Interface and Surface Cation Stoichiometry Modified by Oxygen Vacancies in Epitaxial Manganite Films

Abstract

Perovskite manganites are viewed as one of the key building blocks of oxide spintronics devices due to their attractive physical properties. However, cation off-stoichiometry at epitaxial interfaces between manganites and other materials can lead to interfacial dead layers, severely reducing the device performance. Here, transmission electron microscopy and synchrotron-based spectroscopy are used to demonstrate that oxygen vacancies during growth serve as a critical factor for modifying the cation stoichiometry in pulsed laser deposited La 0.8 Sr 0.2 MnO 3 fi lms. Near the fi lm/substrate (SrTiO 3 ) interface, A-site cations (La/Sr) are in excess when oxygen vacancies are induced during fi lm growth, partially substituting Mn. Simultaneously, Sr cations migrate towards the fi lm surface and form a SrO rock-salt monolayer. Consequentially, a gradient of the Mn nominal valence is observed along the fi lm growth direction, leading to anomalous magnetic properties. The results narrow the selection range of useful oxygen pressures during deposition and demonstrate that accurate cation stoichiometry can only be achieved after oxygen vacancies are eliminated during growth. This fi nding suggests that the oxygen pressure serves as a tuning parameter for the interfacial dead layers and, hence, for control over device properties.

Unveiling the Outstanding Oxygen Mass Transport Properties of Mn-Rich Perovskites in Grain Boundary-Dominated La0.8Sr0.2(Mn1–xCox)0.85O3±δ Nanostructures

“…Interestingly, this indicates the presence of a B-site-deficient perovskite previously observed for low oxygen partial pressure PLD-deposited LSM layers. 38,39 …”

An Epitaxial Ferroelectric Tunnel Junction on Silicon

“…Afterwards, LSMO, which worked as an electrode to facilitate electrical measurements, was subsequently deposited at a temperature of 780 ºC under an oxygen pressure of 26 Pa, avoiding oxygen vacancies and cation non-stoichiometry during growth. [ 31 ] The BTO was grown at 650 ºC under an oxygen pressure of 7 Pa. The samples were annealed for 0.5 h at 650 ºC and then cooled to room temperature, all under an oxygen pressure of 1000 Pa. A Rigaku Smartlab high-resolution diffractometer with copper X-ray generator tube was used for XRD measurements.…”

Correlating interfacial octahedral rotations with magnetism in (LaMnO3+δ)N/(SrTiO3)N superlattices

“…In our case, the increase of the out-of-plane Mn-O-Mn bond angle with decreasing N is apparent in ( The current finding may provide a new insight to the 'dead' layer issue that are commonly found at the interface between manganite oxides and many perovskite substrates 36 , and has attracted renewed interests. In recent studies, orbital ordering, 37 polar discontinuity 38,39 , magnetic coupling to the titanate layer, 40 stoichiometry 41,42 and so on, have all been evidenced to couple to the interface magnetic property of the manganite layer, while a unified scenario is still lacking. Some recent studies on La 0.67 Sr 0.33 MnO 3 /SrTiO 3 interfaces have merged on the finding of increased amount of Mn 3 þ near the interface [43][44][45] and 3z 2 À r 2 orbital ordering irrespective of the strained state 37,45,46 .…”