the transport characteristics of Rabi oscillations, by using numerical methods, within a two-band tight-binding model driven by dc－ac electric fields. We found that Rabi oscillations make the long-time average current a sharply change, i.e. the current have resonant peaks appearing. Rabi oscillations are destroyed by dephasing; these peaks are the signatures of Rabi oscillations on the current response. The strong interband coupling will change the conditions of Rabi oscillations and, correspondingly, changes the places where the current resonant peaks appear.     

铁磁多层膜中的力致磁电阻效应

通过研究外应力场下铁磁多层膜系统中的自旋结构,讨论了系统磁电阻对外应力的依赖关系.结果表明,外应力能够诱发磁电阻效应,且其磁电阻紧密依赖于外应力的大小和方向.一般地对铁磁性层间耦合,其磁电阻与外应力之间的关系紧密地依赖于两铁磁层的磁致伸缩系数以及磁晶各向异性之差异.具体地,大小一定的外应力由磁易轴向磁难轴旋转的过程中,磁电阻先缓慢增大后急剧减小,在磁难轴附近变化较敏锐,并出现峰值.外应力方向一定时,磁电阻随应力的增大先敏锐增强后缓慢减小,且应力方向偏离磁易轴越远,变化趋势越显著.特别地,当外应力完全垂直于磁易轴时,应力大小的变化会引起磁电阻翻倍.而外应力场介于8πM/5≤H_λ≤18πM/5时,磁电阻会随应力的旋转单调上升,并在磁难轴附近急剧增强,产生GMR效应;对反铁磁性层间耦合,其GMR效应对应力大小和方向的响应近似地相反于铁磁性层间耦合情形. 关键词： 铁磁/非磁/铁磁三层膜 自旋结构 磁电阻 应力场     

Optical properties of antiferromagnetic/ion-crystal superlattices

Transmission, refraction and absorption properties of an antiferromagnetic/ion-crystal superlattice are investigated. The transmission spectra based on FeF₂/TlBr superlattices reveal that there exist two intriguing guided modes in a wide stop band. Additionally, FeF₂/TlBr superlattices possess either the negative refraction or the quasi left-handedness, or even simultaneously hold them at certain frequencies of two guided modes, which require both negative magnetic permeability of antiferromagnetic layers and negative permittivity of ion-crystal layers. Frequency regimes of the guided modes will be dependent on the magnitude of the external magnetic field. Therefore, handedness and refraction properties of the system can be manipulated by modifying the external magnetic field. Absorption spectra exhibit that absorption corresponding to guided modes is noticeable.     

制备压力对La2/3Sr1/3MnO3的磁电阻效应的影响

 研究了制备压力对纳米块状样品La_2/3Sr_1/3MnO₃的结构、磁学和电学性质的影响。结果表明：样品的晶粒尺寸随制备压力的增加而变小，且不同样品的磁电阻效应不同。低场磁电阻效应在整个实验温区都随制备压力的升高而变弱，这主要是由制备压力使样品晶粒界面连接更紧密所导致；T<200 K时，高场磁电阻效应随制备压力的升高而变强，T>200 K时，高场磁电阻效应随制备压力的升高反而变弱，这主要是由制备压力改变样品的晶粒尺寸所引起。     

Degradation of the Giant Magnetoresistance in Fe/Cr Multilayers Due to Ar-Ion Beam Mixing

The influence of 200 keV Ar-ion irradiation on the interlayer coupling in the Fe/Cr multilayer system exhibiting the giant magnetoresistance effect (GMR) is studied by conversion electron Mössbauer spectroscopy (CEMS), VSM hysteresis loops, magnetoresistivity and electric resistivity measurements and supplemented by the small-angle X-ray diffraction (SAXRD). The increase of Ar ion dose causes an increase of interface roughness, as evidenced by the increase of the Fe step-sites detected by CEMS as a result of which the GMR gradually decreases and vanishes at doses exceeding 1×10¹⁴ Ar/cm². A degradation of GMR with increasing Ar-ion dose is related to the formation of pinholes between Fe layers and the decrease of the antiferromagnetically coupled fraction.