Spin-Ice

A spin ice is a magnetic substance that does not have a single minimal-energy state. It has magnetic moments as elementary degrees of freedom which are subject to frustrated interactions. By their nature, these interactions prevent the moments from exhibiting a periodic pattern in their orientation down to a temperature much below the energy scale set by the said interactions. Spin ices show low-temperature properties, residual entropy in particular, closely related to those of common crystalline water ice. The most prominent compounds with such properties are dysprosium titanate and holmium titanate. The orientation of the magnetic moments in spin ice resembles the positional organization of hydrogen atoms in conventional water ice.