High coercivity in ultrathin epitaxial micrometer-sized particles with in-plane magnetization: Experiment and numerical simulation

Arrays of 2.5×10⁷ ultrathin epitaxial W(110)/Fe(110)/W(110) submicron particles with in-plane magnetization were fabricated using x-ray lithography and dry-etching techniques. A large coercive-field increase as compared to continuous films is observed which is ascribed to the short range of self-demagnetizing fields for ultrathin particles with in-plane magnetization. A method to extract the mean hysteresis loop of a single particle and the coercive field distribution function from measurements over the whole array is proposed. The analysis is in good agreement with the picture of single-domain particles and of nucleation volumes much smaller than particle dimensions. It is corroborated by micromagnetic calculations performed on isolated ideally square particles.