September 1, 2015 at 6:15 pm

CMSS Colloquium | Investigating Spin-Polarized Surface States of Magnetic Nitride Systems Using Scanning Tunneling Microscopy and Spectroscopy, Sept. 24

Arthur Smith

Arthur Smith

The Condensed Matter & Surface Sciences Colloquium Series presents Arthur Smith of Ohio University on “Investigating Spin-Polarized Surface States of Magnetic Nitride Systems Using Scanning Tunneling Microscopy and Spectroscopy.” on Thursday, Sept. 24, at 4:10 p.m. in Walter 245.

Abstract: Current investigations in my group continue to explore the properties of magnetic nitride systems using a combination of molecular beam epitaxy and scanning tunneling microscopy & spectroscopy. As examples, we are currently investigating both manganese nitride and chromium nitride. Manganese nitride exhibits a complex antiferromagnetic behavior at its surfaces. Our early work on CrN (Constantin 2004) demonstrated a metal/semiconductor electronic phase transition near 285 K. Additional work by other authors, both theoretical and experimental, has further heightened the interest in this material. In a recent set of new experiments, we have investigated both the magnetic as well as structural transition for CrN thin films. We are furthermore using scanning tunneling spectroscopy to investigate the electronic & magnetic properties of nano-sized iron islands on CrN at low (4.2K) temperature, and we are also looking into the exchange coupling behavior of Fe/CrN bi-layer films.

In another project, we are investigating the properties of a rare and unusual manganese Ö3 x Ö3-R30º reconstruction on gallium nitride using tunneling spectroscopy and dI/dV conductance imaging. We are finding, in agreement with first principles theoretical calculations, that this surface is magnetic.  Conductance dI/dV images reveal evident magnetic domains, and from the dI/dV asymmetry we calculate the effective spin polarization. Normalized conductance spectra furthermore reveal both filled and empty surface state peaks which may be compared directly to densities of states for this surface based on first principles calculations.  Application of small magnetic fields during the spectroscopy measurements results in changes to the spectra, the causes of which are being postulated. One possibility is a spin-orbit effect, which appears at first however to have difficulty explaining the magnitude of the changes seen.

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