Persistent optically induced magnetism in oxygen-deficient strontium titanate

Abstract

Strontium titanate (SrTiO3) is a foundational material in the emerging field of complex oxide electronics. Although its bulk electronic and optical properties are rich and have been studied for decades, SrTiO3 has recently become a renewed focus of materials research catalysed in part by the discovery of superconductivity and magnetism at interfaces between SrTiO3 and other non-magnetic oxides. Here we illustrate a new aspect to the phenomenology of magnetism in SrTiO3 by reporting the observation of an optically induced and persistent magnetization in slightly oxygen-deficient bulk SrTiO3-δ crystals using magnetic circular dichroism (MCD) spectroscopy and SQUID magnetometry. This zero-field magnetization appears below ~18 K, persists for hours below 10 K, and is tunable by means of the polarization and wavelength of sub-bandgap (400-500 nm) light. These effects occur only in crystals containing oxygen vacancies, revealing a detailed interplay between magnetism, lattice defects, and light in an archetypal complex oxide material.

Coexistence of trapped and free excess electrons inSrTiO3

“…It exhibits many attractive properties such as superconductivity 1 , ferromagnetism 2,3 , high thermoelectric coefficients 4 , blue and green light emission 5 , and can accomodate a two dimensional electron gas 6,7 . All these phenomena arise when a small number of electrons are introduced into the lattice.…”

Universality of electron mobility in LaAlO3/SrTiO3 and bulk SrTiO3

“…25,29 Let us first dwell on the interpretation of the electron mobility in nominally insulating bulk STO. It is well established that bulk STO samples usually are strongly compensated, 25,27,42 i.e., have nearly equal donor and acceptor concentrations. In bulk STO, the possible background donors include oxygen vacancies, while common acceptors include strontium vacancies, aluminium, or iron.…”

“…In bulk STO, the possible background donors include oxygen vacancies, while common acceptors include strontium vacancies, aluminium, or iron. [42][43][44] Due to a transition of electrons from donors to acceptors, the total concentration of charged background impurities can be as large as N $ 5 Â 10 18 cm -3 . 42 This means that in both bulk STO and LAO/STO-based interfaces with n 3D ( N (or n s ( 1:5 Â 10 13 cm -3 ), the electron mobility is limited by electrons scattering on background charged impurities.…”

“…[42][43][44] Due to a transition of electrons from donors to acceptors, the total concentration of charged background impurities can be as large as N $ 5 Â 10 18 cm -3 . 42 This means that in both bulk STO and LAO/STO-based interfaces with n 3D ( N (or n s ( 1:5 Â 10 13 cm -3 ), the electron mobility is limited by electrons scattering on background charged impurities. For bulk STO having n 3D ) N (or n s ) 1:5 Â 10 13 cm -3 ), the lowtemperature electron mobility is instead limited by scattering on intentionally added ionized donors.…”

Kinetics of Vacancy Doping in SrTiO3 Studied by in situ Electrical Resistivity

“…Strontium titanate (SrTiO 3 ) is one of the most studied cubic perovskites due to the fascinating physical properties [1][2][3][4] . This compound exhibits structural cubic to tetragonal transition at 105 K with a ferroelectric order simultaneous to antiferrodistorsive transition order 5 .…”