In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

The ANNNI model — Theoretical analysis and experimental application

Structure and chemical bonding in zintl-phases containing lithium

A review is given of the physical properties, composition and crystal structure of intermetallic compounds formed between rare-earth elements and non-magnetic metals, with emphasis on the magnetic properties. Included are the properties of compounds in which the non-rare-earth component is a 4d or 5d transition element. Special consideration is given to the properties of pseudo-binary compounds. Results of magnetisation measurements, neutron diffraction and neutron scattering are discussed together with results derived from NMR, ESR and Mossbauer effect spectroscopy. An evaluation is given of the relevance of the experimental results with respect to different types of exchange interactions in this class of intermetallics. Special consideration is also given to the influence of crystal field effects on the magnetic properties and, furthermore, to the occurrence of intermediate valences in several of the compounds of Ce, Sm, Eu and Yb.

https://iopscience.iop.org/article/10.1088/0034-4885/42/8/003/pdf

Intermetallic compounds of rare earths and non-magnetic metals

46 structure types of binary and ternary intermetallic compounds have been derived from the well known, simple aristotype AlB 2 . Many compounds with the general compositions RX 2 , RT 2 , R7X, and R 2 TX 3 (R = alkaline earth, rare earth or actinoid metal: T = transition metal; X = main group element) belong to this family. The structural similarities between these compounds are manifested by an ordering of the transition metal atoms and main group element atoms on the boron positions of the AlB 2 type. Also an ordering of vacancies on the boron positions occurs in some compounds. Striking structural motifs of the RX 2 , RT 2 , RTX, and R 2 TX 3 compounds are planar or puckered six-membered rings consisting of X 6 , T 6 . T 3 X 3 , and T 2 X 4 separated by the respective R atoms The crystal chemical relationships between these compounds are discussed on the basis of a group-subgroup scheme in the concise and compact Barnighausen formalism with respect to the aristotype AlB 2 . Two different branches of AlB 2 related structures are discussed. In the first, the hexagonal/trigonal branch, six-membered rings carry at least a three-fold axis, while in the orthorhombic/ monoclinic branch the distortions are more pronounced. The pseudo-hexagons show significant tilting and a loss of hexagonal/trigonal symmetry. Significant variations of the chemical bonding occur for some structure types, and therefore they may only be considered to be isopointal rather than isotypic. These isopointal conversions are based on a gradual changeover from two- to three-dimensionally infinite polyanions. Besides the group theoretical group-subgroup scheme we also discuss chemical bonding in these AlB 2 related intermetallic compounds.

Penelope Schobinger-Papamantellos

Papers

Neutronenbeugungsuntersuchung der Atomverteilung von Mg 17 Al 12

Magnetic ordering and phase transitions of RFe4Al8 (R=La, Ce, Y, Lu) compounds by neutron diffraction

Magnetic properties of DyMn6Ge6 studied by neutron diffraction and magnetic measurements

Crystal structure of the compound DyGe3

A neutron diffraction study of the magnetic ordering of TmMn6Ge6