Structural rearrangement and surface magnetism on oxide surfaces: a 
temperature-dependent low-energy electron diffraction-electron energy loss 
spectroscopy study of Cr2O3(111)/Cr(110)

Bender, M.; Ehrlich, D.; Yakovkin, I. N.; Rohr, F.; Baumer, M.; Kuhlenbeck, H.; Freund, Hans-Joachim; Staemmler, V.

doi:10.1088/0953-8984/7/27/014

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Structural rearrangement and surface magnetism on oxide surfaces: a temperature-dependent low-energy electron diffraction-electron energy loss spectroscopy study of Cr₂O₃(111)/Cr(110)

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Bender, M., Ehrlich, D., Yakovkin, I. N., Rohr, F., Baumer, M., Kuhlenbeck, H., et al. (1995). Structural rearrangement and surface magnetism on oxide surfaces: a temperature-dependent low-energy electron diffraction-electron energy loss spectroscopy study of Cr₂O₃(111)/Cr(110). Journal of Physics: Condensed Matter, 7(27), 5289-5301. doi:10.1088/0953-8984/7/27/014.

Cite as: https://hdl.handle.net/21.11116/0000-000E-44D5-5

Abstract

Structural rearrangements of the (111) surface in the system Cr₂O₃(111)/Cr(110) as a function of temperature were investigated by means of low-energy electron diffraction (LEED) and electron energy loss spectroscopy (EELS). At room temperature, one observes a simple (1x1) LEED pattern of the clean (111) surface. If the temperature was lowered to 150 K a (√3x√3)R30˚ superstructure was observed. The structure reached its maximum intensity at about 150 K substrate temperature. Below 150 K the simple (1x1) LEED pattern of the (111) surface was recovered at 90-100 K. Parallel to this, a considerable change in the electron energy loss spectra with varying temperature was observed. With the help of quantum-chemical cluster calculations the low-energy excitations in the range between 0.8 and 2.5 eV were assigned to local d-d excitations of Cr³⁺ ions at the Cr₂O₃(111) surface. Some of these peaks were quenched upon adsorption of gases such as CO, NO or CO₂. We propose a model of two successive phase transitions the first of which is a disorder-to-order transition above 150 K whereas the second is an order-to-order transition below 150 K. The transitions may be driven by antiferromagnetic coupling of the surface chromium ions to those in the second layer.