Physical Society Colloquium

Powder diffraction in high magnetic fields:
from a new tool to novel physics

Vitalij Pecharksy

Iowa State University

Temperature and/or pressure induced polymorphism is common compared to structural rearrangements triggered by a magnetic field. While the former is routinely probed in-situ, especially by temperature dependent powder diffraction, the most common tools employed in detecting magnetic field induced polymorphic transformations are bulk field-dependent measurements of the physical properties, such as the electrical resistance, magnetization and strain. On one hand, discontinuities in the behavior of these macroscopic properties serve as suitable evidence of a structural phase transition, but on the other hand, they provide no clues about the atomic-scale mechanism. Furthermore, there are cases when temperature alone cannot trigger a transformation. By successfully coupling a rotating anode powder diffractometer with a continuous-flow cryostat and a split-coil superconducting magnet we are now capable of obtaining excellent Rietveld-quality powder diffraction data between 2.5 and 315 K in 0 to 4 T magnetic fields. A typical experiment can be carried out in ~10 minutes (usually sufficient to quantify phase content and determine changes in unit cell parameters) or in a few hours (if detailed information about individual atomic parameters is required). Both subtle and massive magnetic field-induced structural changes can be detected, providing much needed structural data in order to develop a better understanding of structure-property relationships of solids.

This research was supported by the Division of Materials Science of the Office of Basic Energy Sciences of the US DOE under contract No. W-7405-ENG-82.