Observation of room temperature ferromagnetic behavior in cluster-free, Co doped HfO2 films

Abstract

Extensive structural and magnetic analyses of Hf 1−x Co x O 2 thin films grown by molecular beam epitaxy are reported. Nearly cobalt cluster-free film with x = 0.04-0.1 was obtained via 100°C growth, and Co ions are inferred to be located at interstitial site. Ferromagnetic behavior was observed up to 300 K in both magnetization curves and temperature dependence of the moment. Via post-oxygen-annealing studies, a qualitative correlation between saturation magnetization and oxygen vacancy concentration is established, consistent with the impurity-band exchange model, and that the occurrence of ferromagnetic insulator behavior in the Co doped HfO 2 is more probable than Co doped ZnO, TiO 2 , and SnO 2 systems for doping concentrations under cation percolation threshold.

Effects of single O vacancy on the magnetism and electronic structure of Ti doped CoO: A first principle study

“…In addition, the transitional metal-doped oxides including TiO 2 [6,7], In 2 O 3 [8,9], SnO 2 [10][11][12], CuO [13,14], HfO 2 [15][16][17][18] and ZnO [19,20] are also investigated. Till now, many problems still exist in DMSs, such as the low Curie temperature, weak ferromagnetism, etc.…”

Effect of native defects and Co doping on ferromagnetism in HfO2: First‐principles calculations

“…Another approach to achieve the ferromagnetism is doping transition metal atoms in HfO 2 . Room temperature ferromagnetism has been observed in cobalt‐doped HfO 2 10–12. However, all the ferromagnetism is due to the cobalt clusters or other defects in these materials, i.e., it is extrinsic.…”

Room temperature ferromagnetism in Ni-doped HfO2 thin films

“…The dilute ferromagnetic oxides have emerged as a possible candidate for spintronic applications because of their wide band gap and high Curie temperature (T C ) well above room temperature [1,2]. There are many reports on room temperature ferromagnetism [3][4][5][6][7] in transition element doped oxides that may be partially compensated. Ferromagnetism is observed in these oxides at 3d dopant concentration that is far below percolation threshold (x p ) associated with nearestneighbour cation coupling.…”

“…The average moments sometimes exceed by far the spin-only moments [8]. Hafnium dioxide (HfO 2 ) is one of such potential high-k dielectrics and wide band-gap oxides on which effects of doping of transition-metal elements such as Ni and Co are reported [3][4][5]9]. However, transition element segregation at the surface or clustering of the dopant elements during high temperature growth by usual 4 Author to whom any correspondence should be addressed.…”

“…techniques such as molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) leads to controversial results [4,5] of the origin of magnetism. The reason for large magnetic moment and large anisotropy in most of these systems is still not understood clearly and the cause of magnetism in these oxides is still debated [8][9][10][11][12][13].…”