Body-centered cubic (bcc) Fe is known as a typical soft magnetic material with high-saturation magnetization $\left(M_s\right)$ and low magnetocrystalline anisotropy. However, first-principles calculations demonstrate that body-centered tetragonal (bct) Fe has higher magnetocrystalline anisotropy than bcc Fe and comparable $M_s$. In this work, bct Fe nanoparticles (NPs) were successfully fabricated by a gas-phase condensation method for the first time. The bct Fe phase is confirmed by the x-ray diffraction pattern and diffraction images of transmission electron microscopy. An increased magnetocrystalline anisotropy of bct Fe, $\left(2.65\pm 0.67\right)\times 10^5\mathrm{J}/{\mathrm{m}}^3\mathrm{[}\left(21.2\pm 5.3\right)\mu \mathrm{eV}/\mathrm{atom}]$, is observed, which is around seven times higher than that of bcc Fe $4.8\times 10^4\mathrm{J}/{\mathrm{m}}^3\left(3.5\mu \mathrm{eV}/\mathrm{atom}\right)$. The bct Fe NPs sample has coercivity of $3.22\times 10^5$ A/m at 5 K and $1.04\times 10^5$ A/m at 300 K, which are much higher than that of bcc Fe NPs. In addition, the saturation magnetization at 5 K is estimated to be $\left(1.6\pm 0.4\right)\times 10^6$ A/m $\left(2.2\pm 0.5{\mu }_B/\mathrm{atom}\right)$, comparable to that of bcc Fe $1.7\times 10^6$ A/m $\left(2.2{\mu }_B/\mathrm{atom}\right)$.

• Received 15 September 2017
• Revised 11 January 2018

DOI:https://doi.org/10.1103/PhysRevMaterials.2.054415