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Hysteresis cycle of the heterostructure measured at , along one of the directions before processing. The lower inset shows , the magnetization of the film measured with a applied field as a function of the temperature (the data were corrected to take into account the demagnetizing factor). The upper inset shows the critical current density of the film vs temperature, as determined according to the Bean model from magnetization measurements.
Picture of the patterned microbridge. The current flows between terminals I1 and I2 and the voltage is measured between V1 and V2. The width of the bridge is .
Current–voltage characteristics measured at on the microbridge with a saw-tooth alternating current. Vector shows the current direction during the first half period. In the middle graph, (b), the magnetization of the magnetic layer is parallel to the current direction. In the upper and lower graphs, (a) and (c), the magnetization is perpendicular to the current. In these configurations the current voltage characteristics are nonsymmetric and the nonsymmetry depends on the respective directions of and . The insets are zooms of graphs (a) (solid line) and (c) (dotted line) in the vicinity of the current values for which the sample is driven from the nonresistive to the resistive states.
Interpretation of the nonsymmetry of the current–voltage characteristics. In the upper right part of the figure, the contribution of the magnetic film (solid arrows) to the vertical component of the field along the bridge edges add to that of the field created by the current flowing in the superconducting film (dotted arrows). In the lower left part the magnetic film contribution subtracts from that due to the current. Then, the current required to drive the superconducting film in the critical state is lower and the voltage measured for the same current amplitude is larger in the situation shown on the right than in that shown on the left.
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