Chapter 10
Measuring Atomic Magnetic Moments
in Magnetic Nanostructures Using X-Ray
Magnetic Circular Dichroism (XMCD)
Chris Binns, José Angel de Toro, and Peter Normile
Abstract The chapter describes the development of X-ray magnetic circular
dichroism (XMCD) using circularly polarised soft X-ray photons from synchrotron
sources. Following the derivation of X-ray absorption sum rules for magnetic materials, the technique became a powerful probe of magnetism able to separately measure
the atomic and spin orbital magnetic moments independently for each magnetic
element in the sample. The majority of the experiments have focused on the Labsorption edges of transition metals and the method has been particularly useful in
identifying the source of enhanced magnetic moments in nanostructures. The chapter
illustrates the power of the method with a specific example, that of Fe@Cr core–
shell nanoparticles with different Cr shell thicknesses. Here, it was shown that at
least two Cr atomic layers are required to see the onset of the exchange bias effect at
the ferromagnetic–antiferromagnetic interface. The future perspectives of the technique are described including spatially resolved XMCD and time-resolved XMCD
measurements.
10.1 Introduction
X-ray magnetic circular dichroism (XMCD) has emerged as a powerful tool that is
capable of measuring element-specific atomic orbital and spin magnetic moments in
materials. The technique has enabled some important breakthroughs in the understanding of the magnetic behaviour of nanostructures. Magnetic circular dichroism in
the UV band has been known since the nineteenth century but X-ray magnetic circular
dichroism began to be of interest as a magnetic measurement method in the 1970s.
Erskine and Stern predicted in 1975 that circularly polarised X-rays could provide
information on the valence band spin polarisation of Ni [1]. In 1987, a measurement
of the transmission of synchrotron radiation through thin Fe films showed a difference
C. Binns (B) · J. A. de Toro · P. Normile
Instituto Regional de Investigación Científica Aplicada (IRICA), Av. Camilo José Cela, 1, 13005
Ciudad Real, Spain
e-mail: christopher.binns@uclm.es
© Springer Nature Switzerland AG 2021
D. Peddis et al. (eds.), New Trends in Nanoparticle Magnetism,
Springer Series in Materials Science 308,
https://doi.org/10.1007/978-3-030-60473-8_10
241
Measuring Atomic Magnetic Moments
in Magnetic Nanostructures Using X-Ray
Magnetic Circular Dichroism (XMCD)
Chris Binns, José Angel de Toro, and Peter Normile
Abstract The chapter describes the development of X-ray magnetic circular
dichroism (XMCD) using circularly polarised soft X-ray photons from synchrotron
sources. Following the derivation of X-ray absorption sum rules for magnetic materials, the technique became a powerful probe of magnetism able to separately measure
the atomic and spin orbital magnetic moments independently for each magnetic
element in the sample. The majority of the experiments have focused on the Labsorption edges of transition metals and the method has been particularly useful in
identifying the source of enhanced magnetic moments in nanostructures. The chapter
illustrates the power of the method with a specific example, that of Fe@Cr core–
shell nanoparticles with different Cr shell thicknesses. Here, it was shown that at
least two Cr atomic layers are required to see the onset of the exchange bias effect at
the ferromagnetic–antiferromagnetic interface. The future perspectives of the technique are described including spatially resolved XMCD and time-resolved XMCD
measurements.
10.1 Introduction
X-ray magnetic circular dichroism (XMCD) has emerged as a powerful tool that is
capable of measuring element-specific atomic orbital and spin magnetic moments in
materials. The technique has enabled some important breakthroughs in the understanding of the magnetic behaviour of nanostructures. Magnetic circular dichroism in
the UV band has been known since the nineteenth century but X-ray magnetic circular
dichroism began to be of interest as a magnetic measurement method in the 1970s.
Erskine and Stern predicted in 1975 that circularly polarised X-rays could provide
information on the valence band spin polarisation of Ni [1]. In 1987, a measurement
of the transmission of synchrotron radiation through thin Fe films showed a difference
C. Binns (B) · J. A. de Toro · P. Normile
Instituto Regional de Investigación Científica Aplicada (IRICA), Av. Camilo José Cela, 1, 13005
Ciudad Real, Spain
e-mail: christopher.binns@uclm.es
© Springer Nature Switzerland AG 2021
D. Peddis et al. (eds.), New Trends in Nanoparticle Magnetism,
Springer Series in Materials Science 308,
https://doi.org/10.1007/978-3-030-60473-8_10
241