Gas-phase synthesis and magnetism of HfO₂ nanoclusters

Abstract

Since the unexpected room-temperature ferromagnetism was found in undoped HfO₂ thin film, the origin of ferromagnetism became a debatable research hotspot The HfO₂ nanostructure materials prepared by traditional synthetic methods usually shows monoclinic phase. In this work, tetragonal phase HfO₂ nanoclusters (NCs) with uniform morphology and diameters ranging from 7 to 12 nm were prepared via plasma gas condensation cluster beam deposition technique. By annealing at 300, 600, 800 °C in air and Ar(95%) + H₂(5%) for 3 h, respectively, the HfO₂ NCs gradually transformed from tetragonal phase into monoclinic phase. The magnetic measurement results showed that as-prepared HfO₂ NCs with either tetragonal or monoclinic phase were paramagnetic, which is different from the diamagnetic behavior of bulk HfO₂ and is also not in agreement with ferromagnetism reported in some other works.