Element Specific Magnetometry Combining X-ray Circular with Linear Dichroism: Fundamentals and Applications

Abstract

This article gives an overview of the use of X-ray absorption spectroscopy to characterize the magnetic properties for technologically important, low dimensional magnetic materials. An overview is given both for the experimental hardware, the measurements and the analysis of the spectra. The information obtained is discussed for metallic and semiconducting systems, using both the X-ray magnetic circular dichroism and the X-ray linear magnetic dichroism spectroscopy. DOI: 10.12693/APhysPolA.127.831 PACS: 78.70.Dm, 78.20.Ls, 75.50.Pp, 75.50.Tt Short historic overview of the XMCD techniqueTo start this historical outline one should mention that although the X-ray magnetic circular dichroism (XMCD) technique is relatively young, the magneto-optical eect characteristic of the interaction between light and a magnetic medium was studied already in the nineteenth century, when several key discoveries were made enabling the development of new experimental techniques and thus studying so far unknown properties of matter. Let's start with Augustin Fresnel, who was the rst one to envision the existence of circular and elliptical light polarization.In his equations on light waves he described how light polarized in circular or elliptical states can be produced At about the same time, in 1895, investigating the phenomenon of cathode rays Roentgen discovered invisible, high-energy radiation in the spectral range from ultraviolet to gamma rays. This discovery initiated research on the physical properties of X-ray radiation and its interaction with matter. Despite the fact that the discovery of X-rays was made after the discovery of magneto-optical eects, it took still several decades for magneto-optics experiments based on X-rays.The rst theoretical predictions of a strong magnetic circular dichroism eect has been made in 1975 by E.A.(831)

Stable antiferromagnetic nanocrystals for room temperature applications: the case of iron nitride

“…17 Using Fe L-edge X-ray absorption spectroscopy in the XLMD mode, it is possible to also record the Fe atom antiferromagnetic response. 18,19 In an XLMD experiment the absorption coefficient is recorded with the magnetisation parallel and perpendicular to the X-ray beam polarization plane. 18 The difference between the two spectra is non zero in the presence of a non zero magnetic moment on the Fe atoms even if the atomic spins between neighbouring atoms have an anti-parallel arrangement.…”

“…Using Fe L-edge X-ray absorption spectroscopy in the XLMD mode, it is possible to also record the Fe atom AFM response. 19 It has been previously shown that indeed the L-edge XLMD signal strength, for the 3d transition elements, follows a quadratic dependence versus the strength of the atom magnetic moments. 18 Here we follow a similar approach as the one applied in this earlier work to obtain a measure of the value of the Fe atom magnetic moments.…”

“…3, together with the data from a magnetic standard where Fe is in the metallic bcc state. 19,25,30 It is observed that for all samples containing FM nanocrystals even in the case where a 6 T magnetic field is applied, only a FM spin magnetic moment of less than 1 m B per Fe atom is observed. For all Fe n N phases, based on theory, we expect values of the magnetic moment of more than 1.5 m B per Fe atom (Fig.…”