Magnetic properties of Ge, Re and Cr substituted Fe5SiB2

One of the possible approaches to decrease the demand for critical elements such as rare earths is to develop new sustainable magnets. Iron-based materials are suitable for gap magnets applications since iron is the most abundant ferromagnetic element on Earth. Fe5SiB2 is a candidate as gap magnet thanks to its high Curie temperature (T-C similar to 800 K) and specific saturation magnetization (M-S similar to 140 Am(2)kg(-1)). However its anisotropy field is too low for applications (mu H-0(A) similar to 0.8 T). In order to increase the anisotropy value, we synthesized a series of Ge, Re and Cr substituted Fe5SiB2 compounds and studied their magnetic properties. They all crystallize in the Cr5B3-type tetragonal structure with the I4/mcm space group. Curie temperature (T-C = 803 K) and specific saturation magnetization (M-S = 138 Am(2)kg(-1)) are slightly decreased by elemental substitution with Re having the largest effect. Despite being reduced, T-C and M-S still maintain significant values (T-C > 750 K and M-S = 118 Am(2)kg(-1)). The room temperature anisotropy field has been measured by Singular Point Detection (SPD) and increases by about 15 % upon Re substitution, reaching 0.92 T for Fe4.75Re0.25SiB2. We have also used Nuclear Magnetic Resonance and SPD measurements to study the spin reorientation transition which takes place at 172 K and we have found that it is partially suppressed by substitution of Ge from 172 K to 140 K and completely suppressed upon Cr and Re substitution.