Magnetism lanthanide ions

If the atomic model were rigorously correct, a lanthanide element would have the same magnetic moment in every material and crystalline environment. Of course, this is not the case, and more advanced methods have to be employed to determine the effect of the crystalline and chemical environment on magnetic moments with numerical precision. Examples of materials where the theory described above fails to give an accurate value for the lanthanide ion magnetic moment are ubiquitous. They include NdCos (Alameda et al., 1982), fullerene encapsulated lanthanide ions (Mirone, 2005), and lanthanide p)TO-chlores (Hassan et al., 2003). 

Local Structure of the Eu2+ Impurity. From the experimental perspective, the doping of lanthanide ions into solid state materials can be probed by different instrumental technics such as nuclear magnetic resonance (NMR),44 extended X-ray absorption fine structure (EXAFS),45,46 or electron paramagnetic resonance (EPR),47 which instead of giving a direct clue of the local geometry offers only data that can be corroborated to it. From the theoretical point of view,... 

Figure 1.2 Energetic structure of a Kramers lanthanide ion in a ligand field evidencing the effect of progressively weaker perturbation. The magnetic field effect is estimated assuming a 1T field.

Finally, we note that, to the best of our knowledge, only one report exists about EPR spectra of non-Kramers lanthanide ions in molecular magnets. In 2012, Hill and coworkers [51] performed a multifrequency study on powder and single crystal samples of NagHofWgOj H20, in both the pure form and when doped into the isostructural Y3+ derivative. While crystallizing in a triclinic unit cell, the symmetry of the lanthanide ion in this family is very close to Did. For this reason, susceptibility data had been previously fitted by a purely axial Hamiltonian [50]. 

Mononuclear Lanthanide Complexes Use of the Crystal Field Theory to Design Single-Ion Magnets and Spin Qubits... 

Modelling the Magnetic Properties of Lanthanide Single-Ion Magnets 29... 

Baldovi, J.J., Cardona-Serra, S., Clemente-Juan, J.M., Coronado, E., Gaita-Arino, A. and Palii, A. (2012) Rational design of single ion magnets and spin qubits based on mononuclear lanthanide complexes. Inorg. Chem., 51, 12565-12574. 

As pointed out by Sessoli and coworker in their review, a possible approach to increasing the energy barrier of lanthanide-based SMMs is by assembling together several lanthanide ions which interact magnetically either in a zero-dimensional structure (SMMs) or in a one-dimensional structure (Single-Chain Magnets) [26]. The last several years have indeed seen a flurry of results from synthetic chemists in this respect. Especially in our recent review about Dy-based SMMs, polynuclear... 

The structures and dynamic magnetic behaviours of 31-Dy4 and 31-Tb4 have been presented in Figure 3.22. Four lanthanide ions are aggregated in the grid-like metal core by a central p4-S and eight peripheral i2-S atoms from ethanethiol ligands [38]. The individual lanthanide centres occupy distorted six-coordinate [LnNS5] octahedral coordination environments. Ac susceptibilities measurements reveal pronounced temperature dependence with a series of maxima below 28 K, typical for SMM behaviour, in complex 31-Dy4. Furthermore, an... 

Three-positive lanthanide ions are not so promising if the objective is building bulk molecular magnets because of the internal character of 4f orbitals, which... 

At the beginning of this century slow magnetic relaxation in the paramagnetic phase of a ID system was reported for a Co2+ nitronyl-nitroxide chain [58]. The dynamics was under many respects very similar to that of SMMs and these ID systems were later named SCM to underline the analogies [9]. Since then an intense research activity, though not as spread out as for SMMs, has been devoted to SCMs. The interested reader can find extensive literature on the subject, including exhaustive reviews and a book chapter [59-63]. The aim here is to provide some basic concepts of the phenomenon and to introduce some selected examples of SCMs based on lanthanide ions. 

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