The Study Of L1₀-FePt-based Perpendicular Exchange Coupled Composite Films With Synthetic Antiferromagnetic Structure

Recently, the drastic information urgently require increasing information storage capacity of recording system. Up to now, among the various information storage technologies, hard disk drive (HDD) is the most important way for high capacity storage. 1Tb/in2 areal density is the limitation of current recording media due to superparamagnetism. As a new generation material for the high density magnetic recording media, L10-FePt ordered alloys have high uniaxial magnetocrystalline anisotropy constant (107erg/cc) and very small thermal stable grain size(3～5nm). It can realize 1 OTb/in2 ultra-high areal recording density. To solve the problems between thermal stability and writability, exchange coupled composite (ECC) media is proposed and becomes a hot research. Among the research of ECC media, different soft materials were used as soft region,such as Fe、[Co/X](X=Ni、Pt)multilayers etc, which decreases the coercivity and keeps the thermal stability. However, in order to obtain small enough coercivity of ECC media, the thickness of soft region must increase, which deteriorates the thermal stability and broadens the switching field distribution(SFD).To solve the problems, a new modified antiferromagnetic exchange coupled composite (AFC-ECC) has been proposed, namely, ECC element is antiferromagnetically coupled with soft material. In this paper, a synthetic antiferromagnetic exchange coupled sandwich structure is coupled with FePt to realize the structure. We take a lot of work on property study of L10-FePt based perpendicular AFC-ECC films.Firstly, synthetic antiferromagnetic [Co/Ni]N/Ru/[Co/Ni]M are used to couple with FePt to prepare FePt/[Co/Ni]N/Ru/[Co/Ni]M films. Among the composite films, the coercivity oscillates with the Ru thickness. When there is an antiferromagnetic exchange coupling between FePt/[Co/Ni]N and [Co/Ni]M, the coercivity of film is minimal. The reduction of coercivity is also related to the thickness of [Co/Ni]N multilayer. Furthermore, the introduction of an antiferromagnetic coupling leads improvement of thermal stability and narrowing of SFD. High tolerance of switching field angular-dependence also is observed in composite films.Secondly, magnetic reversal mechanism of AFC-ECC structure is studied. Through the measurement of reversal curves and magneto-resistance, it is founded that the magnetic reversal process of composite structure varies with Ru thickness. In the antiferromagnetic case, the magnetization reversal of [Co/Ni]M promotes the magnetic moment rotation of [Co/Ni]N,and then leads the magnetization reversal of FePt/[Co/Ni]N. Finally, we study the magnetization reversal process in details through micromagnetic simulation, which shows that the introduction of antiferromagnetic coupling enhances the magnetization reversal of AFC-ECC structure.