Structure And Magnetic Properties Of The Antidot Arrays Film

In the past a few years, the areal density in magnetic storage media increase at a very high rate, and the highest record density is 180Gb/in² now. Recently, the candidates of ultra-high-density magnetic storage media, such as magnetic nanowire arrays, magnetic nanoparticles, magnetic dots and antidot arrays, have attracted much attention. When the bit sizes are reduced to increase the areal density, the individual grains composing the media will eventually become so small that they will no longer be thermally stable. With the development of nano-technology, recently it is found that the magnetic antidot array system can be used as a high-density record media. Because the continuity that is similar with the thin film results in an absence of superparamagnetic effect, anitdot arrays have been much investigated. It has triggered all kind of experimental studies on this system. Magnetic antidot arrays film deposited in self-assembled alumina templates has a high porosity, which can be used for a high areal density media. The microstructures, micro and macro magnetic properties were investigated systematically by Field Scanning Electron Microscope, X-ray diffraction, Conversion electron Mossbauer spectroscopy, magnetic property measurement system and high frequency measurement. The main contents are as follows:1. The magnetic moment distribution of the Fe antidot arrays was obtained by CEMS, and the magnetic moment component perpendicular to the film plane was found. The magnetic moment distribution can be characterized as a cone-shaped model, which agrees well with the experiment results.2. The temperature dependence of the coercivity and remnant magnetization of Fe antidot array film shows increase with decreasing of the temperature. The free energy barrier will be mainly affected by the thermal excitation. The magnetic irreversibility is obtained by the zero field and field cooling magnetization curve (ZFC-FC), which is caused from the energy barrier by the pinning effect of the holes.3. The temperature dependence of the coercivity of Co antidot array film shows an obvious maximum around 50 K. When the temperature is over 50 K, the coercivity is mainly determined by the magnetocrystalline anisotropy. While the temperature is in the range of 5-50 K, pinning effect also play an important effect on the coercivity. The competition between the magnetocrystalline anisotropy and the pinning effect leads to an abnormal temperature dependence.4. The formation of effective uniaxial anisotropy and decrease of coercivity of the Co/Fe₅₀Mn₅₀ bilayer films induced by the antiferromagnetic FeMn covering layer. It is found that quasi-unidirective exchange interaction can be responsible for the uniaxial anisotropy after magnetic heat treatment.5. The exchange bias (H_E) and coercivity (H_c) of the FeMn/Co/FeMn multilayer antidot array film by sputtering on the porous alumina templates strongly depend on the temperature. H_E shows a transition from negative to positive for the antidot array film with increasing temperature. This result can be explained by the decreasing of the exchange coupling energy due to the existence of the hole in the antidot array film.