Confinement-Induced Giant Spin–Orbit-Coupled Magnetic Moment of Co Nanoclusters in TiO₂ Films

Abstract

High magnetization materials are in great demand for the fabrication of advanced multifunctional magnetic devices. Notwithstanding this demand, the development of new materials with these attributes has been relatively slow. In this work, we propose a new strategy to achieve high magnetic moments above room temperature. Our material engineering approach invoked the embedding of magnetic nanoclusters in an oxide matrix. By precisely controlling pulsed laser deposition parameters, Co nanoclusters are formed in a 5 at % Co–TiO2 film. The presence of these nanoclusters was confirmed using transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray absorption fine structure. The film exhibits a very high saturation magnetization of 99 emu/cm3. Detailed studies using X-ray magnetic circular dichroism confirm that Co has an enhanced magnetic moment of 3.5 μB/atom, while the Ti and O also contribute to the magnetic moments. First-principles calculations supported our hypothesis that the metallic Co nanoclusters surrounded by a TiO2 matrix can exhibit both large spin and orbital moments. Moreover, a quantum confinement effect results in a high Curie temperature for the embedded Co nanoclusters. These findings reveal that 1–2 nm nanoclusters that are quantum confined can exhibit very large magnetic moments above room temperature, representing a promising advance for the design of new high magnetization materials.

Spectroscopic Evidence of Localized Small Polarons in Low-Dimensional Ionic Liquid Lead-Free Hybrid Perovskites

“…X-ray absorption spectroscopy (XAS) is a popular characterization technique to investigate the optoelectronic properties of correlated systems. − In general, the direct observation of spectral weight transfer (SWT) has been measured in XAS spectra across diverse perovskites, which underpins the underlying theoretical foundation of the charge transfer mechanism. − Arramel et al utilized XAS to perform SWT analyses, unraveling the intimate relationship of structural transition, optical response, and electronic variation across A 2 CuCl 4 single crystals . Recently, Jun and co-workers also reported several aspects of the utilization soft X-ray scanning transmission X-ray microscopy on perovskite solar cells, which concentrated on the XAS N K-edge of 3D HOIPs such as MAPbI 3 , FAPbI 3 , and FAMAPbI 3 .…”

Defect-Rich Dopant-Free ZrO2 Nanoclusters and Their Size-Dependent Ferromagnetism

“…Recently, we showed that dopant-free, defect-rich ZrO 2 nanowire and nanobrick films exhibit strong ferromagnetic properties at room temperature. 12 Unlike the conventional dilute magnetic semiconductors (DMSs) such as Mndoped GaAs or InAs, these undoped ferromagnetic transitionmetal oxide nanostructured films have a significantly higher Curie temperature (T C ) than those of conventional DMSs with T C < 200 K. 27 For materials with promising magnetic applications at room temperature, their Curie temperature should be greater than 500 K. 28 Although some transparent oxide DMSs, such as Cr-doped In 2 O 3 films 29 and Co-doped TiO 2 film, 31 have generally high T C and could therefore serve as a viable material alternative for room-temperature spinbased electronic applications, the solubility of the dopants remains one of the biggest challenges that limit their potential application. Furthermore, the nonuniform distribution of the dopants caused by their natural tendency to form aggregates leads to inhomogeneous magnetism within the material.…”

“…For materials with promising magnetic applications at room temperature, their Curie temperature should be greater than 500 K . Although some transparent oxide DMSs, such as Cr-doped In 2 O 3 films and Co-doped TiO 2 film, have generally high T C and could therefore serve as a viable material alternative for room-temperature spin-based electronic applications, the solubility of the dopants remains one of the biggest challenges that limit their potential application. Furthermore, the nonuniform distribution of the dopants caused by their natural tendency to form aggregates leads to inhomogeneous magnetism within the material. , As defects in crystalline structures appear to play an important role in dopant-free ferromagnetic oxides, , these oxides could have the advantage of uniform magnetization.…”