Temperature dependence of Barkhausen Jumps in hysterisis loops of permalloy Ni₀Fe₂₀
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This thesis studies the temperature dependence of Barkhausen Jumps (BJ) using the Magneto-Optical Kerr effect (MOKE). Both positive and negative jumps are analyzed at different temperatures. Measurements and analysis of positive jumps and negative jumps at room temperature (300 K) and low temperature (110 K) are described. The jump-amplitude critical exponent of the negative jumps (about 2.1) is observed to be bigger than that of positive jumps (about 1.6) and for positive jumps the exponent does not depend on temperature. The negative jump exponent measured at low temperature is bigger than at room temperature. The coercive force Hc becomes bigger when the temperature is reduced. We also show that the negative jumps are probably not caused by thermal activation but are most likely a consequence of the limited area covered by the beam spot. A next Generation experiment, based on two laser beams that simultaneously probe small and large overlapping regions of the sample is proposed to resolve the origin of non-thermally activated negative BJs.