Narrow Results

Pauling's model of hydrogen disorder in water ice represents the prototype of a frustrated system. Over the years it has spawned several analogous models, including Anderson's model antiferromagnet and the statistical “vertex” models. Spin Ice is a sixteen vertex model of “ferromagnetic frustration” that is approximated by real materials, most notably the rare earth pyrochlores Ho₂Ti₂O₇, Dy₂Ti₂O₇ and Ho₂Sn₂O₇. These “spin ice materials” have the Pauling zero point entropy and in all respects represent almost ideal realisations of Pauling's model. They provide experimentalists with unprecedented access to a wide variety of novel magnetic states and phase transitions that are located in different regions of the field-temperature phase diagram. They afford theoreticians the opportunity to explore many new features of the magnetic interactions and statistical mechanics of frustrated systems. This chapter is a comprehensive review of the physics - both experimental and theoretical - of spin ice. It starts with a discussion of the historic problem of water ice and its relation to spin ice and other frustrated magnets. The properties of spin ice are then discussed in three sections that deal with the zero field spin ice state, the numerous field-induced states (including the recently identified “kagomé ice”) and the magnetic dynamics. Some materials related to spin ice are briefly described and the chapter is concluded with a short summary of spin ice physics.

New Mn12 single-molecule nanomagnets [Mn₁₂O₁₂(O₂CCHCl₂)(H₂O)₄]·2CH₂Cl₂·H₂O and [Mn₁₂O₁₂(O₂CCHCl₂)(H₂O)₄]·2CH₃C₆H₅·4H₂O and novel Mn18 complexes [M₁₈O₁₄(O₂CR)₁₈(hmp)₄(hmpH)₂(H₂O)₂] (R = Me, Et) have been synthesized and characterized by single crystal X-ray crystallography and dc- and ac-magnetic susceptibility measurements. Mn12 complexes show characteristic SMM properties, such as temperature-dependent out-of-phase ac-susceptibility. Mn18 does not show relaxation behaviors down to 2.0 K, but reveals magnetic anisotropy in reduced magnetization experiment.

Pauling's model of hydrogen disorder in water ice represents the prototype of a frustrated system. Over the years it has spawned several analogous models, including Anderson's model antiferromagnet and the statistical "vertex" models. Spin Ice is a sixteen vertex model of "ferromagnetic frustration" that is approximated by real materials, most notably the rare earth pyrochlores Ho₂Ti₂O₇, Dy₂Ti₂O₇ and Ho₂Sn₂O₇. These "spin ice materials" have the Pauling zero point entropy and in all respects represent almost ideal realisations of Pauling's model. They provide experimentalists with unprecedented access to a wide variety of novel magnetic states and phase transitions that are located in different regions of the field-temperature phase diagram. They afford theoreticians the opportunity to explore many new features of the magnetic interactions and statistical mechanics of frustrated systems. This chapter is a comprehensive review of the physics — both experimental and theoretical — of spin ice. It starts with a discussion of the historic problem of water ice and its relation to spin ice and other frustrated magnets. The properties of spin ice are then discussed in three sections that deal with the zero field spin ice state, the numerous field-induced states (including the recently identified "kagomé ice") and the magnetic dynamics. Some materials related to spin ice are briefly described and the chapter is concluded with a short summary of spin ice physics.