High magnetic coercivity of FePt–Ag/MgO granular nanolayers

Highligts• The role of Ag atom in reduction of transition to L1₀ phase temperature has been determined. • The effect of Ag presence on FePt nanoparticles coercivity was observed. • VSM results of 10 nm nanoparticles show that coercivity has increased up to 1.4 T. • Ag gradually form nano scale clusters with separate lattice and FePt-Ag nanocomposite appears. L1₀-FePt ferromagnetic nanoparticles have a hight coercivity of Tesla order. Thus, these nanoparticles, with size of 10 to 15 nm and uniform surface distribution, are suitable in magnetic data storage technology with density of more than 1GB. In order to improve structural and magnetic properties of FePt nanoparticles, some elements and combinations have been added to compound. In this research, we show that due to the presence of the Ag, the phase transition temperature of FePt from fcc to L1₀-fct phase decreases. The presence of Ag as an additive in FePt–Ag nanocomposite, increases the magnetic coercivity. This nanocomposite, with 10% Ag, was deposited by magnetron sputtering on the MgO heat layer. VSM results of 10 nm nanoparticles show that coercivity has increased up to 1.4 T. XRD and FESEM results confirm that the size of the L1₀-FePt nanoparticles are 10 nm and their surface distribution are uniform. Ag gradually form nano scale clusters with separate lattice and FePt–Ag nanocomposite appears. The result of this process is emptiness of Ag position in FePt-fcc lattice. So, the mobility of Fe and Pt atoms in this lattice increases and it can be possible for them to move in lower temperature. This mechanism explain the effect of Ag on decreasing the transition temperature to fct-L1₀ phase, and hight coercivity of FePt nanoparticles.