双合成反铁磁结构及其对自旋阀巨磁电阻效应的影响

用直流磁控溅射方法制备了双合成反铁磁结构Co₉₀Fe₁₀(5 nm)/Ru(x nm)/Co₉₀Fe₁₀(3 nm)/Ru(y nm)/Co₉₀Fe₁₀(5 nm)(x=0.45,0.45,1.00; y=0.45,1.00,1.00)的系列样品,并对样品的性能及其作为钉扎层对自旋阀巨磁电阻(GMR)效应的影响进行了研究 关键词： 双合成反铁磁 自旋阀 巨磁电阻     

Thermal Stability of Ni-Fe/Co/Au/Co GMR Pseudo-Spin-Valves

Pseudo-spin-valves (PSV) structures, Ni₈₃Fe₁₇-3 nm / Co-2.5 nm / Au-t _Au / Co-2.5 nm, with 2.4t _Au3.2 nm were deposited by UHV magnetron sputtering. The weak ferromagnetic coupling J2×10^-6 J/m² between Ni-Fe/Co and Co layers and GMR effect 3% was found at RT. The GMR amplitude decreases monotonically from 5% at -100°C to 1% at 200°C. However, the slope of R(H) curve, i.e., GMR field sensitivity, is equal to about 1.5%/Oe and remains almost constant in the entire investigated temperature range. Additionally, our PSV display a good thermal stability, with no significant changes of magnetic and transport properties after annealing up to 250°C.     

基于巨磁电阻效应的多功能测量仪

利用巨磁电阻传感器设计了多功能测量仪器,实验表明该测量仪能够精确测量物体的转速和转角,直观地演示行驶车辆对地磁场的扰动.     

Structural effects in the growth of giant magnetoresistance (GMR) spin valves

An investigation has been made of the thin-film structure and interface morphology of giant magnetoresistance (GMR) spin valves of the cobalt/copper/cobalt (Co/Cu/Co) type that were grown on polycrystalline NiO substrates at three different temperatures (150, 300 and 450 K). Sputter-depth-profile analyses indicate that the quality of the layering in the Co/Cu/Co structure was only slightly better for the 150 K sample than for the 300 K sample. For the 450 K sample, however, the Co/Cu/Co structure showed extensive disruption. The similarity in the depth-profiles for the 150 and 300 K samples indicates the sensitivity of the GMR to subtle structural differences.     

The effect of dimerization on the magnetoresistance in organic spin valves

The effect of lattice dimerization on the magnetoresistance (MR) in organic spin valves is investigated based on the Su-Schrieffer-Heeger (SSH) model and the Green's function method. By comparing with the results for a uniform chain, we find that the dimerization of the molecular chain modifies the monotonic dependence of the MR on the bias to an oscillatory one. A sign inversion of the MR is observed when the amplitude of the dimerization is adjusted. The results also show that at a low bias, the MR through a dimerized chain decreases with the increasing bias as well as the increasing chain length, which is consistent with the experimental reports. A further understanding can be achieved by analyzing the electronic states and the spin-dependent transmission spectrum with the parallel and antiparallel magnetization orientations of the two ferromagnetic electrodes.     

自旋阀与多层膜巨磁电阻的特性测量及比较

介绍磁性多层膜中自旋极化输运和巨磁电阻效应,简述自旋阀巨磁电阻与多层膜巨磁电阻在材料组成结构和工作原理方面的区别,利用和改造现有的高校物理实验室中的实验仪器并设计简易的实验电路测量这两种类型的巨磁电阻的磁敏特性,并根据实验测量的结果将这两种传感器在其灵敏度和测量范围上进行比较和研究.     

Magnetic behaviour investigation on symmetric spin valves of Co／Cu／NiFe and NiFe／Cu／Co

In this paper,we have obtained and investigated the magnetic behaviours of the ferromagnetic layer in the symmetric spin valves of Co/Cu/NiFe and NiFe/Cu/Co by measuring with a vibrating sample magnetometer and analysing in terms of the multi-domain Ising models.It has been found that some magnetic layer can have quite different magnetic behaviours in different structures of spin valves,depending on the properties of the under-layer.In our investigation,we have found that the magnetic behaviour of a Co layer depends mainly on the magnetization of the under-layer,whereas this is not the case for the NiFe layer.     

Effect of nano-oxide layers on giant magnetoresistance in pseudo-spin-valves using Co2FeAl electrodes

We studied the pseudo-spin-valves (PSVs) with a structure of Ta/Co₂FeAl/NOL₁/Co₂FeAl/Cu/Co₂FeAl/NOL₂/Ta, where NOL represents the nano-oxide layer. Compared with the normal Co₂FeAl (CFA) PSV with a structure of Ta/Co₂FeAl/Cu/Co₂FeAl/Ta, which shows only a current-in-plane (CIP) giant magnetoresistance (GMR) of 0.03%, the CFA PSV with NOLs shows a large CIP-GMR of 5.84%. The enhanced GMR by the NOLs inserted in the CFA PSV is due to the large specular reflection caused by [(CoO)(Fe₂O₃)(Al₂O₃)] in NOL₁ and [(Fe₂O₃)(Al₂O₃)(Ta₂O₅)] in NOL₂. Another reason is that the roughness of the interface between Ta and CFA is improved by the oxidation procedure.     

Mn-based antiperovskite functional materials： Review of research

Our recent research on the Mn-based antiperovskite functional materials AXMn 3(A:metal or semiconducting elements;X:C or N) is outlined.Antiperovskite carbides(e.g.,AlCMn 3) show large magnetocaloric effect comparable to those of typical magnetic refrigerant materials.Enhanced giant magnetoresistance up to 70% at 50 kOe(1 Oe = 79.5775 A.m-1) over a wide temperature span was obtained in Ga1-xZnxCMn3 and GaCMn3-xNix.In Cu0.3Sn0.5NMn3.2,negative thermal expansion(NTE) was achieved in a wide temperature region covering room temperature(α =-6.8 ppm/K,150 K-400 K).Neutron pair distribution function analysis suggests the Cu/Sn-Mn bond fluctuation is the driving force for the NTE in Cu1-xSnxNMn3.In CuN1-xCx Mn3 and CuNMn3-yCoy,the temperature coefficient of resistivity(TCR) decreases monotonically from positive to negative as Co or C content increases.TCR is extremely low when the composition approaches the critical points.For example,TCR is ～ 1.29 ppm/K between 240K and 320K in CuN0.95C0.05Mn3,which is one twentieth of that in the typical low-TCR materials(～ 25 ppm/K).By studying the critical scaling behavior and X deficiency effect,some clues of localized-electron magnetism have been found against the background of electronic itinerant magnetism.     

Ultralow detection limit of giant magnetoresistance biosensor using Fe_3O_4–graphene composite nanoparticle label

A special Fe_3O_4nanoparticles–graphene(Fe_3O_4–GN) composite as a magnetic label was employed for biodetection using giant magnetoresistance(GMR) sensors with a Wheatstone bridge. The Fe_3O_4–GN composite exhibits a strong ferromagnetic behavior with the saturation magnetization M_S of approximately 48 emu/g, coercivity H_C of 200 Oe, and remanence M_r of 8.3 emu/g, leading to a large magnetic fringing field. However, the Fe_3O_4 nanoparticles do not aggregate together, which can be attributed to the pinning and separating effects of graphene sheet to the magnetic particles. The Fe_3O_4–GN composite is especially suitable for biodetection as a promising magnetic label since it combines two advantages of large fringing field and no aggregation. As a result, the concentration x dependence of voltage difference |?V| between detecting and reference sensors undergoes the relationship of |?V| = 240.5 lgx + 515.2 with an ultralow detection limit of 10 ng/mL(very close to the calculated limit of 7 ng/mL) and a wide detection range of 4 orders.     

一种双臂型低温导热带的性能研究

详细介绍了低温导热带的设计特点。从理论上分析了低温导热带的冷量传输性能和减振特性,得到通过利用高导热率材料可以有效地减小导热温差和降温时间。通过实验验证了低温导热带与制冷机和高温超导滤波器的耦合实验,耦合温差为2.5K。实验结果和理论值基本吻合,分析了造成温差的原因。根据实验结果,提出了新的改进和实施方案。     

Effect of NiAl underlayer and spacer on magnetoresistance of current-perpendicular-to-plane spin valves using Co2Mn(Ga0.5Sn0.5) Heusler alloy

We investigated the effect of a NiAl underlayer and spacer on magnetoresistive (MR) properties in current-perpendicular-to-plane spin valves (CPP-SVs) using Co₂Mn(Ga_0.5Sn_0.5) (CMGS) Heusler alloy ferromagnetic layers. The usage of a NiAl underlayer allowed a high temperature annealing for the L2₁ ordering of the bottom CMGS layer, giving rise to a MR ratio of 10.2% at room temperature. We found that the usage of a NiAl spacer layer also improved the tolerance of the multilayer structure against thermal delamination, which allowed annealing to induce the L2₁ structure in both the bottom and top CMGS layers. However, the short spin diffusion length of NiAl resulted in a lower MR ratio compared to that obtained using a Ag spacer. Transmission electron microscopy of the multilayer structure of CPP-SVs showed that the atomically flat layered structure was maintained after the annealing.     

Influence of Ga+ ion irradiation on the magnetisation reversal process and magnetoresistance in CoFe/Cu/CoFe/IrMn spin valves

Ga+ion irradiation is performed on the surfaces of IrMn-based spin valves and the effects of ion irradiation on the magnetisation reversal process and magnetoresistance(MR) are investigated.The results show that the exchange bias field and magnetoresistance ratio of the spin valve decrease with the increase of ion dose.The width of the forward step between the free layer and the pinned layer becomes gradually smaller with the increase of ion dose whilst the recoil step tends to be narrower with ion dose increasing up to 6×10 13 ions/cm 2 and the step disappears afterwards.Two peaks in the R-H curve are found to be asymmetric.     

一种非连续纳米氧化层自旋阀的显微结构研究

利用高分辨电子显微学方法(HREM)研究了纳米氧化层镜面反射自旋阀多层结构Ta(35nm)Ni80Fe20(2nm)Ir17Mn83(6nm)Co90Fe10(15nm)NOL1Co90Fe10(2nm)Cu(22nm)Co90Fe10(15nm)NOL2Ta(3nm).该自旋阀的巨磁电阻(GMR)效应高达15%,较无此镜面反射纳米氧化层(NOL)的自旋阀提高近1倍,同时交换偏置场亦有所增强.高分辨显微结构分析表明,介于钉扎层与被钉扎层之间的氧化层(NOL1)并未完全氧化,即除氧化过程生成的CoFe氧化物 关键词： 自旋阀 纳米氧化层 高分辨电子显微学 巨磁电阻效应     

Effect of thermal-annealing on the magnetoresistance of manganite-based junctions

Thermal-annealing has been widely used in modulating the oxygen content of manganites. In this work, we have studied the effect of annealing on the transport properties and magnetoresistance of junctions composed of a La0.9Ca0.1MnO3＋6 film and a Nb-doped SrTiO3 substrate. We have demonstrated that the magnetoresistance of junctions is strongly dependent on the annealing conditions： Prom the junction annealed-in-air to the junction annealedin-vacuum, the magnetoresistance near 0-V bias can vary from ～-60% to N～0. A possible mechanism accounting for this phenomenon is discussed.     

Effect of interface number on giant magnetoresistance

Ni(Cu)/Cu, Co(Cu)/Cu, and Ni-Co(Cu)/Cu multilayers with a varied number of interfaces (i.e. bi-layers) were electrodeposited on gold coated quartz discs in a flow channel cell by a potentiostatic dual-pulse plating method. It was found that the giant magnetoresistance of these multilayers increased almost linearly with increase in the number of interfaces. This result confirms that the interfaces play a dominating role in giant magnetoresistance. Comparable samples of these three types of multilayers were prepared under identical electrochemical conditions from appropriate baths. The result showed that Ni-Co(Cu)/Cu multilayers exhibited much higher giant magnetoresistance than Ni(Cu)/Cu, and Co(Cu)/Cu multilayers, which was possibly due to the structural differences between the multilayers.     

Interactive effect of impurities on giant magnetoresistance of Co–Fe/Cu multilayers

Giant magnetoresistance of Co–Fe–B/Cu multilayers fabricated in the sputtering atmosphere, where the amount of oxygen impurity is varied, is discussed in connection with their interfacial roughness. The magnetoresistance (MR) ratio of Co–Fe/Cu multilayers is enhanced by up to 33% when the oxygen content is varied between 10 and 100 ppm of processing Ar gas. The enhancement of the MR ratio was due to the flattening effect of impurity oxygen on the multilayer interfaces: the root mean square roughness of the multilayer was decreased from 7.5 to 5 Å. With increasing boron content in Co–Fe layers, however, the enhancing effect of MR ratio by oxygen diminished and nearly vanished for 12 at%-B–(Co–Fe) case. The strong affinity of boron for oxygen is suggested as a probable mechanism.     

Temperature dependence of giant magneto-resistance in PtMn- and Fe2O3-based specular spin valves

Temperature dependence of the giant magneto-resistance (MR) was measured for spin valves with and without nano-oxide layer (NOL). In spin valves with NOL, the MR ratio increased more remarkably on lowering the temperature than in those without NOL. The temperature dependence of MR ratio and that of the resistivity were explained by using two-current model. The MR ratio enhanced with NOL is attributed to the increase of the mean free path of up-spin electrons.     

Geometrical frustration, spin ice and negative thermal expansion – the physics of underconstraint

The idea that some systems could have a thermodynamically large number of accessible ground states was presaged in the work of Pauling on ice (Pauling, Cornell University Press, Ithaca, NY, 1945) [1]. With the advent of spin glasses, the methodology for describing ground states changed dramatically, and in particular it was realized that the observed slow dynamics were due to relaxation among a large number of nearly degenerate ground states. Now the accepted wisdom is that both “frustration”, as well as structural disorder, is responsible for spin glass behavior. However, well before spin-glasses were identified as a distinct class of systems, it had been appreciated that even for structurally periodic systems, bond frustration could lead to a thermodynamically large number of states. There is now a well-defined class of magnets which display effects of macroscopic ground state degeneracy. This class of geometrically frustrated magnets presents some new paradigms with which to view condensed matter systems – marginal underconstraint and downward shift of spectral weight. We discuss possible realizations of these phenomena in both in spin ice and also outside the context of local-moment magnetism.     

Enhancing low-field magnetoresistance of La0.67Ca0.33MnO3 films deposited on anodized aluminium-oxide membranes

In this paper we report a new method to fabricate nanostructured films, La0.67Ca0.33MnO3 （LCMO） nanostructured films have been fabricated by using pulsed electron beam deposition （PED） on anodized aluminium oxide （AAO） membranes, The magnetic and electronic transport properties are investigated by using the Quantum Design physics properties measurement system （PPMS） and magnetic properties measurement system （MPMS）. The resistance peak temperature （Tp） is about 85 K and the Curie temperature （To） is about 250 K for the LCMO film on an AAO membrane with a pore diameter of 20nm. Large magnetoresistance ratio （MR） is observed near Tp. The MR is as high as 85% under 1 T magnetic field. The great enhancement of MR at low magnetic fields could be attributed to the lattice distortion and the grain boundary that are induced by the nanopores on the AAO membrane.