Letter abstract
Nature Physics 2, 249 - 253 (2006)
doi:10.1038/nphys270
Subject Categories: Condensed-matter physics | Materials physics | Chemical physics
Zero-point entropy in stuffed spin-ice
G. C. Lau1, R. S. Freitas2, B. G. Ueland2, B. D. Muegge1, E. L. Duncan1, P. Schiffer2 and R. J. Cava1
The third law of thermodynamics dictates that the entropy of a system in thermal equilibrium goes to zero as its temperature approaches absolute zero. In ice, however, a 'zero point' or residual entropy can be measured—attributable to a high degeneracy in the energetically preferred positions of hydrogen ions associated with the so-called 'ice rules'1, 2. Remarkably, the spins in certain magnetic materials with the pyrochlore structure of corner-sharing tetrahedra, called 'spin ice', have an equivalent degeneracy of energetically preferred states, and also have a zero-point entropy3, 4, 5, 6, 7. Here, we chemically alter Ho2Ti2O7 spin ice by 'stuffing' extra Ho magnetic moments into otherwise non-magnetic Ti sites surrounding the Ho tetrahedra. The resulting series, Ho2(Ti2-xHox)O7-x/2, provides a unique opportunity to study the effects of increased connectivity between spins on a frustrated lattice. Surprisingly, the zero-point entropy per spin measured appears unchanged by these excess spins. The results suggest a chemical approach for studying ice-like frustration and other properties of the broad family of geometrically frustrated magnets based on the pyrochlore structure.
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
- Department of Physics and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA
Correspondence to: G. C. Lau1 e-mail: glau@princeton.edu
Correspondence to: P. Schiffer2 e-mail: schiffer@phys.psu.edu
Correspondence to: R. J. Cava1 e-mail: rcava@princeton.edu
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