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Jeffrey Quilliam - University of Waterloo, Canada & LPS, Orsay

Glassiness in dipolar and geometrically frustrated systems

I will discuss specific heat and magnetic susceptibility measurements of two distinct material systems that exhibit controversial glassy ground states. The dipolar Ising material LiHoxY1-xF4 has received a great deal of attention of late as a model magnetic system. In zero field and at low concentration of magnetic moments a spin glass state is expected to occur. However, the experimental proof of such a state has been heavily debated as of late with even an exotic spin liquid state having been observed at x=0.045. I will present results that show strong evidence of spin glass physics and argue that much of the difficulty in understanding this material comes from inherently slow dynamics, a result of the unusually large nuclear hyperfine coupling in the system.


In contrast, the geometrically frustrated material Gd3Ga5O12 or GGG exhibits a spin glass state that has evaded theoretical explanation for many years. A major question to resolve is whether the glassiness is a result of a sensitivity to small levels of disorder or whether there is a possible mechanism for a truly "disorder-free" spin glass state in GGG. We attempt to answer this question with measurements of a homologous series of Gd garnets.


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