Fully epitaxial Co₂Fe_xMn_1−xSi(CFMS)/Ag/Co₂Fe_xMn_1−xSi current-perpendicular-to-plane giant magnetoresistive devices with various Fe/Mn ratios x and top CFMS layer thicknesses t_CFMS were prepared. The highest magnetoresistance (MR) ratios, 58% at room temperature and 184% at 30 K, were observed in the sample with x = 0.4 and t_CFMS = 3 nm. Enhancement of interface spin-asymmetry was suggested for x = 0.4 compared with that at x = 0. A MR ratio of 58% was also observed even in a very thin trilayer structure, CFMS(4 nm)/Ag(3 nm)/CFMS(2 nm), which is promising for a next-generation magnetic read sensor for high-density hard disk drives.

Thin films of oriented island-like crystallites of ${\text{L1}}_0$ FePt separated by amorphous $\mathrm{(a-)}{\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ were fabricated. The process took advantage of the overgrowth of α-Fe on Pt “seed” particles epitaxially grown on (100) NaCl and MgO substrates and the ordering reaction between Fe and Pt upon annealing at temperatures higher than 500 °C. The coercivities of the annealed (600 °C for 6 h) $\mathrm{a-}{\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{/Fe(1 nm)/Pt}$ (1.5 nm) films on both the NaCl (100) and MgO (100) substrates are higher than 3.3 kOe. Transmission electron microscopy observation showed that the film consisted of oriented ${\text{L1}}_0$ FePt island-like crystals with an average size of 12 nm and a separation of 4 nm. It was found that any one of the three 〈100〉 axes of the fcc Pt parent particles could act as the tetragonal c axis of the ${\text{L1}}_0$ FePt superstructure and all three-variant ordered crystalline domains of the tetragonal ${\text{L1}}_0$ phase could exist in the small 10-nm-size FePt crystallites. The high magnetic coercivity of the film, with well-separated FePt particles, can be attributed to the ordering ${\text{(L1}}_0)$ as well as the oriented nature of the FePt crystallites.