In situphotoemission study ofNd1−xSrxMnO3epitaxial thin films

Abstract

We have performed an in situ photoemission study of Nd 1−x Sr x MnO 3 ͑NSMO͒ thin films grown on SrTiO 3 ͑001͒ substrates by laser molecular-beam epitaxy. The lattice constants of the thin films were relaxed from those of the substrates, and the transport properties were almost the same as those of bulk NSMO. From core-level photoemission studies, we found that the behavior of the chemical-potential shift was not much different from that of the bulk NSMO samples. In the valence-band spectra, finite intensity at the Fermi level was observed even in the insulating phase. The band dispersions of Nd 0.6 Sr 0.4 MnO 3 obtained by angle-resolved photoemission spectroscopy were almost the same as those of La 0.6 Sr 0.4 MnO 3 thin films. These results showed that NSMO is closely related to La 1−x Sr x MnO 3 in terms of the band structure, except for a decrease in the coherent spectral weight.Hole-doped perovskite manganese oxides R 1−x A x MnO 3 , where R is a rare earth ͑R =La,Nd,Pr͒ and A is an alkalineearth atom ͑A =Sr,Ba,Ca͒, have attracted much attention because of their remarkable physical properties such as the colossal magnetoresistance and the ordering of spin, charge, and orbitals. 1 Their electronic phase diagram is shown in Ref. 1. La 1−x Sr x MnO 3 ͑LSMO͒ has a large bandwidth W, and ferromagnetic metallic ͑FM͒ phase is realized between x Ӎ 0.2 and 0.5. 2 Charge-ordered ͑CO͒ insulating state is another phase which competes with the FM phase. Most of hole-doped manganites ͑x Ӎ 0.5͒ with a small W exhibit a so-called charge-exchange "͑CE͒-type" antiferromagnetic ordering with alternating Mn 3+ and Mn 4+ sites within the ͑001͒ plane. 3 Pr 1−x Ca x MnO 3 ͑PCMO͒, where W is the smallest, has a particularly stable CO state in a wide hole concentration range between x Ӎ 0.3 and 0.75. 4 Nd 1−s Sr x MnO 3 ͑NSMO͒ has an intermediate bandwidth W. In bulk NSMO, the FM state is realized between x Ӎ 0.25 and 0.48, and the CO state exists in a very narrow concentration range near x = 0.5. 1 Recently, Wadati et al. 5 studied the electronic structure of PCMO thin films grown on LaAlO 3 ͑LAO͒ ͑001͒ substrates by photoemission spectroscopy. The PCMO thin films were influenced by compressive strain from the LAO substrates. The photoemission results were quite different from those of PCMO bulk samples 6 in that the two characteristic behaviors observed in bulk samples, namely, the spectral weight transfer near the Fermi level ͑E F ͒ and the suppression of the chemical-potential shift with hole doping, were not observed. They considered it to be spectroscopic evidence for the suppression of incommensurate charge modulation in the PCMO thin films grown on the LAO substrates. Horiba et al. 7 also performed a similar photoemission study of LSMO thin films grown on SrTiO 3 ͑STO͒ ͑001͒ substrates. In contrast to PCMO thin films on LAO, the differences of the electronic structures between film and bulk 2 properties were not observed. In this work, we have investigated the electronic structure of NSMO thin films grown on STO ͑001͒ subs...

Decoupling the impact of bulk and surface point defects on the photoelectrochemical properties of LaFeO3 thin films

“…Thus, an electron in an occupied state experiences more attractive ionic potential due to relatively less screening offered by one less electron, leading to lowering of valence band energy and widening of the band gap. However, features such as composition and widths of the bands in our calculations are consistent with XPS, XES and XAS analyses of epitaxial thin lms grown by pulsed laser deposition, 27 and bulk crystals prepared by solid-state reactions. 28 Fig.…”

Voltage Control of Patterned Metal/Insulator Properties in Oxide/Oxyfluoride Lateral Perovskite Heterostructures via Ion Gel Gating

“…At −3 and −4 V gate biases, however, there is a clear shift and broadening of the XRD film peak, from the as‐grown pseudocubic (002) SrFeO 2.5 peak at ≈45.1° ( c ‐axis lattice parameter = 4.01 Å) toward higher angle, corresponding to a lattice contraction indicative of SrFeO 3‐δ oxidation. Corroborating this behavior in the absorption spectra is the development of a low‐energy absorption feature at ≈1.5 eV, which has been attributed to a mid‐bandgap hole‐doped state in SrFeO 3‐δ , [ 51 ] as well as an evident red‐shift in the spectral weight of absorptive intensity as previously reported via thermal treatment. [ 41 ] To quantify the oxidation, the XRD pattern obtained from −3 V gating was modeled as a bilayer of perovskite SrFeO 3‐δ overlaying brownmillerite SrFeO 2.5 .…”

Charge disproportionation inLa1−xSrxFeO3probed by diffraction and spectroscopic expe

“…However, only few studies have been reported on the electronic structure of the series. [15][16][17][18] Soft x-ray absorption and electron spectroscopies have revealed that holes created by Sr doping have a mixed Fe 3d -O 2p character for high Sr content whereas they are mainly of the O 2p character for low Sr content. 15 Combined studies with photoemission spectroscopy have confirmed this point and suggested that the hole ordering on the oxygen sites plays an essential role in realizing the charge disproportionated state.…”

“…15 Combined studies with photoemission spectroscopy have confirmed this point and suggested that the hole ordering on the oxygen sites plays an essential role in realizing the charge disproportionated state. 16 The present work was undertaken with the aim of gaining insight into the changes of the electronic and local structure of Fe atoms upon varying the La/ Sr ratio. It also focuses on the changes observed at the so-called CO transition at the critical concentrations of x =2/ 3 and x =3/ 4.…”