A Preliminary Survey of the Paramagnetic Resonance Phenomena observed in Rare Earth Ethyl Sulphates

Electron spin echo spectra and characterization of electronic ground states for lanthanide ions in acidic water:ethanol glasses

X-band EPR absorption spectra were obtained by field-swept echo-detection for 10 mM Ce³⁺, Nd³⁺, Sm³⁺, Tb³⁺, Er³⁺, Tm³⁺, and Yb³⁺ in glassy acidic 1:1 water:ethanol at 4.2 to 6 K. The slowly-varying signals extend over thousands of gauss and are more readily detected by spin echo than by continuous wave EPR. For lanthanide ions spin-orbit coupling is strong and J is a good quantum number. The microwave power required to achieve a π/2 pulse depends on quantum numbers J and m_J and the g_J for the levels involved in the EPR transition, so it can be used to characterize the electronic ground state. For Nd³⁺, Sm³⁺, Er³⁺, and Tm³⁺ the power required for a π/2 pulse is consistent with values calculated for the expected value of g_J and transitions involving m_J = ±1/2 or m_J = ±1,0. However for Ce³⁺, Gd³⁺, Tb³⁺, and Yb³⁺ the microwave power required for a π/2 pulse is larger than predicted. For Ce³⁺, Tb³⁺, and Yb³⁺ it is proposed that mixing of levels results in contributions to the transitions from higher values of m_J. For Gd³⁺ the discrepancy is attributed to overlapping transitions with varying values of m_J.

Magnetic properties of a Kramers doublet. An univocal bridge between experimental results and theoretical predictions

The magnetic response of a Kramers doublet is analyzed in a general case taking into account only the formal properties derived from time reversal operation. It leads to a definition of a matrix G (gyromagnetic matrix) whose expression depends on the chosen reference frame and on the Kramers conjugate basis used to describe the physical system. It is shown that there exists a reference frame and a suitable Kramers conjugate basis that gives a diagonal form for the G-matrix with all non-null elements having the same sign. A detailed procedure for obtaining this canonical expression of G is presented when the electronic structure of the KD is known regardless the level of the used theory. This procedure provides a univocal way to compare the theoretical predictions with the experimental results obtained from a complete set of magnetic experiments. In this way the problems arising from ambiguities in the g-tensor definition are overcome. This procedure is extended to find a spin-Hamiltonian suitable for describing the magnetic behavior of a pair of weakly coupled Kramers systems in the multispin scheme when the interaction between the two moieties as well as the individual Zeeman interaction are small enough as compared with ligand field splitting. Explicit relations between the physical interaction and the parameters of such a spin-Hamiltonian are also obtained.