X-Ray Magnetic Circular Dichroism of Dinuclear Cobalt Dyprosium Compounds

X-ray magnetic circular dichroism (XMCD) has been applied to investigate the magnetic properties of CoII(btmp)2(µ-piv)DyIII(piv)2 and to probe how these properties are dependent on the interaction between the Co and Dy.
XMCD is an element specific measurement based on X-ray absorption spectroscopy (XAS), with the use of circularly polarised X-rays while an external magnetic field is applied to the sample. In an XAS experiment, an incident X-ray excites a core electron to the valence band; the energy of the incident X-ray is discrete and characteristic of the element and transition which the electron undertakes. In XMCD the absorption intensity is dependent on the availability of spin up and spin down holes in the valence band. Varying the direction of the external magnetic field or polarisation enables the production of difference spectra which are characteristic of the ground state magnetic structure [1].
Lanthanide single-molecule magnets (SMM) are an area of significant interest due to the improvements in slow relaxation of the magnetisation achieved thus far [2], and their potential for enhancing information storage density, enabling the production of smaller electronic devices. ... mehrCoII(btmp)2(µ-piv)DyIII(piv)2 possesses properties of a SMM. Herein, Co has a coordination of 5 in a distorted square pyramid polyhedral and Dy is within a 9-fold coordinated muffin type polyhedral [3]. To elucidate the dependence of magnetic properties in this SMM on the interaction between Co and Dy, CoII(btmp)2(µ-piv)YIII(piv)2 and ZnII(btmp)2(µ-piv)DyIII(piv)2, molecules where Y and Zn have been substituted for Dy and Co respectively. Magnetic properties of all three molecules were characterised by classical magnetometry. For Co-Dy the magnetic susceptibility decreases from 250 K to a minimum at ca. 12.5 K, where a sharp change denotes a transition in magnetic behaviour.
XMCD experiments at the Co L2,3 and Dy M4,5¬ edges were performed on the three compounds described above to investigate the magnetic structures of Co and Dy. Data were collected under a magnetic field of + 1.8 T and -1.8 T and with parallel and antiparallel circularly polarised X-rays. Samples were prepared for measurement by grinding into powder and pressing into indium foil. Measurements were performed at Beamline 6.3.1. at the Advanced Light source, Lawrence Berkeley National Laboratory, USA. Initial observations indicate Co–Dy interactions evident in the room-temperature Co L2,3 XAS. These interactions will be discussed in light of Dy M4,5¬ edge XMCD at 25 and 10 K [4].