Temperature dependence of the energy barrier and switching field of magnetic islands with perpendicular anisotropy

摘要

Using the highly sensitive anomalous Hall effect (AHE) we have been able tomeasure the reversal of a single magnetic island, of diameter 220nm, in anarray consisting of more than 80 of those islands. By repeatedly traversing thehysteresis loop, we measured the thermally actuated fluctuation of theswitching field of the islands at the lower and higher ends of the switchingfield distribution. Based on a novel easy-to-use model, we determined theswitching field in the absence of thermal activation, and the energy barrier inthe absence of an external field from these fluctuations. By measuring thereversal of individual dots in the array as a function of temperature, weextrapolated the switching field and energy barrier down to 0K. Theextrapolated values are not identical to those obtained from the fluctation ofthe switching field at room temperature, because the properties of the magneticmaterial are temperature dependent. As a result, extrapolating from temperaturedependent measurements overestimates the energy barrier by more than a factorof two. To determine fundamental parameters of the energy barrier betweenmagnetisation states, measuring the fluctuation of the reversal field at thetemperature of application is therefore to be preferred. This is of primaryimportance to applications in data storagea and magnetic logic. For instance infast switching, where the switching field in the absence of thermal activationplays a major role, or in long term data stability, which is determined by theenergy barrier in the absence of an external field.