Proposal of New Co-Addition Method for α”-Fe₁₆(N, C)₂ Particles by Gas–Solid Reactions

Metastable
$\alpha '$
-Fe-N (12 at% N) and
$\alpha '$
-Fe-C (12 at% C) are unique materials with a magnetocrystalline constant
$K_{1}$
of +
$5\times10$
⁶
and
$- 7\times10$
⁶
erg/cm
³
, respectively, according to measurements based on thin films. Therefore, co-addition
$\alpha ''$
-Fe
$_{16}X_{2}$
(
$X $
= N, C) particles are attractive as potential new soft magnetic materials because their magnetocrystalline constant can be varied by manipulating their N and C concentrations. However, introducing C interstitially into
$\alpha $
-Fe particles by the carbonization process using a C-containing gas such as CO gas is difficult because the equilibrium phase Fe
₃
C is easily generated. Therefore, we investigated various reaction routes of nitridation and carbonization, along with various C-containing gases, to prepare co-addition
$\alpha ''$
-Fe
₁₆
(N, C)
₂
particles. We obtained
$\alpha ''$
-Fe
₁₆
(N, C)
₂
particles using a route in which
$\alpha $
-Fe was obtained by reduction of Fe
₃
O
₄
particles, followed by nitridation to
$\alpha ''$
-Fe
₁₆
N
₂
and subsequent carbonization to
$\alpha ''$
-Fe
₁₆
(N, C)
₂
. The amount of C particles after carbonization was measured to be 0.8 wt% (3.6 at%). This gas–solid reaction process based on the concept of using
$\alpha ''$
-Fe
₁₆
N
₂
as a material with an expanded
$\alpha $
-Fe lattice is a useful method for the co-addition of interstitial N and C.