A Controllability Investigation of Magnetic Properties for FePt Alloy Nanocomposite Thin Films

An appropriate writing field is very important for magnetic storage application of L10 FePt nanocomposite thin films. However, the applications of pure L10 FePt are limited due to its large coercivity. In this paper, the ratios of L10 and non-L10 phase FePt alloy nanoparticles in FePt/MgO (100) nanocomposite thin films were successfully tuned by pulsed laser deposition method. By adjusting the pulsed laser energy density from 3 to 7 J/cm2, the ordering parameter initially increased, and then decreased. The highest ordering parameter of 0.9 was obtained at the pulsed laser energy density of 5 J/cm2. At this maximum value, the sample had the least amount of the soft magnetic phase of almost 0%, as analyzed by a magnetic susceptibility study. The saturation magnetization decreased with the increase in the content of soft magnetic phase. Therefore, the magnetic properties of FePt nanocomposite thin films can be controlled, which would be beneficial for the magnetic applications of these thin films.

Fabrication and characterization of magnetic FePt nanoparticles prepared by extraction–pyrolysis method

In the present work, possibilities of the extraction–pyrolysis method (EPM) to produce FePt nanoparticles with the face-centered tetragonal (fct) phase were studied. A mixture of fine-disperse powder of carbonyl iron and n-trioctylammonium hexachloroplatinate [(С8Н17)3NH]2PtCl6 solution in toluene, preliminary produced by the solvent extraction method, is used as a precursor. Precursors with a different molar ratio of metals were used. The performed investigations show that as a result of pyrolysis in the air (Tpyr = 600°C, tanneal = 30 min), a FePt alloy with the fct phase is produced. Moreover, such phases as FePt3 and/or Fe3Pt with the cubic structure may be also present in the final products. The phase composition of the produced samples depends on the Fe:Pt molar ratio in the precursor. An increase of the fct phase part with the growth of the iron content from 40 to 60 mol% is observed. Also, with the Fe80%Pt20% molar ratio of the metals in the precursor, only the ordered fct phase along with a small amount of hematite and iron chloride exists in the produced sample. Magnetic measurements confirm the fct-FePt phase formation in all produced samples and evidence that the coercivity exceeds the value (3 kOe) at the 50 mol% Fe concentration in the precursor and significantly decreases with increasing the Fe concentration to 80 mol%.

First-principles calculations of perpendicular magnetic anisotropy for spintronic applications

A combination of density functional theory and non-equilibrium Green’s function methods are used to simulate spin-dependent electronic transport in monatomic Au-nanowires sandwiched between ferromagnetic electrodes. Electrodes of the junction are in turn composed of tetragonal FeCo, FePd and FePt alloys. Magnetic anisotropy energies of the electrodes are calculated for different values of the c/a ratios of the electrode lattice constants and it is shown that at c/a = 1.05, the FePt electrodes gain a relatively large amount of magnetic anisotropy energy (MAE). Hence, it is concluded that the ferromagnetic FePt alloy can be used as a suitable type of electrode for applications in perpendicular magnetic tunnel junctions (MTJs). We observe that increasing the c/a ratio leads to notable improvements in the spin filtering of the FeCo and FePd MTJs while it only has a slight effect on the filtering of the FePt MTJ. Later, we show that by removing the interfacial Pt atoms of the FePt MTJ, we are able to enhance its filtering property.