Towards measurement of magnetic properties of single atomic columns

Datum

11.03.2015

Zeit

14:00 - 15:00

Sprecher

Dr. Jan Rusz

Zugehörigkeit

Department of Physics and Astronomy, Uppsala University, Sweden

Sprache

en

Hauptthema

Materialien

Andere Themen

Materialien, Physik

Host

Svea Fleischer

Beschreibung

Achieving quantitative measurements of bulk magnetic properties with atomic lateral resolution is one of the great promises of modern aberration-corrected scanning transmission electron microscopes. The principle that allows measuring magnetism in an electron microscope is based on electron magnetic circular dichroism (EMCD; [1]), an electron analogue of the established x-ray magnetic circular dichroism. It is expected that with electron vortex beams [2] it should be possible to measure EMCD at an atomic resolution [3], although forming atomic sized vortices remains a challenge. The most promising approaches are based on magnetized needles [4,5] or utilizing additional lens for magnifying the beam split by a fork aperture [6,7], selecting the desired vortex with a slit and demagnifying it back [8]. An alternative approach, which does not require specialized apertures and utilizes the whole electron beam intensity, is based on tuning the k-space phase distribution of the beam to the symmetry of underlying crystal [9]. For example, for cubic or tetragonal crystals one could set the four-fold astigmatism to a nonzero value (few tens of micrometers), while keeping the other aberrations as low as possible. Such approach can be implemented into any probe-corrected STEM, which offers the flexibility to independently tune individual aberrations to desired nonzero values. We will overview the theoretical principles behind atomic resolution magnetic measurements and present measurements with atomic-sized aberrated beams on an antiferromagnetic compound LaMnAsO [10]. [1] P. Schattschneider et al., Nature 441, 486 (2006). [2] M. Uchida and A. Tonomura, Nature 464, 737 (2010). [3] J. Rusz, S. Bhowmick, Phys. Rev. Lett. 111, 105504 (2013). [4] A. M. Blackburn, J. C. Loudon, Ultramicroscopy 136, 127-143 (2013). [5] A. Beche et al., Nat. Phys. 10, 26 (2014). [6] B. McMorran et al., Science 331, 192 (2011). [7] J. Verbeeck, H. Tian, and P. Schattschneider, Nature 467, 301 (2010). [8] O. L. Krivanek et al., Microscopy and Microanalysis 20, 832 (2014). [9] J. Rusz, J. C. Idrobo, S. Bhowmick, Phys. Rev. Lett. 113, 145501 (2014). [10] J. C. Idrobo et al., submitted.

Links

• Seminars at the IFW

Letztmalig verändert: 11.03.2015, 08:40:04