2011/08/25 by T. R. S. Prasanna, Prasanna, T. R. S.
Materials Science · Physics and Astronomy · #FOS: Physical sciences #Magnetic and transport properties of perovskites and related materials #Magnetic properties of thin films #Materials Science (cond-mat.mtrl-sci) #Physics of Superconductivity and Magnetism #cond-mat.mtrl-sci
paper · pdf · doi:10.48550/arxiv.1108.5106
Submitted for publication
arxiv created 2011/08/25 · openalex publication_date 2011/08/25 · arxiv updated 2011/08/26 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We address and resolve the fundamental contradiction that has existed from the earliest studies on magnetic phase transitions between theoretical models that ignore the role of thermal vibrations and represent the exchange interaction as a constant, Jij(0), and analysis of neutron diffraction data that always incorporates thermal vibrations even though it is also possible to analyze the same data by ignoring them. Of the two possibilities, ignoring thermal vibrations in both theoretical models and analysis of diffraction data leads to the latter giving different magnetic order parameters for different reciprocal lattice lines. This appears to be the first report of a unique consequence, viz. the assumption to neglect a physical phenomenon turns a single-valued experimental observable into a multiple-valued one where all values are equally valid. This assumption is clearly unacceptable and must be rejected. The second possibility of incorporating thermal vibrations in both leads to single-valued theoretical and experimental order parameters. Thus, analysis of neutron diffraction data constrain the exchange interaction in all theoretical models to be temperature dependent and represented as Jij(T). Additional experimental and theoretical evidences in support of this conclusion are presented.