CCMP Seminar Series - Dr. Mark Senn

When: Tuesday, October 17, 2023, 3:30 PM - 4:30 PM
Where: G O Jones Building, Room 610, Mile End

Speaker: Dr. Mark Senn, University of Warwick

New insights into old problems: The electronic orderings and disorderings that underpin colossal magnetoresistance in the manganites

The phase diagrams of LaMnO3 perovskites have been intensely studied due to the colossal magnetoresistance (CMR) exhibited by compositions around the 3/8th doping level. However, phase segregation between ferromagnetic (FM) metallic and antiferromagnetic (AFM) insulating states, which itself is believed to be responsible for the colossal change in resistance under applied magnetic field, has prevented an atomistic-level understanding of the orbital ordered (OO) state at this doping level.

Here, through the detailed crystallographic analysis of the phase diagram of a prototype system (AMnA′3MnB4O12), we show that the superposition of two distinct lattice modes gives rise to a striping of OO Jahn-Teller active Mn3+ and charge disordered (CD) Mn3.5+ layers in a 1:3 ratio. This superposition only gives a cancellation of the Jahn-Teller-like displacements at the critical doping level. This striping of CD Mn3.5+ with Mn3+ provides a natural mechanism though which long range OO can melt, giving way to a conducting state.