Ch. Cartier dit Moulin

XMCD Measurements in a high TC molecular based magnet

The molecular based magnet CsI[NiIICrIII(CN)6]. 2H2O is a ferromagnet with a Curie temperature TC = 90 K. Its structure consists of face centred cubic lattice of NiII ions connected by Cr(CN)6 entities. We have recorded X-ray Magnetic Circular Dichroism (XMCD) at nickel L2,3 edges. It clearly evidences that nickel II is in a high spin configuration and ferromagnetically coupled to the surrounding CrIII. Through Crystal Field Multiplet calculations, we have determined the precise ground state of NiII. Special attention has been paid to the magnetic anisotropy that complicates the calculation of the cross section for a powder. By using sum rules derived for XMCD, it has been possible to extract the orbital and spin contributions to the total magnetic moment. A too small magnetic moment is found on nickel. A complete calculation taking into account the multiplet coupling effect and the covalent hybridisation showed that hybridisation cannot be responsible for the experimental low nickel magnetic moment. The origin of this effect is discussed.

Spin Transition Studied by XANES Spectroscopy: A Multiple Scattering Approach

Iron ion in Fe(II)(o-phenantroline)2(NCS)2 presents an abrupt and complete spin transition t2g4eg2[S=2] → t2g6eg0[S=0] around T=170K. We have recorded iron K-edge spectra above and below 170K and it is found that they are strongly modified during the transition. The strong XANES modifications for the two spin phases can find their origin in electronic configuration changes or in structural modifications. We apply Full Multiple Scattering theory to sort out the origin of the modifications.

Soft x-ray magnetic circular dichroism in molecular based magnet

Abstract The molecular based magnet Cs I [Ni II Cr III (CN) 6 ]·2H 2 O is a ferromagnet with a Curie temperature T C = 90 K. Its structure consists of face centered cubic lattice of Ni II ions connected by Cr(CN) 6 entities. We have recorded X-ray Magnetic Circular Dichroism (XMCD) at the L 2,3 edges of Ni II . Through Crystal Field Multiplet calculation we have determined the total magnetic moment carried by the Ni II . By using sum rules derived for XMCD, it has been possible to extract orbital and spin contributions to the total magnetic moment. A somewhat too small magnetic moment is found on nickel. A complete calculation taking into account the multiplet coupling effect and the covalent hybridization allowed to determine the precise ground state of nickel and showed that hybridization with surrounding nitrogen atoms is not responsible for the experimental low nickel magnetic moment.

Soft X-ray magnetic circular dichroism in molecular based magnets

Abstract The molecular based magnet CsI[NiIICrIII(CN)6]·2H2O is a ferromagnet with a Curie temperature TC = 90 K. Its structure consists of face centered cubic lattice of NiII ions connected by Cr(CN)6 entities. We have recorded X-ray Magnetic Circular Dichroism (XMCD) at the L2,3 edges of NiII. It clearly evidences that nickel II is in a high spin configuration and ferromagnetically coupled to the surrounding CrIII. Through Crystal Field Multiplet calculation we have determined the total magnetic moment carried by the NiII. By using sum rules derived for XMCD, it has been possible to extract the orbital and spin contributions to the total magnetic moment. A somewhat too small magnetic moment is found on nickel. A complete calculation taking into account the multiplet coupling effect and the covalent hybridization allowed to determine the precise ground state of nickel and showed that hybridization with surrounding nitrogen atoms is not responsible for the experimental low nickel magnetic moment.