The Effect of A-Site Substitution of Ce and La on the Magnetic and Electronic Properties of Sr(Ti_0.6Fe_0.4)O_3−δ Films

Abstract

The structure and magnetic properties of epitaxial (Ce(x)Sr(1-x))(Ti(0.6)Fe(0.4))O(3-δ) (x = 0, 0.1, 0.2 and 0.3) and (La(x)Sr(1-x))(Ti(0.6)Fe(0.4))O(3-δ) (x = 0, 0.1, 0.2, 0.3 and 0.4) perovskite-structure thin films deposited by pulsed laser deposition on (LaAlO(3))(0.3)(Sr(2)AlTaO(6))(0.7) (LSAT) substrates are reported. Both La and Ce ions showed a dominant 3+ valence state and acted as donors on the Sr(2+) site (A site) in the perovskite lattice. The optical band gap widened, and the Fermi level moved toward the vacuum level with increased Ce or La content; meanwhile the Ti and particularly the Fe ions were driven to a lower valence state, resulting in a higher Fe(2+) concentration. The materials were magnetic at room temperature with up to 0.8 μ(B)/Fe and a magnetoelastic out-of-plane anisotropy. Ce and La lowered the coercivity while raising both the Faraday rotation at 1550 nm and the optical absorption at near-infrared wavelengths.

Magneto-Optical Thin Films for On-Chip Monolithic Integration of Non-Reciprocal Photonic Devices

“…On the other hand, the optical transparency followed a reverse trend compared to the Faraday rotation, indicating a trade-off between Faraday rotation and optical transparency. This trade-off can be mitigated by choosing proper dopants and concentrations; therefore, a higher magneto-optical FoM can be achieved [99,100]. Figure 5 shows the optical transparency of Ga-doped STF films and a strip-loaded waveguide fabricated on an LSAT substrate.…”

“…Also shown are the Faraday rotations as a function of dopant concentration for ( c ) Ce substituted STF and ( d ) Ga substituted STF films [99,100] on LSAT. (Reprinted with permission from [99,100]. Copyright 2011 AIP Publishing LLC).…”

XMCD study of magnetism and valence state in iron-substituted strontium titanate

“…In bulk STF, the Fe ions typically exist with an Fe 3+ or Fe 4+ oxidation state [16,17]. However, thin film growth such as by pulsed laser deposition (PLD) under low oxygen pressures can lead to the presence of Fe 2+ [18][19][20][21][22] as observed by surface sensitive techniques, due to the kinetically-limited growth process which results in a high concentration of oxygen vacancies that are compensated by changes to the cation valence state [18]. Although x-ray photoelectron spectroscopy (XPS) studies of Fe-substituted STO have been conducted [15,20,21], there is no study of STF using both x-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) which can provide a detailed microscopic mechanism for the emergence of magnetism with bulk sensitivity.…”

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

“…STO is highly transparent near λ = 1.55 μm in thin film and waveguide forms [3,4]. 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].…”