Structure, Magnetism, Phase Transitions, and Disorder in Functional Materials: Insights from Neutron Diffraction and Complementary Methods

Functional materials often exhibit complex relationships between crystal structure, magnetism, disorder, and phase transitions. Understanding these relationships requires experimental techniques capable of probing atomic structure and magnetic interactions. Examples drawn from perovskite-type metal–organic frameworks, ferrite and perovskite oxides, and high-entropy oxides illustrate the role of neutron diffraction in resolving structural and magnetic complexity, alongside complementary characterisation approaches. Particular attention is devoted to structural and magnetic disorder, anomalous thermal expansion, pressure-induced phase transitions, hydrogen disorder, and symmetry variations. The complementary use of X-ray diffraction, Raman spectroscopy, magnetometry, Mössbauer spectroscopy, X-ray spectroscopy, and second-harmonic generation is also discussed. Together, these studies provide insight into structure–property correlations in functional materials across diverse material classes, with relevance to materials design.