2012/11/08 by Hirai, Shigeto, Santos, Antonio M. dos, Shapiro, Maxwell C. +6
#FOS: Physical sciences #Strongly Correlated Electrons (cond-mat.str-el)
paper · doi:10.48550/arxiv.1211.1667
We present x-ray, neutron scattering and heat capacity data that reveal a coupled first-order magnetic and structural phase transition of the metastable mixed-valence post-spinel compound Mn3O4 at 210 K. Powder neutron diffraction measurements reveal a magnetic structure in which Mn3+ spins align antiferromagnetically along the edge-sharing a-axis, with a magnetic propagation vector k = [1/2, 0, 0]. In contrast, the Mn2+ spins, which are geometrically frustrated, do not order until a much lower temperature. Although the Mn2+ spins do not directly participate in the magnetic phase transition at 210 K, structural refinements reveal a large atomic shift at this phase transition, corresponding to a physical motion of approximately 0.25 Å even though the crystal symmetry remains unchanged. This "giant" response is due to the coupled effect of built-in strain in the metastable post-spinel structure with the orbital realignment of the Mn3+ ion.