Atomic Structure and Magnetic Properties of HfCo $_{7}$ Alloy

Co rich Hf-Co alloys demonstrate promising properties as potential permanent magnet systems. However their structure has not been well established by experiment. We performed a search for low-energy structures of the HfCo₇ system with recently developed adaptive genetic algorithm. Among the low-energy structures with 16 and 32 atoms per unit cell, we found structural motifs similar to the permanent magnet SmCo₅. For the unit cell size larger than 40 atoms, we found a phase separation into pure hcp Co and Hf₂Co₇ in agreement with the experiment. Calculated magnetization and temperature of magnetic phase transition are similar to those for hcp Co. Overall considered HfCo₇ system represents a mix of in- and out-of-plane magnetic anisotropies systems with possible site dependence of magnetic anisotropy.