Structure, Magnetism, and Properties of Ruddlesden−Popper Calcium Manganates Prepared from Citrate Gels

Abstract

Ruddlesden-Popper (RP) phases with the formula (CaO)(CaMnO 3 ) n , where n ) 1, 2, 3, and ∞, have been prepared using the Pechini citrate gel process at temperatures as low as 900 °C under flowing oxygen. The compounds were characterized by X-ray powder diffraction, Rietveld profile analysis, thermal gravimetric analysis, iodometric titrations, Mn K-edge X-ray absorption spectroscopy, temperature-dependent magnetic susceptibility, and resistivity. Rietveld analysis shows that there is an elongation in the apical Mn-O distances of the MnO 6 octahedra, which increases with decreasing dimensionality. Mn K-edge X-ray absorption spectroscopy and iodometric titrations show no detectable amount of Mn 3+ (a Jahn-Teller distorted d 4 ion) in the samples indicating that the MnO 6 deformation may be associated with a splitting in the half-filled t 2g levels of Mn 4+ . Magnetic susceptibility measurements show spontaneous magnetic ordering to antiferromagnetic states at ∼125 K for CaMnO 3 and Ca 4 Mn 3 O 10 and at ∼110 K for Ca 2 MnO 4 and Ca 3 Mn 2 O 7 . The effective magnetic moment is greatly suppressed in all of the RP manganates, even in the threedimensional CaMnO 3 , n ) ∞ phase, and decreases dramatically with decreasing dimensionality. Large deviations from Curie-Weiss behavior are observed above the ordering temperature, which increase with decreasing n. These observations are discussed in terms of two-dimensional magnetic fluctuations and alternative mechanisms. The compounds are all poor electronic conductors with room-temperature resistivities in the range of 10 2 -10 4 Ω cm.

Synthesis and structural properties of n= 1 Ruddlesden–Popper manganites Nd1−Ca1+MnO4

“…8 the temperature dependence of the magnetization under a field of 0.5 T for x = 0.55, 0.67, 0.70, 0.75, 0.80 and 1.00. The sudden decrease toward lower temperatures around 110 K at x = 1.00 corresponds to an antiferromagnetic phase transition (T N ∼ = 110 K) [15], whereas the relatively gradual suppression at x = 0.67, 0.70 and 0.75 corresponds to the COO phase transition; we confirmed that the diffuse superlattice reflections appear around the temperatures indicated by the black arrows and the intensity increases progressively with decreasing temperature. It is well known that most of COO phases of manganites exhibit structural modulations based on the MnO 6 Jahn-Teller distortions and suppression of magnetization which is ascribed to the weakened double-exchange interaction due to locarization of the e g electrons.…”

Non-adiabatic small polaron hopping in then= 3 Ruddlesden–Popper compound Ca4Mn3O10

“…Activated conduction at high T has been reported for all undoped Ca n+1 Mn n O 3n+1 materials 23 , which, for n = 1, has been ascribed to small polaron hopping 24 .…”

Growth of Ca2MnO4 Ruddlesden-Popper structured thin films using combinatorial substrate epitaxy

“…For example, the layered cuprate RP phases played important roles in the discovery of hightemperature superconductivity, [3][4][5][6] and the manganese-based RP family displays insulator-to-metal and ferromagnetic transformations at low temperatures, yielding colossal magnetoresistive properties. 3,10,[13][14][15][22][23][24] The structural, transport, and magnetic properties of nickelate RP compounds have also been extensively investigated, 12,25 being of recent interest as cathode materials in solid oxide fuel cells (SOFCs). 17 Other exotic properties include p-wave superconductivity in the RP ruthenate Sr 2 RuO 4 , 16 novel insulating electronic ground states from spin-orbit-coupling in Sr 2 IrO 4 , 20,26 and noncentrosymmetry in Ca 2 IrO 4 .…”