The main challenge of the NaNoMag project is the development of new hard magnetic materials without the presence of rare earths, focusing on the synthesis of new magnetically hard phases such as L1₀ FeCoNi and FeCo.

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.

Objective 2. Synthesis of nanocomposite magnets via “epitaxial-like” growth of L1₀ FeCo on L1₀ FePt or CoPt nanoparticles in liquid phase reactions.

This objective includes for the first time the synthesis of nanocomposite hard magnetic materials based on traditional L1₀ FePt and CoPt nanoparticles coated with L1₀ FeCo shells. The main advantage of these nanocomposite magnets, that we propose here, is that both core and shell parts of the nanostructured particles contribute simultaneously to the magnetocrystalline anisotropy and the saturation magnetization, in contrast with the heavy diamagnetic L1₀ CuAu and as a result it affects the energy product of the overall material (see state of the art section). Additionally, the Pt content will be significantly decreased in the final composites core/shell particles. We estimate the Pt content to decrease from 50 at. % in the L1₀ FePt alloys, to less than 25 at. % in the L1₀ nanocomposite core/shell particles. To achieve this we propose the synthesis of L1₀ FePt at the smallest nano-size possible, (<20 nm), maximizing the surface area for the epitaxial growth of L1₀ FeCo shells. The L1₀ FePt nanoparticles that will used as seeds will have >1 T, room temperature coercivity, leading to nanocomposite core/shell particles with Hc in the range of 0.4-0.8 T. The PI has already experience on the synthesis of L1₀ FePt and CoPt nanoparticles directly in liquid phase with 15.2 kOe room temperature coercive field in the 20 nm diameter size regime.¹⁴

Objective 3. Synthesis of a prototype permanent magnet.

This objective includes the fabrication of a 1 gr prototype permanent magnet. The experienced research with the appropriate complementary training on magnetism and especially nanomagnetism and technology concerning magnet fabrication will focus on the preparation of a prototype 1 gr magnet from the nanoparticle materials that will be synthesized during the project. The nanoparticle powders will be aligned and compacted at room temperature to form a “green compact”. This compact will be consolidated at low temperatures (preferably below 700 ^oC) to form a magnet with a density close to that of bulk samples. The target here is a prototype magnet with an energy product higher than 100 kJ/m³ and Curie temperature greater than 300 ^oC.