Perpendicular giant magnetoresistance of magnetic multilayers

The theoretical and experimental studies of the giant magnetoresistance effect in metallic magnetic multilayers with measuring current perpendicular to the interface planes are reviewed. Theoretical formalisms of electronic transport in the inhomogeneous electron gas are critically compared with emphasis on the perpendicular magnetoresistance in multilayers. The effects of interface roughness, potential steps at the interfaces, and realistic band structures are addressed. The experimental determination of the perpendicular resistance of metallic multilayers requires either low-resistance measurement techniques or microfabricated samples with enhanced resistances. The experimental methods known at present are discussed and, where possible, compared with each other.     

Giant magnetoresistance of Co/ITO multilayers

The electrical and magnetic properties of Co/ITO multilayers with various ITO layer thickness are studied. Negative giant magnetoresistance with a maximum of −1.9% at room temperature and −2.57% at 15 K are observed. The magnitudes of GMR oscillate with a period of about 1 nm when varying the thickness of ITO layer.     

自旋阀中的各向异性磁电阻效应

采用平面霍尔效应测量方法，对Ta(8nm)/NiFe(7nm)/Cu(24nm)/NiFe(44nm)/FeMn(14nm)/Ta(6nm)自旋阀多层膜进行了研究.结果表明，在样品中存在着自由层和被钉扎层之间的各向异性磁电阻的“混合”效应.与通常所采用的磁电阻测量方法相结合，平面霍尔效应的测 量可以给出自旋阀中各向异性磁电阻以及自由层和被钉扎层的磁矩随外场变化的更多信息. 关键词： 自旋阀 各向异性磁电阻 平面霍尔效应     

Universal relationship between giant magnetoresistance and anisotropic magnetoresistance in spin valve multilayers

We measure the giant magnetoresistance (GMR) with the current both parallel and perpendicular to the direction of the magnetization in the ferromagnetic (FM) layers and thus probe the anisotropy of the effective mean free paths for the spin-up and spin-down electrons, seen in the anisotropic magnetoresistance. We find that the difference of the GMR in the two configurations, when expressed in terms of the sheet conductance, displays a nearly universal behavior as a function of GMR. On interpreting the results within the Boltzmann transport formalism we demonstrate the importance of bulk scattering for GMR.     

Antisymmetric magnetoresistance in magnetic multilayers with perpendicular anisotropy

While magnetoresistance (MR) has generally been found to be symmetric in applied field in nonmagnetic or magnetic metals, we have observed antisymmetric MR in Co/Pt multilayers. Simultaneous domain imaging and transport measurements show that the antisymmetric MR is due to the appearance of domain walls that run perpendicular to both the magnetization and the current, a geometry existing only in materials with perpendicular magnetic anisotropy. As a result, the extraordinary Hall effect gives rise to circulating currents in the vicinity of the domain walls that contributes to the MR. The antisymmetric MR and extraordinary Hall effect have been quantitatively accounted for by a theoretical model.     

An analytic approach to tunnelling magnetoresistance

We present an analytic model for the barrier transmission coefficient that can be used to calculate the tunnelling magnetoresistance (TMR) for metal-insulator-metal systems. It removes the approximations inherent in the Simmons’ and Brinkman models currently used to fit experimental systems that give much lower predictions of the barrier height than would be expected. The model is accurate enough to directly relate to the experiment and hence device optimisation by predicting junction parameters that are in line with bulk properties.     

Role of interface scattering on the giant magnetoresistance of magnetic multilayers

A discussion is presented of the effect of interface scattering on the giant magnetoresistance of magnetic multilayers. It has recently been found experimentally that increased interface scattering causes the magnetoresistance to increase for Fe/Cr multilayers, but to decrease for Co/Cu multilayers. An explanation is proposed for this striking difference in behaviour for these two systems.     

Mean free path effects on the current perpendicular to the plane magnetoresistance of magnetic multilayers

We have carried out an experimental and theoretical study of the magnetoresistance MR(H) in the CPP (current perpendicular to the planes) mode for two types of magnetic multilayers that differ only in the ordering of the magnetic layers: [Co(10 A)/Cu(200 A)/Co(60 A)/Cu(200 A)](N) and [Co(10 A)/Cu(200 A)](N)[Co(60 A)/Cu(200 A)](N). The series resistor model predicts that in the CPP mode MR(H) is independent of the ordering of the layers. Nevertheless, the measured MR(H) curves were found to be completely different for the two cases. Calculations based on a realistic band structure and the Kubo formula show that the results are a consequence of a long mean free path.     

Anomalous temperature dependence of the magnetoresistance in Co/Cu multilayers

An anomalous temperature dependence of magnetoresistance (MR) of Co/Cu multilayer films witha ～3 Å thick magnetic layer has been established experimentally. The temperature of the MR maximum T _max is shown to coincide with the Néel temperature. The variation of T _max with the Cu layer thickness follows an oscillatory pattern.     

Magnetic property and magnetoresistance in Fe/ITO multilayers

Giant magnetoresistance was found in DC magnetron sputtering Fe/ITO multilayers. The magnetic properties, electrical properties and magnetoresistance were investigated. A critical temperature is found around 50 K where the temperature dependence of resistivity and magnetoresistance ratio exhibit an abruptly change. The temperature dependence of resistance is found to obey Mott's 1/4 law for low temperature. The max magnetoresistance ratio of 2.0% and 6.7% is found at room temperature and 12.5 K, respectively. The increase of magnetoresistance ratio at low temperature is due to the decrease of spin-mixing effect.     

Giant magnetoresistance and magnetothermopower in Co/Cu multilayers

The thermopower (Seebeck coefficient, S) has been measured on a series of Co/Cu multilayers that exhibit giant negative magnetoresistance (GMR). Negative in zero applied field, S(H) increases in magnitude as the field is increased, approaching that of bulk Co. The change in S is inversely proportional to the resistance of the sample which is, in turn, proportional to the square of the magnetization. A model is presented that yields both the GMR and S(H) from the spin-split density of states of the Co without the need of a spin-dependent scattering potential at the interfaces.     

Current-perpendicular (CPP) magnetoresistance in magnetic metallic multilayers

We present an experimentalist's view of the theory and published data for the magnetoresistance (MR) of a multilayer composed of alternating ferromagnetic (F) and non-magnetic (N) metals measured with current flow perpendicular to the layer planes (CPP-MR). We explain the advantages of this geometry for determining the fundamental quantities underlying spin-polarized transport, describe the different techniques developed to measure the CPP-MR, summarize the salient features of the models used to analyze experimental data, and describe tests of those models. We then review what has been learned so far about spin-dependent scattering anisotropy and spin relaxation in F-metals and at F/N interfaces, specific resistances of F/N interfaces, the temperature dependence of spin-polarized transport parameters, and mixing of the spin-polarized electron currents. After a brief overview of some new directions, we conclude with a list of questions still to be answered.     

Effects of interfacial roughness on the magnetoresistance of Co/Cu multilayers

Using a semi-classical approach, Hood, Falicov and Penn have studied the effects of interfacial roughness on the magnetoresistance (MR) of iron based trilayers (Fe/Cr/Fe and Fe/Cu/Fe). We extend their theory to magnetic metallic multilayers composed of N bilayers ferromagnetic-normal metal. The in plane MR of Co/Cu multilayers is calculated for correlated quasiperiodic interfaces. The averaged effects due to impurities, interdiffusion, band structure, etc. are included in a simple way using two phenomenological parameters S^↑ and S^↓ for two directions of spin. MR variation with S^↑, S^↓ and relaxation time is reported. We analyse also recent experimental data giving the influence of number of bilayers on the MR of Co/Cu multilayers for different temperatures.     

Fe/Cr磁性多层膜的制备及其磁电阻测定

利用磁控溅射制备了不同非磁性层厚度的Fe/Cr多层磁性薄膜系统,利用四探针法测定了该多层膜系统在不同磁场下磁电阻效应,用饱和场法给予佐证,溅射制备的多层膜系统饱和场明显地随Cr层厚度增加而衰减振荡,得出了Fe/Cr多层膜的铁磁反铁磁耦合的交换耦合强度随非磁性层厚度变化的物理规律.