Experimental realization of graded $L1-FePt/Fe$ composite media with perpendicular magnetization

A concept is suggested and experimentally realized to fabricate graded media for ultrahigh density magnetic recording where the material parameters vary gradually in the interfacial region between the hard magnetic part and the soft magnetic part of epitaxial $L10-FePt/Fe$ exchange spring nanocomposites with perpendicular magnetization. A graded interface between the $L10-FePt$ phase and the Fe phase is formed by depositing part of the Fe layer at elevated temperatures. The existence of the graded interface is verified by electron energy-loss spectroscopy. The influence of the character of the graded interface on the magnetic properties is studied. With increasing thickness of the graded interface the coercivity continuously decreases, which can be used for a fine tuning of the coercivity of exchange spring composite media.