6 Experimental Results 6.4 Microwave assisted switching in Ni81Fe19 elements

Microwave assisted switching is a promising way to control the switching field in a magnetic switching process of small structured elements. Thirion et al. [1] first demonstrated the reduc-tion of the switching field of single Cobalt nano-particles by applying short microwave pulses in a micro-SQUID experiment. For future industrial application it is of high importance to trans-fer this technique to patterned elements. A microwave field is expected to reduce the switching field in these elements even for the case in which the switching process is dominated by domain nucleation and growth. The magnetization vector oscillates with a large precession angle if the resonance condition is fulfilled. This reduces the effective energy barrier for domain nucleation, which otherwise cannot be crossed by thermal fluctuations alone. We studied the quasi-static switching behavior of a Ni81Fe19 ellipsoid under the influence of a mi-crowave field by magneto-optic Kerr effect magnetometry in longitudinal geometry. A picosecond diode laser with a wavelength of 407nm and a pulse width of 73ps is employed. The sample is placed on top of a impedance matched microwave antenna with a width of 430µm. The magnetic material of the sample is facing the antenna to achieve a larger microwave field. The long axis of the ellipsoid is parallel to the quasi-static magnetic field generated by external coils, and th