"Giant atomic displacement at a magnetic phase transition in metastable Mn3O4 "

S. Hirai: A. M. dos Santos, M. C. Shapiro, J. J. Molaison, N. Pradhan, M. Guthrie, C. A. Tulk, I. R. Fisher, and W. L. Mao; Phys. Rev. B 87, 01/14/13.

Additional Authors: A. M. dos Santos, M. C. Shapiro, J. J. Molaison, N. Pradhan, M. Guthrie, C. A. Tulk, I. R. Fisher, and W. L. Mao

Abstract:

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 postspinel compound Mn3O4 at 210 K. Powder neutron diffraction measurements reveal a magnetic structure in which Mn 3+ 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 postspinel structure with the orbital realignment of the Mn3+ ion.