Dot arrays of Co-Pt with a dot density of 1 Tdot/in2 were fabricated using electron beam writing. Low-energy ion etching was used to prevent the dots from deteriorating the magnetic properties. We found from the magnetic properties measured using x-ray magnetic circular dichroism that etching with low-energy ions not only caused little damage to the magnetization but also that the anisotropy field of the dots resulted in high coercivity. These results demonstrate the effectiveness of etching with low-energy ions to achieve bit-patterned media with an areal density of 1 Tbit/in2. Furthermore, the magnetic dot array with a dot period of 25 and 30 nm was fabricated by electron beam writing and etching with low-energy ion. Coercivity of these dot arrays was found to be more than 5kOe.

We developed a micro-magnetometry with a 2.5μm spatial resolution based on micro X-ray magnetic circular dichroism (XMCD) technique in order to study magnetic properties of dot arrays for bit-patterned media. This micro-magnetometer was applied to the magnetic characterization of Co–Pt dot arrays fabricated by ion beam etching. As the dot size became small, the intensity of XMCD drastically decreased for dots fabricated by Ga-focused ion beam. This suggested that the dot edges were damaged magnetically by implantation of Ga ions. The damaged width of the dot edge was estimated to be about 13nm from the decrease in XMCD intensities. This damaged edge width agreed with the ion-implanted area estimated by Monte-Carlo simulation. The less-damaged effect of Ar ion etching was verified by the XMCD measurement of Co–Pt dots with diameter of 20 and 70nm. It was concluded that ions with inertness, lower energy and smaller atomic number should be used to fabricate dot arrays with an areal density of 1Tbit/in2.

The transfer function of magnetic force microscope (MFM) tips using an exchange-spring trilayer composed of a centered soft magnetic layer and two hard magnetic layers was calculated and the resolution was estimated by considering the thermodynamic noise limit of an MFM cantilever. It was found that reducing the thickness of the centered soft magnetic layer and the magnetization of hard magnetic layer are important to obtain high resolution. Tips using an exchange-spring trilayer with a very thin FeCo layer and isotropic hard magnetic layers, such as CoPt and FePt, are found to be suitable for obtaining a resolution less than 10nm at room temperature.