The effect of the in-plane demagnetizing field on films with weak perpendicular magnetic anisotropy

Abstract

The effect of reduced lateral dimension on the magnetic behavior of long microstrips with weak perpendicular magnetic anisotropy has been studied. The hysteresis loops of the surface and the whole volume of microstrips and large films have been recorded by magneto-optic Kerr effect magnetometry and vibrating sample magnetometry. Also, the magnetic structure of the microstrips and its evolution under an applied field have been studied by magnetic force microscopy and the Bitter technique. It has been observed that the transversal dimension of the microstrips gives rise mainly to an in-plane demagnetizing field which affects their hysteresis loops and magnetic structure in a different manner. A great increase in the surface coercivity in the transversal direction of the microstrips is the main unexpected effect that has been observed. On the other hand, the magnetic structure in remanence and its evolution with increasing thickness have not revealed a significant dependence on the direction of the last saturating field. It has also been observed that the reduced size of the microstrips in their transversal direction does not prevent the occurrence of the property known as rotatable anisotropy, typical of films with stripe domain structure, although it makes this property very anisotropic. Finally, a two-dimensional qualitative model of closed flux stripe domain structure has been used for correlating the enlargement of the surface coercivity of the microstrips with the evolution of their magnetic structure.