Y. J. Tang

A method for fabricating nanopatterned media has been investigated. A monolayer of regularly distributed Ni nanoparticles of uniform diameter $(\sim 5\mathrm{nm})$ fabricated on the surface of a polyimide-coated Si substrate using metal film-polyamic acid interactions was utilized as a protruding template to deposit an array of FePt phase. A FePt film (5 nm thick) was sputtered onto this template with or without an underlayer of either 5-nm-thick MgO or CoO and analyzed before and after annealing. It was observed that while the FePt films sputtered on flat Si substrates with underlayers exhibited low $H_c$ of only about 1 kOe after the $L{1}_0$ conversion, the FePt samples deposited onto protruding Ni nanoparticle templates showed a significant increase in $H_c$ to $\sim 8.1\mathrm{kOe}$ . The FePt sample with CoO underlayer exhibited a possibly strong perpendicular magnetic anisotropy. The intergranular exchange coupling of the samples was also investigated by using $\Delta M$ method.

The relationship between magnetic properties and microstructure of thin antiferromagnetic CoO layers in $\{\mathrm{CoO}\mathrm{}\left(X\right)/{\mathrm{SiO}}_2\left(50\mathrm{}\AA \right){\}}_{25}$ multilayers has been investigated. The temperature decay of the thermoremanent moment, zero-field-cooled/field-cooled magnetization measurements, and specific heat were evaluated as indicators of the magnetic ordering temperature. The temperatures associated with each decreased slightly with decreasing CoO layer thickness from 100 to 30 Å, but then exhibited a sharp decrease for CoO layer thickness below 20 Å. This decrease has been previously observed, and was attributed to intrinsic finite size effects associated with broken magnetic bonds at the surfaces. In the present investigation, it was determined that the CoO layer was amorphous in these thinner layers, accounting for the dramatic drop in Néel temperature. For thicker CoO layers, all measures of magnetic ordering coincide, indicating a true Neel temperature, whereas they do not for the thinner films. The structural change of CoO from crystalline to amorphous also causes a significant change in the temperature dependence of the magnetization, due to an increased number of weakly coupled uncompensated spins.

The TbCo/Si multilayers prepared by the rf magnetron sputtering system with various Si thickness have been investigated. X-ray diffraction, magnetic measurement and Kerr rotation have been performed. No antiferromagnetic coupling was found for the system. With the thickness of Si layer $t_{\mathrm{Si}}$ increasing, the perpendicular anisotropy constant $K_u,$ and the saturation magnetization $M_s$ decreased rapidly. It was assumed that ${\mathrm{Co}}_{\mathrm{2}}\mathrm{Si}$ and Tb had been formed in the interfacial zone between TbCo and Si layers due to the interlayer diffusion. The decreasing of $M_s$ is attributed to the decreasing of the effective thickness of magnetic layer.