Spin-induced ferroelastics with pyrochlore lattices

Abstract

Spin ordering in the geometrically frustrated magnetic materials with pyrochlore lattices is a key player in the emergent phenomena in modern condensed matter. A possible spin-ordered phases derived from the archetypical pyrochlore lattice were studied within the Landau conception of order parameter (OP) for case wavevector k = (0,0,0) associated with the center of the Brillouin zone of space group The existence of 20 low-symmetry types of spin-ordered phases is established. For each phase space group and set of proper and improper OPs are defined. Only one phase generated by irrep mГ2 + is not ferroelastic. The fundamental feature of spin-ordered phases in the pyrochlore lattices is that all remaining 19 phases found are improper ferroelastics. The Г5 + (a,a,a) shear deformation, involved in the formation of phases with space groups and is proved to be the only one that contributes to the formation of these rhombohedral distorted spin-ordered phases. Other types of shear deformations Г5 +(a,0,0) and Г5 +(a,b,b) are always cooperate with some of the Г3 + deformations at the formation of spin-ordered pyrochlores.