Room temperature magnetic anisotropy in Fe2P-type transition metal based alloys

We explore the crystal structure and magnetic properties of quaternary materials deriving from the hexagonal Fe2P, an iron binary known to present a particularly large magnetocrystalline anisotropy potentially interesting for permanent magnets, but with unfortunately a Curie temperature far too low for applications. Using simultaneous metal and metalloid substitutions in Fe2-zCozP1-xBx and Fe2-zCozP1-ySiy quaternaries, we found it is possible to increase the Curie temperature up to at least 640 K while maintaining a c axis uniaxial magnetocrystalline anisotropy, leading to an appreciable magnetic anisotropy at room temperature. In Fe2-zCozP1-xBx, though boron is appropriate to increase the Curie temperature, its amount is limited as it also favors the formation of secondary phases. Contrary to what could be anticipated from the phase diagrams of Fe2-zCozP or Fe2P1-ySiy ternaries, simultaneous Co for Fe and Si for P substitutions in Fe2-zCozP1-ySiy are found to significantly expand the range of stability of the Fe2P-type crystal structure. X-ray diffraction patterns on powders oriented in magnetic field indicate a c axis uniaxial magnetic anisotropy. Appropriate heat-treatments and slight metal deficiency are found suitable to limit the formation of unwanted secondary phase with 3:1 metal:metalloid ratio. As a result, nearly single-phase Fe1.95-zCozP1-ySiy materials are prepared and exhibit an appreciable magnetic anisotropy with K1 up to approximately 0.93 MJm−3 at room temperature. This study experimentally demonstrates that Fe2P-type transition metal quaternaries can present an interest not only for their first-order magnetic transition, but also for their magnetic anisotropy making them potential candidates for magnetostatic applications. [Display omitted] •A sizable magnetic anisotropy is obtained in Fe2P-quaternaries at room temperature.•Phase diagrams and structure-properties relations of Fe2P-quaternaries are explored.•Fe2-zCozP1-ySiy alloys preserve an Fe2P-type crystal structure up to y ∼0.6.•Fe2-zCozP1-ySiy alloys present high Curie temperature and uniaxial anisotropy.•Fe1.8Co0.2P1-xBx alloys are synthesized, but B content is limited to x ∼0.12