Magnetoelastic effects in SrTi1−xMxO3(M = Fe, Co, or Cr) epitaxial thin films

Abstract

SrTi 1−x M x O 3 films in which M = Fe, Co, or Cr and x = 0.04-0.5 have been grown epitaxially on CeO 2-buffered Si, SrTiO 3 , and LaAlO 3 substrates. Films grown in vacuum containing Fe or Co typically showed a strong uniaxial magnetic anisotropy in the out-of-plane direction, a saturation moment on the order of 0.5μ B /Fe or Co, and a magnetization that persists to temperatures of order 1000 K. In contrast, films containing Cr showed no evidence of a spontaneous magnetic moment. The films are typically in a high in-plane compressive strain state due to epitaxial growth. The results are discussed in terms of the magnetoelastic effects from specific ionic valence states, and the magnetization versus temperature curves are fitted to a model for magnetoelastic spin ordering.

Magnetism and Faraday Rotation in Oxygen-Deficient Polycrystalline and Single-Crystal Iron-Substituted Strontium Titanate

“…Iron-substituted strontium titanate or SrTi 1−x Fe x O 3−δ (STF) (here δ represents the oxygen deficiency with respect to a stoichiometric perovskite SrTi 1−x Fe x O 3 , i.e., one in which the Fe is present as Fe 4þ ) has been extensively characterized as a mixed electronic-ionic conductor [11][12][13][14][15] and for its magnetic, magneto-optical, ferroelectric, and catalytic properties [16][17][18][19]. Characterization of STF has included determining its oxygen content via thermogravimetric analysis and coulometric titration [20,21], and measurements of ionic and electronic conductivity and impedance [12,13,15,[22][23][24].…”

“…Characterization of STF has included determining its oxygen content via thermogravimetric analysis and coulometric titration [20,21], and measurements of ionic and electronic conductivity and impedance [12,13,15,[22][23][24]. The magnetic properties are believed to be related to oxygen vacancies [16,20,25], although the origin of the magnetism is not fully understood. We have previously found that epitaxial STF and SrðTi 1−x Co x ÞO 3−δ (STCo) films on SrTiO 3 (STO), LaAlO 3 , and CeO 2 =yttria-stabilized-zirconia-(YSZ) buffered (001) Si substrates grown in vacuum with x ¼ 0.1 to 0.5, i.e., nondilute systems, exhibited room-temperature magnetism and anisotropy with an out-of-plane magnetic easy axis that was attributed to magnetoelastic effects [16,17,[26][27][28].…”

“…The magnetic properties are believed to be related to oxygen vacancies [16,20,25], although the origin of the magnetism is not fully understood. We have previously found that epitaxial STF and SrðTi 1−x Co x ÞO 3−δ (STCo) films on SrTiO 3 (STO), LaAlO 3 , and CeO 2 =yttria-stabilized-zirconia-(YSZ) buffered (001) Si substrates grown in vacuum with x ¼ 0.1 to 0.5, i.e., nondilute systems, exhibited room-temperature magnetism and anisotropy with an out-of-plane magnetic easy axis that was attributed to magnetoelastic effects [16,17,[26][27][28]. However, films deposited in oxygen had no significant room-temperature magnetism.…”

“…However, films deposited in oxygen had no significant room-temperature magnetism. The magnetic moment of vacuum-deposited epitaxial STF films persisted to a temperature of >1000°C and the magnetization decreased slowly as a function of temperature [16,29,30]. Depending on the thickness and deposition conditions, STF could be grown as a singlecrystal film on STO, or as a double-epitaxial film consisting of an (001)-oriented STF film with (011)-oriented crystals growing within it, both orientations being epitaxial with the substrate [31].…”

Oxygen partial pressure dependence of magnetic, optical and magneto-optical properties of epitaxial cobalt-substituted SrTiO_3 films

“…Transition metal substituted STO films, such as Sr(Ti,Co)O 3-δ [3], (La,Sr)(Ti,Co)O 3-δ [5][6][7], and Sr(Ti,Fe)O 3-δ (STF) [8][9][10][11], exhibit room temperature magnetic and magneto-optical (MO) properties which depend on substrate, substituent type and concentration, buffer layer and film growth conditions. Faraday rotation of substituted STO films make these films attractive for integrated non-reciprocal photonic device applications [12,13] such as isolators and circulators as well as for fundamental investigations of the spectral origins of MO properties and superexchange effects [9,[14][15][16]. Substituted STO films can be grown both as polycrystalline films on Si or as single crystals on perovskite substrates, but on CeO 2 /yttriastabilized zirconia buffered Si, STF films grew with two different epitaxial orientations, forming so-called double-epitaxial growth in which the (100)-oriented film contained (110) crystals which formed to relieve strain [17].…”