Magnetic inhomogeneities in the quadruple perovskite manganite [Y${}_{2-x}$Mn${}_x$]MnMnMn${}_4$O${}_{12}$

Abstract

A combination of competing exchange interactions and substitutional disorder gives rise to magnetic inhomogeneities in the [Y${}_{2-x}$Mn${}_x$]MnMnMn${}_4$O${}_{12}$ $x=0.23$ and $x=0.16$ quadruple perovskite manganites. Our neutron powder scattering measurements show that both the $x=0.23$ and $x=0.16$ samples separate into two distinct magnetic phases; below T${}_1$ = 120 $\pm$ 10 K the system undergoes a transition from a paramagnetic phase to a phase characterised by short range antiferromagnetic clusters contained in a paramagnetic matrix, and below T${}_2$ $\sim$ 65 K, the system is composed of well correlated long range collinear ferrimagnetic order, punctuated by short range antiferromagnetic clusters. A sharp increase in the antiferromagnetic phase fraction is observed below $\sim$ 33 K, concomitant with a decrease in the ferrimagnetic phase fraction. Our results demonstrate that the theoretically proposed AFM phase is stabilised in the [Y${}_{2-x}$Mn${}_x$]MnMnMn${}_4$O${}_{12}$ manganites in the presence of dominant B-B exchange interactions, as predicted.

12 pages, 6 figures