Pulsed Laser Deposition of Rocksalt Magnetic Binary Oxides

Abstract

Magnetic binary oxides with the rocksalt structure constitute an important class of materials for potential applications as electronic or electrochemical devices. Moreover, they often become a theoretical playground, due to the simple electronic and crystal structures, in the quest for novel phenomena. For these possibilities to be realized, a necessary prerequisite would be to grow atomically ordered and controllably-strained binary oxides on proper substrates. Here we systematically explore the use of pulsed laser deposition technique (PLD) to grow three basic oxides that have rocksalt structure but different chemical stability in the ambient atmosphere: NiO (stable), MnO (metastable) and EuO (unstable). By tuning laser fluence FL, an epitaxial single-phase NiO thin-film growth can be achieved in a wide range of growth temperatures 10 ≤ TG ≤ 750 °C. At the lowest TG, the out-of-plane strain raises to 1.5%, which is five times higher than in NiO film grown at 750 °C. MnO thin films that had long-range order were successfully deposited on the MgO substrates after appropriate tuning of deposition parameters. The growth of MnO phase was strongly influenced by FL and the TG. EuO films with satisfactory quality were deposited by PLD after oxygen availability had been minimized. Synthesis of EuO thin films at rather low TG = 350 °C prevented thermally-driven lattice relaxation and allowed growth of strained films. Overall, PLD was a quick and reliable method to grow binary oxides with rocksalt structure in high quality that can satisfy requirements for applications and for basic research.Thin-film deposition is a technique that can be used to control strain in materials [22]. The Curie temperature TC of EuO thin film is strongly dependent on the strain and on film thickness tF [23]. Dislocations in NiO thin films locally change the magnetic ordering from antiferromagnetic to ferromagnetic [24]. Such 'ferromagnetic' dislocations originate from a local non-stoichiometry at in dislocation cores where Ni is deficient. A slight deviation from the stoichiometry also changes the conduction behavior in NiO thin films. Oxygendeficient EuO shows metallic behavior with a substantial increase of the TC to 120 K [25]. The deposition of high-quality magnetic binary oxides, and the ability to control the level of strain and density of defects in their structure, are challenging tasks in materials science and solid-state physics.Pulsed-laser deposition technique (PLD) has many advantages for growing thin films of high-quality oxides [26][27][28][29][30][31]. PLD can preserve the stoichiometry of the film composition,

Spin-phonon interaction increased by compressive strain in antiferromagnetic MnO thin films

“…All substrates were cleaned ultrasonically in acetone and methanol for 10 min in each to remove the contaminations from the top surface. After drying under a high purity nitrogen gas flow, the annealing process was carried out according to the [29]. After several attempts we realized that 1150 °C is the most proper temperature to control the surface treatment of MgO (0 0 1) substrate and 950 °C for MgO (1 1 0).…”

“…In case of MgO (1 1 0), we reduced the annealing temperature as the surface is more active (less atomic density) and higher annealing temperatures makes the treatment process out-of-control resulting in a rough surface. The more detailed explanation is available in [29].…”

“…A KrF pulsed laser (λ = 248 nm) with a repetition rate of 10 Hz was operated to ablate the ceramic pellet. During the deposition process, the substrate was heated to 650 °C, which is the optimal temperature to grow MnO films of highest quality [29]. A detailed study on the pulsed laser deposition of MnO film on MgO substrate showed that below 650 °C the deposited film contained higher oxidized phase like Mn 3 O 4 [29].…”

“…During the deposition process, the substrate was heated to 650 °C, which is the optimal temperature to grow MnO films of highest quality [29]. A detailed study on the pulsed laser deposition of MnO film on MgO substrate showed that below 650 °C the deposited film contained higher oxidized phase like Mn 3 O 4 [29]. The films grown at higher temperatures do not present high-quality surface (ω rocking curve around the (0 0 2) Bragg peak (not shown) revealed a single broad peak indicating a mosaic structure) which can affects the IR spectra in a negative way.The MnO films were grown under vacuum of 10 −6 Torr.…”

Property and cation valence engineering in entropy-stabilized oxide thin films

“…S6 and S7 [30]). The entropy-stabilized nature of J14 appears to disperse the Co 3+ enough to prevent the nucleation of Co 3 O 4 or other higher oxide phases, which commonly occurs in binary transition metal rocksalt oxide films to accommodate cation oxidation to 3+ [50][51][52]. Judging from our structural models, 400 °C likely represents a threshold tem- perature, below which Co 3+ is incorporated into the rocksalt structure and above which metastable Co 3+ converts to a more stable 2+ state at the growing surface to produce a phase similar to bulk J14.…”