Chemical Structure / Physical Property Relationships in Organic Solids

J.L. Musfeldt, University of Tennessee, DMR 0600089

• The finding that hydrogen bonding can control both long range and local structure while providing significant magnetic exchange pathways has generated significant interest in the properties of low-dimensional coordination polymers such as Cu(pyz)2HF2BF4.

• At the same time, the magnetic properties of Cu(pyz)2HF2BF4 are highly tunable, with magnetization saturating at experimentally realizable magnetic fields.

• This makes Cu(pyz)2HF2BF4 a prototype for fundamental studies of quantum magnetism and an important foil for copper oxide materials, where the energy scales are much higher and often inaccessible.

• In order to probe magnetoelastic coupling in a model coordination polymer, we measured the vibrational properties of Cu(pyz)2HF2BF4 through the 20 T magnetically-driven transition.

• The out-of-plane pyrazine ring deformation and bending modes display clear frequency shifts with applied field. In contrast, the BF4-related modes are rigid.

• Magnetoelastic interactions do not saturate. Instead, they increase with applied magnetic field, even above 20 T.

• A vibrational mode analysis provides the microscopic basis for understanding this field-driven elastic distortion.

Brown et al, Inorg. Chem (2007); Goddard et al, PRB (2008), Unpublished Work

Magnetic Field (T)

Education and Human Development J.L. Musfeldt, University of Tennessee, DMR 0600089

• Broad, interdisciplinary training of students in materials spectroscopy

• Close interaction and collaboration with materials design and theory groups. Active collaborations at Argonne National Laboratory and the National High Magnetic Field Laboratory.

• 14 undergraduates and 3 high school students over a 10 year period.

• ~40% female participation, with both African American and Hispanic American female students.

• Projects in the area of organic superconductivity, vibrational dynamics of endohedral fullerenes, and magnetoelastic interactions in coordination polymers provide group members with important opportunities at every level of seniority and interest.

High school, undergraduate, and graduate students as well as postdoctoral researchers have been involved in these projects.