Invited Paper AC+AS+MI+SA+SS-MoM5
Magnetic Circular Dichroism Measured with Transmission Electron Microscope

Monday, November 10, 2014, 9:40 am, Room 301

X-ray magnetic circular dichroism (XMCD; [1]) is an established experimental probe of atom-specific magnetic properties of lanthanides and actinides. In XMCD, a photon of well-defined energy and polarization is absorbed by an atom in the sample with a probability that is proportional to the number available unoccupied states with an energy that allows fulfilling the energy conservation and selection rules. An essential element of XMCD are so called sum rules [2,3], which relate the XMCD spectra to the spin and orbital angular momenta, respectively.

Recently, a new experimental method has been developed that is closely related to XMCD. It was named electron magnetic circular (or chiral) dichroism (EMCD) and it is measured with a transmission electron microscope (TEM) instead of a synchrotron beam-line. We will review the short history of this method starting from its proposal in 2003 [4], first experimental proof-of-the-concept in 2006 [5], formulation of the theory [6] and sum rules [7,8] in 2007 to the present state-of-the-art and early applications, for example [9-12]. Yet, despite intense efforts, EMCD is still in its development phase, particularly from the point of view of quantitative studies. On the other hand, qualitative EMCD experiments have reached resolutions below 2nm [13].

The primary advantages of the EMCD, when compared to XMCD, are costs, availability and lateral resolution. Even a state-of-the-art TEM is a device considerably cheaper than a synchrotron beam-line and as such it can be available locally to a research group. TEM is also a very versatile instrument that combines diffraction experiments, elemental analysis, local electronic structure studies via electron energy loss spectroscopy [14] and now also magnetism via EMCD.

[1] J. L. Erskine, E. A. Stern, Phys. Rev. B 12, 5016 (1975).

[2] B. T. Thole et al., Phys. Rev. Lett. 68, 1943 (1992).

[3] P. Carra et al., Phys. Rev. Lett. 70, 694 (1993).

[4] C. Hebert, P. Schattschneider, Ultramicroscopy 96, 463 (2003).

[5] P. Schattschneider et al., Nature 441, 486 (2006).

[6] J. Rusz, S. Rubino, and P. Schattschneider, Phys. Rev. B 75, 214425 (2007).

[7] J. Rusz et al., Phys. Rev. B 76, 060408(R) (2007).

[8] L. Calmels et al., Phys. Rev. B 76, 060409(R) (2007).

[9] S. Muto et al., Nature Comm. 5, 3138 (2013).

[10] Z. H. Zhang et al., Nature Nanotech. 4, 523 (2009).

[11] Z.Q. Wang et al., Nature Comm. 4, 1395 (2013).

[12] J. Verbeeck et al., Nature 467, 301 (2010).

[13] P. Schattschneider et al., Phys. Rev. B 78, 104413 (2008).

[14] K. T. Moore and G. v.d. Laan, Rev. Mod. Phys. 81, 235 (2009).