ABSTRACT
Following the tendency of the miniaturization of active elements for magnetic sensors, the MOKE investigation of the magnetization reversal has been performed in Fe-rich nanometric amorphous wires (nominal composition Fe72.75Co2.25B15Si10).First, the arrays of glass-covered microwires (radius of metallic nucleus 500 nm) have been studied by magnetic. The result of PPMS magnetic (four-nano-wire array) experiments is presented in Fig. 11.1. The clear jumps of magnetization could be observed in volume. These jumps are related to the giant Barkhausen jumps associated with the magnetization reversal in single microwire as a consequence of the interaction between the microwires. Based on the obtained results, we can conclude that the magnetic behavior of the glass-covered wires with such extremely tiny diameter remains magnetically bistable and could be considered in the frame of the core-shell model.Second, the arrays of glass-covered nano-wires (radius of metallic nucleus 500 nm) have been studied by magneto-optical techniques (Fig. 11.2). During the experiment, the array of 10 wires has been rotated in the plane perpendicular to the plane of the light. The results of longitudinal experiments are presented in Figs. 11.3 and 11.4.
Figure 11.4 Dependencies of the switching fields H1 on angle Φ.The clear jumps of magnetization could be observed in surface hysteresis loops (Fig. 11.3). These jumps are related also, as for the case of volume loops, to the giant Barkhausen jumps associated with the magnetization reversal in single microwire as a conse-quence of the interaction between the microwires.Although the array contains 10 wires, there are only two jumps in the MOKE hysteresis loop. This means that in these experiments the collective jumps of some number of wires take place. For example, six microwires change the direction of the magnetization during the first jump and then four microwires change the direction of the magnetization during the second jump. This behavior could be explained by the very narrow distribution of the switching field in the studied microwires.Figure 11.4 presents the angle Φ dependence of the switching fields H1. As it is possible to see, the Barkhausen jumps take place up to the angle Φ of about 80°. This means that the bistability effect exists for the almost perpendicular direction of the microwire to the external magnetic field. Analyzing the angle dependence of the first jump, we have constructed the dependence H1* /cos (Φ) (white quadratic points), where H1* is the value of the switching field for the angle Φ = 0. Also, we have constructed the dependence H1 cos (Φ) (white triangle points).For the simplest case, when only the projection of the external magnetic field on the wire axis causes the magnetization reversal,
