Assembly of uniaxially aligned rare-earth-free nanomagnets

We report HfCo ₇ nanoparticles with appreciable permanent-magnet properties (magnetocrystalline anisotropy K ₁ ≈ 10 Mergs/cm ³, coercivity H _c ≈ 4.4 kOe, and magnetic polarization J _s ≈ 10.9 kG at 300 K) deposited by a single-step cluster-deposition method. The direct crystalline-ordering of nanoparticles during the gas-aggregation process, without the requirement of a high-temperature thermal annealing, provides an unique opportunity to align their easy axes uniaxially by applying a magnetic field of about 5 kOe prior to deposition, and subsequently to fabricate exchange-coupled nanocomposites having J _s as high as 16.6 kG by co-depositing soft magnetic Fe-Co. This study suggests HfCo ₇ as a promising rare-earth-free permanent-magnet alloy, which is important for mitigating the critical-materials aspects of rare-earth elements.