Kavli Affiliate: Kristin A. Persson
| First 5 Authors: Joya A. Cooley, Gregor Dairaghi, Guy C. Moore, Matthew K. Horton, Emily C. Schueller
| Summary:
Co$_{1-x}$Mn$_x$Cr$_2$O$_4$ crystallizes as a normal spinel in the cubic $Fd
overline{3}m$ space group, and the end members have been reported to display a
region of collinear ferrimagnetism as well as a low-temperature spin-spiral
state with variable coherence lengths from 3 nm to 10 nm in polycrystalline
samples. Here, we present the synthesis of the entire solid solution, and data
showing that the ferrimagnetic ordering temperature as well as the spin-spiral
lock-in temperature are tunable with the Co/Mn ratio. The peak magnetocaloric
entropy change was determined to be $Delta S_M$ = -5.63 J kg$^{-1}$ K$^{-1}$
in an applied magnetic field change of $Delta H$ = 0 T to 5 T for the Mn
end-member at the ferrimagnetic ordering temperature. Using density functional
theory (DFT), we explore the shortcomings of the magnetic deformation proxy to
identify trends in $Delta S_M$ across composition in this spinel system, and
explore future extensions of theory to address these discrepancies.
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