The magnetoresistive effect induced by stress in spin-valve structures

Using a method of free energy minimization, this paper investigates the magnetization properties of a ferromagnetic （FM） monolayer and an FM/antiferromagnetic （AFM） bilayer under a stress field, respectively. It then investigates the magnetoresistance （MR） of the spin-valve structure, which is built by an FM rnonolayer and an FM/AFM bilayer, and its dependence upon the applied stress field. The results show that under the stress field, the magnetization properties of the FM monolayer is obviously different from that of the FM/AFM bilayer, since the coupled AFM layer can obviously block the magnetization of the FM layer. This phenomenon makes the MR of the spin-valve structure become obvious. In detail, there are two behaviors for the MR of the spin-valve structure dependence upon the stress field distinguished by the coupling （FM coupling or AFM coupling） between the FM layer and the FM/AFM bilayer. Either behavior of the MR of the spin-valve structure depends on the stress field including its value and orientation. Based on these investigations, a perfect mechanical sensor at the nano-scale is suggested to be devised experimentally.

Effect of thermal deformation on giant magnetoresistance of flexible spin valves grown on polyvinylidene fluoride membranes

We fabricated flexible spin valves on polyvinylidene fluoride（PVDF） membranes and investigated the influence of thermal deformation of substrates on the giant magnetoresistance（GMR） behaviors. The large magnetostrictive Fe_（81）Ga_（19）（Fe Ga） alloy and the low magnetostrictive Fe_（19）Ni_（81）（Fe Ni） alloy were selected as the free and pinned ferromagnetic layers.In addition, the exchange bias（EB） of the pinned layer was set along the different thermal deformation axes α_（31） or α_（32） of PVDF. The GMR ratio of the reference spin valves grown on Si intrinsically increases with lowering temperature due to an enhancement of spontaneous magnetization. For flexible spin valves, when decreasing temperature, the anisotropic thermal deformation of PVDF produces a uniaxial anisotropy along the α_（32） direction, which changes the distribution of magnetic domains. As a result, the GMR ratio at low temperature for spin valves with EB α_（32）becomes close to that on Si, but for spin valves with EB α_（31）is far away from that on Si. This thermal effect on GMR behaviors is more significant when using magnetostrictive Fe Ga as the free layer.

Interface reactions in film materials

Interface reaction (IR) is a frequently observed phenomenon in the study ofadvanced thin film materials. It is very important to study the reaction conditions at which IRhappens and then to suppress or make use of it, the necessary conditions, including boththermodynamical and dynamical conditions of IR were discussed in detail. IRs in various systems,including oxide/silicon, oxide/metal, metal/metal, metal/semiconductor andsemiconductor/semiconductor, were reviewed. Methods to suppress and make use of IR were alsointroduced.

Spin manipulations through electrical and thermoelectrical transport in magnetic tunnel junctions

A brief review is presented,which includes the direct current,alternate current,electrical and thermoelectrical transport as well as spin transfer effect in a variety of spin-based nanostructures such as the magnetic tunnel junction(MTJ),ferromagnet(FM)-quantum dot(QD)/FM-FM,double barrier MTJ,FM-marginal Fermi liquid-FM,FM-unconventional superconductor-FM(FUSF),quantum ring and optical spin-field-effect transistor.The magnetoresistances in those structures,spin accumulation effect in FM-QD-FM and FUSF systems,spin injection and spin filter into semiconductor,spin transfer effect,photon-assisted spin transport,magnonassisted tunneling,electron-electron interaction effect on spin transport,laser-controlled spin dynamics,and thermoelectrical spin transport are discussed.

A micron-sized GMR sensor with a CoCrPt hard bias

A GMR（giant magneto-resistive） spin valve sensor for magnetic recording has been designed in an attempt to solve the Barkhausen noise problem in small-sized GMR sensors.In this study,the GMR ratio of the top-pinned spin valve is optimized to a value of 13.2%.The free layer is magnetized perpendicular to the pinned layer by a CoCrPt permanent magnetic bias so that a linear magnetic field response can be obtained.An obvious improvement on performance is observed when the permanent magnetic bias is magnetized,while the GMR sensor has a steadier MR-H loop and a smaller coercive field.