My current research interests center around low temperature magnetism, especially solids which exhibit magnetic order due to the magnetic dipole interaction (rather than the more familiar exchange interaction), and magnetic frustration. In the case of the dipolar magnets, the Hamiltonian for the dipole force is known exactly, so one can hope to make critical comparisons between experiment and theory. The conclusions may have implications for our understanding of familiar exchange-coupled magnets such as ferrites. We have studied the susceptibility and spontaneous magnetization below 1 K of several axial materials, including the rare earth ethyl sulfates. These are of interest because some of them provide very good laboratory examples of the Ising model, but with dipolar interactions. We have also studied two classes of cubic dipolar ferromagnets: the Cs2Na(RE)(NO2)6 and Cs2Na(RE)Cl6 compounds. These form for the whole series of rare earth (RE) elements, and have a magnetic order which is determined by lattice symmetry alone. In contrast, the rare earth phosphomolybdates or (RE)PO4(MoO3)12.30H20 form another cubic system, this time with diamond symmetry, which we find to be dipolar antiferromagnets with very large, macroscopically observable quantum spin fluctuations. The difference with the cubic ferromagnets is due purely to symmetry. These compounds are the first to show spin fluctuations directly in the susceptibility. Most recently we have studied the cubic K(RE)3F10 compounds, some of which contain three mutually orthogonal Ising lattices of magnetic ions. Despite the presence of antiferromagnetic exchange, and dipole-dipole interactions which favor antiferromagnetism, several of them are ferromagnets

A second area of investigation is magnetic frustration. This phenomenon occurs when an exchange-coupled magnetic ion cannot satisfy all of its magnetic bounds, and hence does not know what direction to point (it is "frustrated"). This effect plays an important part in the behavior of spin glasses, but also occurs in certain materials which have long range crystalline order. We have studied several of the rare earth pyrochlore materials, many of which are highly frustrated. By studying the magnetic and thermal properties of these materials, we hope to find out whether they ultimately order magnetically at sufficiently low temperatures, and if so, whether the order is long-range or glassy.

In both these areas of research a 3He-4He dilution refrigerator cools samples down to 7 mK absolute. Magnetic properties are measured using special low temperature fluxgate magnetometers, and also a SQUID magnetometer. We have semi-adiabatic calorimeters to measure thermal properties, one for dilution refrigerator temperatures, and a second for the range 0.5 K to 30 K. The crystal structure of new sample materials is characterized using an automated powder x-ray diffractometer with a 10 K cold stage.

Honors and Awards
Linton R. Corruccini


Selected Publications

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