ABSTRACT
The heat capacities of Gd(2)Zr(2)O(7) and Gd(2)Hf(2)O(7) both show sharp peaks in the vicinity of 0.77 K, consistent with the existence of long range magnetic order. They are superimposed in both cases on broader maxima centered at approximately 1 K, presumably due to short range spin correlations. Both compounds exhibit antiferromagnetic interactions, with Weiss constants of approximately -7 K. Comparisons are made to earlier results for the isomorphic compounds Gd(2)Ti(2)O(7) and Gd(2)Sn(2)O(7).
ABSTRACT
We have measured the low-temperature specific heat of the geometrically frustrated pyrochlore Heisenberg antiferromagnet Gd2Sn2O7 in zero magnetic field. The specific heat is found to drop exponentially below approximately 350 mK. This provides evidence for a gapped spin-wave spectrum due to an anisotropy resulting from single-ion effects and long-range dipolar interactions. The data are well fitted by linear spin-wave theory, ruling out unconventional low-energy magnetic excitations in this system, and allowing a determination of the pertinent exchange interactions in this material.
ABSTRACT
We describe a demountable (3)He melting curve thermometer, suitable for use at low temperatures with liquid helium samples at any pressure. The thermometer's resolution is 10 microK below 0.l K. It is designed to be particularly useful for experiments performed in magnetic fields.
