A. E. Usachev

Ligand ENDOR of Cr3+ and Yb3+ ions in Cs2NaInCl6

The ligand and quadrupole interactions parameters have been measured at 4.2 K by ENDOR for three shells of 35,37Cl, 133Cs and 23Na neighbours around Cr3+ and Yb3+ substitutional impurities. The ligand interaction parameters were analysed by means of expressions for spin densities obtained by the configurational interaction method. The quadrupole interaction parameters have been discussed in terms of a point-dipole model, and local deformation around the magnetic ions being taken into account.

Microphase separation and magnetic Jahn-Teller polarons in LaSrAl1−xCuxO4−δ

An EPR study of the solid solutions LaSrAl1−xCuxO4, which are isostructural to La2CuO4, shows that microphase separation of the structure occurs already at small copper concentrations (x≈0.01). A phase enriched with Cu appears along with a phase of La2AlO4, which contains isolated CuO6 centers. It is established that the nature of the states and the deformations of the CuO6 centers is determined by internal Jahn-Teller factors. When x⩽0.1, EPR signals are detected for new dynamic centers, which are identified as CuO6 Jahn-Teller centers with a hole delocalized among the four in-plane oxygen ions (the total spin S=1). When 0.1⩽x<1, local CuO6− hole centers transform into magnetic Jahn-Teller polarons, which include five or more CuO6 fragments, in the copper phase of the structure. Their transformations and the conditions for observing them are discussed.

Spin-spin interactions of Ce3+ ions in the elpasolite crystal Cs2NaInCl6

The EPR method is used to study at T=4.2 K crystals of Cs2NaInCl6:Ce3+ (1 mol %) at which have elpasolite structure. A solitary cubic Ce3+ center and three types of Ce3+-Ce3+ pairs were observed, for which the spin-spin interaction parameters D and E were determined. It is established that deformation of the local structure results in a shift {Δg} of the pair relative to the g-factor of the solitary center. Models of the solitary center and the three types of Ce3+-Ce3+ pairs are discussed, as well as the nature of the spin-spin interactions in the pairs. The non-dipole nature of the interactions is established. Possible chains for the creation of an indirect exchange between the Ce3+ ions are considered.

X-ray diffractometry and electrical conductivity of the ceramics LaSrAl(Cu,Ni)O4

A continuous series of solid solutions LaSrAL1−xMexO4 (Me = Cu, Ni) has been investigated by x-ray diffractometry and by electrical conductivity measurements. The results are of interest from the standpoint of the theory of close-packing, percolation theory, and the theory of the cooperative Jahn-Teller effect.