We present results from STM based point contact measurements of the local resistance in differently shaped GMR spin-valve elements. Data from rings reveal that the magnetoresistance is linked to magnetic domain wall motion within the ring. Measurements with varying currents indicate that the current induce magnetisation reversal and lead to offsets in the magnetic field necessary for magnetisation reversal. The offsets can be attributed to current induced spin torque for the thin Py layer and erstedt field for the thick Co layer.
STM based point contact measurements is a method relatively unexplored for obtaining laterally resolved information of the magnetoresistance of spin-valve elements. Here we present a study on how this method can be used to investigate the influence of the local current and applied field on the micromagnetic structure in spin-valve elements of different shapes.
Spin-valve elements comprising elliptical discs and octagon shaped rings were prepared from multilayer (Cu/Py/Cu/Co/Cu) films and investigated in a CPP configuration. The data acquired from point contacts in ellipses compare well with the expected magnetoresistance deduced from field-dependent MFM measurements or AGM measurements on ensembles of elements.
In ring elements the magnetoresistance was probed as a function of the lateral position of the contact, the applied field and the sense current. Magnetisation reversal was observed; both as induced by changing the magnetic field and the sense current. The field induced reversals are interpreted as a consecutive rotation of the onion states of the two magnetic layers. The current induced offsets and the current induced magnetisation reversal can be interpreted as induced by a combination of the spin torque and the Øerstedt field of the injected current. For the thin magnetic Py layer (2.5 nm) the current induced torque dominates the current induced offsets in field switching, with the effect being strongest in the vicinity of the magnetic domain walls. The offsets of the thick magnetic Co layer (20 nm) are dominated by the Øerstedt field, and the effect is strongest away from the magnetic domain boundaries. The sense current induced offsets can qualitatively be explained by the domain structure of the octagons. |