Surface Valence States of Mn Ions and Magnetic Properties of La<sub>0.67</sub>Sr<sub>0.33</sub>MnO<sub>3</sub> Films

Abstract

La 0.67 Sr 0.33 MnO 3 (LSMO) films were prepared on SrTiO 3 single-crystal substrates by the pulsed laser deposition method. X-ray photoelectron spectra (XPS) were measured for the LSMO films as-prepared, annealed in oxygen and in vacuum, respectively. Multiple peaks fitting for Mn 2p 3/2 XPS spectra shows that Mn 2+ appears and the ratio of Mn 3+ /Mn 4+ increases on the surface of LSMO film annealed in vacuum comparing with the as-prepared film, though the saturation magnetization (M s ) changes little. Mn 6+ and Mn 7+ can be detected while Mn 4+ decreases much on the surface of LSMO film annealed in oxygen. The change of Mn 3+ /Mn 4+ results in the obviously reduce of M s . O1s spectra show the gradual changes of Mn-O, Sr-O and La-O. Analysis indicates that Mn 2+ forms at the surface defects of LSMO films. Annealing in vacuum hardly affects the magnetic property of LSMO films. But annealing in oxygen greatly changes the valence states of Mn, which weakens the magnetic property of LSMO films.

Anomalous Temperature-Induced Particle Size Reduction in Manganese Oxide Nanoparticles

“…These indicate that the low valence state of Mn is more accessible at low temperatures, while a higher oxidation state of Mn dominates at 150 °C. Two plausible chemical forms of Mn 3 O 4 as bivalence of Mn are MnO 2 -2MnO ,,− with an area ratio of Mn 2+ /Mn 4+ at ∼1.33 or MnO-Mn 2 O 3 with the ratio of Mn 2+ /Mn 3+ at 1.8–2 . According to this study, we propose that the former cases share similarity to MO90 and MO150, with the mixed-valence ratios of 1.13 and 1.18, respectively.…”

“…45,52,60, and 65°attributed to the Miller indices of (101), (112), (103), (211), (004), (220), (105), (224), and (400), respectively, confirming the hausmannite phase of the Mn 3 O 4 spinel structure 3. The formation of Mn 3 O 4 was also confirmed by Raman spectra, as shown in FigureS1.…”

“…The Mn 2p peak shows multiple splitting into Mn 2p 1/2 and Mn 2p 3/2 , with a splitting peak distance at about 11.5 eV, in accordance with previous studies. ,,,, In order to elucidate Mn species with different oxidation states, further deconvolution of the Mn 2p suggests four different species of manganese cations spanning in the ranges of 638.84–640.91, 641.35–642.24, 643.69–643.69, and 645.94–645.87 eV. These values correspond to the different oxidation states of Mn 2+ , , Mn 3+ , , Mn 4+ , , and Mn 7+ , , respectively. We attributed the extracted binding energies to compounds such as MnO or Mn(OH) 2 , , Mn 2 O 3 or Mn(OOH), , MnO 2 , and MnO 4 – , respectively.…”

“…These values correspond to the different oxidation states of Mn 2+ , 3,58 Mn 3+ , 59,60 Mn 4+ , 3,59 and Mn 7+ , 60,61 respectively. We attributed the extracted binding energies to compounds such as MnO or Mn(OH) 2 , 3,58 Mn 2 O 3 or Mn(OOH), 58,60 MnO 2 , and MnO 4 − , respectively. In general, the manganese species in MO90 is dominated by Mn 3+ and Mn 2+ , while MO150 has the lowest amount of Mn 3+ , with a corresponding increase in proportion of Mn 4+ and Mn 7+ .…”

“…These values correspond to the different oxidation states of Mn 2+ , , Mn 3+ , , Mn 4+ , , and Mn 7+ , , respectively. We attributed the extracted binding energies to compounds such as MnO or Mn­(OH) 2 , , Mn 2 O 3 or Mn­(OOH), , MnO 2 , and MnO 4 – , respectively.…”