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.