Synopsis

# Appreciate the imperfections

Physics 3, s16
Crystalline order is not a necessary condition for magnetic quantum tunneling in a molecular magnet.

When a crystalline material is being developed for large-scale applications, the question arises: what if the material isn’t a perfect crystal? This is a particularly relevant issue for crystals of molecular magnets—molecules that carry a large spin—as they have been touted as potential quantum information storage systems.

In a paper appearing in Physical Review B, Chiara Carbonera and colleagues at the Instituto de Ciencia de Materiales de Aragón (CSIC-U. Zaragoza) in Spain, in collaboration with scientists at several institutions in Europe, present a careful study of the role of disorder on quantum tunneling in single-molecule magnet crystals. Quantum tunneling is the field-induced tunneling of molecular spins from one quantum state to the other, a process that could provide a way of storing information in the crystal.

Carbonera et al. focus on a crystal of $Mn12$ benzoate, which is one of the most widely studied of the molecular magnets. The group took care to prepare their crystals without solvent molecules, known as a source of local disorder. This allows them to compare two extreme situations: a highly crystalline structure, and one that is rapidly cooled to yield long-range disorder.

Carbonera et al. combine several complimentary experimental techniques—magnetic susceptibility, electron-spin resonance, neutron scattering—to reveal that, contrary to expectation, crystalline disorder has only minimal effect on quantum tunneling. In fact, disorder appears to make the $Mn12$ spins tunnel faster than they would have in a perfect crystal, which is good news should these materials turn out to be a viable system for quantum information processing. – Jessica Thomas

Magnetism

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