Structures and magnetic properties of Fe–N alloys formed by ball milling of mixture of Fe and BN

Diffusion reaction between Fe and BN and structural and magnetic properties of Fe–N alloys are investigated by ball milling of mixture of the α-Fe and hexagonal BN powders with volume ratio of 1:12.5, 1:5.4, 1:1.2 and 1:0.38 up to 72 h. It is found that Fe can react with N of the BN to form amorphous Fe–N alloy (α-Fe–N) when the grain size of the Fe decreases to 8 nm and the hexagonal BN transforms into amorphous BN; further milling, α-Fe–N can crystallize to ε-FexN. The formation of ε-FexN is related to the volume ratio of Fe to BN, when the ratio is larger than 1:0.38, no ε-FexN forms. The N content of ε-FexN increases with milling time and the volume ratio increased, resulting in decrease in saturation magnetization of ε-FexN. ε-FexN transforms from ferromagnetism to paramagnetism, when the N content exceeds 43 at%.