Objective 1. Synthesis of ternary L1₀ FeCo and FeNiCo nanoparticles

The first objective is the synthesis of binary FeCo and ternary FeNiCo in the tetragonal, L1₀, crystal structure. This task is the most novel, high risk but with high gain, and will be investigated intensively. Here the big challenge is to develop a kinetic pathway to form the hard magnetic L1₀ crystal structure under reasonable conditions. Using the PI previous knowledge to synthesize, via liquid phase reactions, the FePt and CoPt nanoparticles directly to the ordered tetragonal phase without any post-annealing procedures,^{12, 13, 14} and taking into account his recent preliminary data concerning an induced tetragonal distortion through doping of the FeCo alloy with carbon, we propose the synthesis of L1₀ FeCo and FeNiCo via wet chemical approaches through studying the concentration of the ternary alloy, following the theory,¹⁰ and through doping the ternary alloys with other elements. These interstitial elements can stabilize the tetragonal structures with higher values of anisotropy because of expansion in the crystal lattice. Depending on the results achieved, (mainly from the coercive field values), doping with elements such as carbon, Bi, and Rh, will be studied. The selection of the proposed third element coming from recent theoretical studies reported that small concentrations of a different element can tune the crystal structure of a material in the nanoparticle size regime.¹⁵ The presence of a larger element in FeNiCo alloy can also enhance the spin-orbit coupling and thus the magnetocrystalline anisotropy. Small additions of elements larger than Fe, Ni and Co may induce the stabilization of metastable phases that have uniaxial structures. On the other hand the interstitial insertion of carbon work has been already in progress by the PI and the preliminary results (presented below), are quite encouraging (see data in the Methodology Section). The target here is to synthesize tetragonal FeCo and Fe_xNi_yCo_z nanoparticles with room temperature coercivity in the ~ 0.1-0.3 T range, and M_s > 1.6 x10^-4 Am²/Kg.Challenge 2:  The L1₀ crystal structure stabilization in both FeNiCo and FeCo bimetallic nanoparticles via doping with light (carbon) and heavy (bismuth) elements.