Magnetically frustrated ground states in insulators and metals

In some magnetic materials, competing exchange interactions between localized spins give rise to complex magnetic order, spin-ice or quantum spin liquid state. These systems are classified as magnetically frustrated systems. Magnetic frustration are traditionally studied in magnetic insulators where frustrated nearest neighbor exchange interactions are realized either in a geometrically frustrated lattice like kagome, hyper-kagome and pyrochlore lattice or through bond-dependent, anisotropic, frustrated magnetic super-exchange like Kitaev exchange. I will discuss physics of magnetic frustration in the context of Kitaev physics visualized in honeycomb lattice iridates (Na2IrO3 and Li2IrO3). Honeycomb lattice iridates order antiferromagnetically with a very unconventional magnetic structure due to strong anisotropic Kitaev exchange present in the iridate lattice. Magnetism in the honeycomb iridates can be tuned by chemical doping to understand underlying magnetic exchange. 

Realizing magnetic frustration in metals rather posses a bigger challenge due to presence of longer range exchange interaction. We have been working on the rare earth intermetallics with geometrically frustrated magnetic sub-lattice e.g. ZrNiAl-type YbAgGe, CeRhSn etc. to understand the effect of magnetic frustration in metals. We have investigated a Gd-based magnet with ZrNiAl-type structure to study the effect of magnetic frustration on J=7/2 multiplet instead of Ce3+ or Yb3+ doublet.