טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentOfer Oren
SubjectThe Impact of Perturbations on Frustrated Magnets
DepartmentDepartment of Physics
Supervisor Professor Amit Keren
Full Thesis textFull thesis text - English Version


Abstract

Liquids are expected to crystallize at low temperatures. The only exception known is Helium, which can remain a liquid at 0 K, due to quantum fluctuations. Similarly, the spins in a magnet are expected to order at a temperature set by their Curie-Wiess temperature,θCW. Geometrically frustrated magnets represent an exception. In these systems, the pair-wise spin interactions cannot be simultaneously minimized due to the lattice symmetry. This frustration leads to unconventional magnetic ground states and macroscopic degeneracies.

In antiferromagnets, the spins align anti-parallel with each other. In the case of a triangular lattice, only two spins can align anti-parallel leaving the third spin frustrated and "baffled" not knowing what to do. The question we are interested in is: what will happen in this situation. So far, we've studied three examples of triangular frustrated lattices, the 2-dimensional kagome Zn-paratacamite, and the 3-dimensional

pyrochlore lattices Y2Mo2O7 and Tb2Ti2O7. In the Zn-paratacamite we've found that the spins continue to fluctuate down to 60mK meaning no spin freezing, also µSR didn't detect any lattice deformation, NMR T1 revealed that the excitation spectrum is gapless. In the Y2Mo2O7 pyrochlore, we found that appearance of two (with a hint of a third) non-equivalent Y sites indicating two (or 3) domains or phases, high resolution x-ray powder diffraction revealed a magneto-elastic mechanism.