Quasi‐Two‐Dimensional Ferromagnetic SrRuO₃ Grown by Pulsed Laser Deposition with Layer‐by‐Layer Growth Fashion

Abstract

expansion increases the bandwidth and reduces the density of states (DOS) of the Fermi level, however, the strong orbital hybridization between Ru 4d and O 2p of SRO will enhance the DOS, resulting in ferromagnetic interaction and metallicity, and the Curie temperature (T c ) of bulk SRO as high as 160 K. [16,17] SRO also has good electrical conductivity, thermal property, and chemical inertia, and has a high lattice matching degree on a variety of commonly used substrates. [18,19] Recent research on SRO heterostructures and superlattices with ultra-thin SRO layer further show remarkable phenomena. Typical examples include the ferroelectric tunable topological Hall effect (THE), [20][21][22][23][24] skyrmion in BaTiO 3 /SrRuO 3 , [9] and spin chirality fluctuation in 2D SRO ferromagnets with perpendicular magnetic anisotropy. [25] Besides, SRO is also used extensively in the study of anomalous Hall effect (AHE). [8,9,26,27] In SRO, both the AHE and THE of the SRO/STO heterostructure show a strong SRO thickness (t SRO ) dependence. If the thickness is not accurate or uniform, areas with different thicknesses will be superimposed, resulting in an artificial THE signal. [28] Therefore, a layer-by-layer growth mode is desired to precisely regulate the thickness at the unit cell (u.c.) level.However, quite different from many perovskite oxides such as La 2/3 Sr 1/3 MnO 3 , LaCoO 3 , and SrTiO 3 , where a layerby-layer growth mode can persist for even 100 unit cells, the SRO usually quickly transits from layer-by-layer mode into step-flow mode. According to previous studies, when SRO thin film is grown on a TiO 2 -terminated (001) STO substrate, the terminated atomic layer changes from the B-site to the A-site in the first period, [29,30] resulting in the transition from 2D layerby-layer mode to step-flow mode. In step-flow growth mode, the RHEED intensity does not oscillate and remains stable, making the thickness of the films impossible to be intuitively monitored by RHEED. Therefore, it is difficult to accurately control the thickness of superlattices and multilayer films.In this paper, we report the exploration of layer-by-layer growth of SRO. The epitaxial SRO thin films and (SRO n /STO 5 ) 10 superlattices were grown on TiO 2 -terminated (001) STO substrates. The single TiO 2 -terminated (001) STO substrates were obtained through standard buffered oxide etch (BOE) One of the keys to the construction of metal oxide heterostructures is the short characteristic length scale, which requires controlled growth and interface engineering on an atomic level. At present, the growth mode of SrRuO 3 (SRO) thin films grown on TiO 2 -terminated (001) SrTiO 3 (STO) substrates usually transitions from 2D layer-by-layer to step-flow at the first few growth periods, which is not conducive to the construction of superlattices or multilayer films. In this paper, persistent layer-by-layer growth of SRO thin films is demonstrated by regulating the growth conditions. As a result, the thickness can be precisely controlled down to a sing...

Correlated Quantum Phenomena of Spin–Orbit Coupled Perovskite Oxide Heterostructures: Cases of SrRuO3 and SrIrO3 Based Artificial Superlattices

“…Second, a sufficiently oxygen-rich environment of 100 mTorr is required to synthesize stoichiometric SrRuO 3 and SrIrO 3 layers. [49,52] Third, since high laser fluence can induce unintended cation vacancies and change the growth modes, [53,54] a laser fluence of around 1.2 J cm -2 is typically used for the growth of SrRuO 3 (and SrIrO 3 ) layers. Finally, when constructing a superlattice, we should consider the deposition conditions of the partner layer, ensuring that they do not compromise the functionality of SrRuO 3 (or SrIrO 3 ).…”

“…Atomically designed SrRuO 3 superlattices provide further extended controllability of the correlated functionalities, depending on the type of partner oxide layer and substrate, chemical stoichiometry, individual layer thickness, repetition number, and stacking order of the supercell structure. [41,54,55,70, 4d SrRuO [164] ner compounds. [41,54,55,70, Herein, several emergent functionalities of SrRuO 3 based superlattices and their modulations are reviewed in the following Sections.…”

“…[41,54,55,70, 4d SrRuO [164] ner compounds. [41,54,55,70, Herein, several emergent functionalities of SrRuO 3 based superlattices and their modulations are reviewed in the following Sections.…”

“…Figure 9fi further show the dimensionality-induced electronic phase transition of the SrRuO 3 /SrTiO 3 superlattices with strongly coupled magnetic phase transitions. [54,98,100] Numerous experiments by different research groups consistently demonstrated the presence of electromagnetic phase transition across the dimensional crossover in the SrRuO 3 layers. On the other hand, typical residual resistance ratios of SrRuO 3 based superlattices range from 0.1 to 8 for SrRuO 3 /SrTiO 3 superlattice and around 1 for SrRuO 3 /BaTiO 3 superlattice and SrRuO 3 /LaAlO 3 superlattice.…”

“…h) Summary of the temperature-dependent resistivity of SrRuO 3 monolayer within SrRuO 3 /SrTiO 3 superlattices. [54,86,92,99,105,107,109] i) SrTiO 3 thickness-dependent resistivity of monolayer SrRuO 3 superlattice at 45 K and 300 K. The colors in the figure correspond to the labeling of Figure 10h. j) Temperature-dependent transport of monolayer SrRuO 3 superlattice with 10 unit cell layers of BaTiO 3 , red dashed line in the inset is fitting curve using parallel resister formula.…”