Complex Ferrimagnetism and Magnetoresistance Switching in Ca-Based Double Double and Triple Double Perovskites

Abstract

Cation ordering in ABO3 perovskites can lead to interesting and useful phenomena such as ferrimagnetism and high magnetoresistance by spin polarized conduction in Sr2FeMoO6. We have used high pressures and temperatures to synthesize the cation ordered AA′BB′O6 perovskites CaMnFeReO6, CaMnMnReO6, and Ca(Mn0.5Cu0.5)FeReO6. These have columnar A/A′ and rocksalt B/B′ cation orders, as found in the recently discovered double double perovskite MnNdMnSbO6, and partial Mn/Cu order over tetrahedral and square planar A′ sites in Ca(Mn0.5Cu0.5)FeReO6 demonstrates that 'triple double' cation order is possible. Neutron diffraction reveals complex ferrimagnetic orders in all three materials; CaMnFeReO6 and Ca(Mn0.5Cu0.5)FeReO6 have large room temperature magnetizations with low temperature switching of magnetoresistance in the latter material, and CaMnMnReO6 displays a high coercivity of 1.3 T at low temperatures.

Intrinsic Triple Order in A‐site Columnar‐Ordered Quadruple Perovskites: Proof of Concept

“…Our structural analysis with neutron diffraction confirmed this and gave the following composition of the main perovskite phase: Dy 2.2 Cu 0.85 Mn 4.95 O 12 . Synthesis conditions (such as, pressure, annealing temperature, and cooling rates) should, of course, have effects on the degree of cation ordering as was found in Ca 2 CuMnFe 2 Re 2 O 12 . However, the general tendency should be primarily determined by the cation nature, size, and coordination preferences …”

“…However, in the majority of examples reported so far, A′ and A′′ cations are the same (A′=A′′), and the intrinsic triple order is hidden, for example, in CaFeTi 2 O 6 , CaMnTi 2 O 6 , RMnMnSbO 6 (R=La, Pr, Nd and Sm), RMnGaTiO 6 (R=Sm and Gd), RMnMn 2 O 6 ≡RMn 3 O 6 (R=Gd‐Tm and Y), CaMnFeReO 6 and CaMnMnReO 6 , where short formula look like double perovskites. There is only one example where A′ and A′′ cations are different, Ca 2 CuMnFe 2 Re 2 O 12 , and this compound shows a partial ordering of Cu 2+ and Mn 2+ between the A′ and A′′ sites . There is also an example where the same cation (A′=A′′=Mn) has different oxidation states at the A′ and A′′ sites, [R 3+ 2 ] A [Mn 3+ ] A′ [Mn 2+ ] A′′ [Mn 3+ 2 ] B1 [Mn 3+ Mn 4+ ] B2 O 12 …”

“…Among A‐site‐ordered structures, the 1 : 3 body‐centered ordering of AA′ 3 B 4 O 12 quadruple perovskites is dominant ,,. There are possibilities of simultaneous ordering at the A and B sites as in the so‐called doubly ordered (or double double), perovskites AA′BB′O 6 and in AA′ 3 B 2 B′ 2 O 12 quadruple perovskites …”

“…The a + a + c − (1 : 1 : 2) tilt system results in the so‐called A‐site columnar‐ordered A 2 A′A′′B 4 O 12 quadruple perovskites with a ten‐fold coordinated A site, a square‐planar coordinated A′ site, and a tetrahedrally coordinated A′′ site (Figures and S1) . However, in the majority of examples reported so far, A′ and A′′ cations are the same (A′=A′′), and the intrinsic triple order is hidden, for example, in CaFeTi 2 O 6 , CaMnTi 2 O 6 , RMnMnSbO 6 (R=La, Pr, Nd and Sm), RMnGaTiO 6 (R=Sm and Gd), RMnMn 2 O 6 ≡RMn 3 O 6 (R=Gd‐Tm and Y), CaMnFeReO 6 and CaMnMnReO 6 , where short formula look like double perovskites. There is only one example where A′ and A′′ cations are different, Ca 2 CuMnFe 2 Re 2 O 12 , and this compound shows a partial ordering of Cu 2+ and Mn 2+ between the A′ and A′′ sites .…”

Rise of A-site columnar-ordered A2A′A′′B4O12 quadruple perovskites with intrinsic triple order

“…21 In the last few years, A 2 A′A″B 4 O 12 quadruple perovskites have experienced rapid growth. 18,[22][23][24] The purpose of this frontier article is to highlight their underinvestigated status and great potential and to attract attention of the perovskite and high-pressure communities. The A 2 A′A″ B 4 O 12 quadruple perovskites are compared with the AA′ 3 B 4 O 12 ones.…”