Structures and physical properties of la_xCa_4-xMn ₃O₁₀ (x= 0, 0.1) synthesized under high pressure

The nominal composition compounds La_xCa_4-xMn ₃O₁₀, (x=0, 0.1) were synthesized using solid-state reaction under high pressure. The structures of the two samples have been studied by x-ray powder diffraction, transmission electron microscopy, and high-resolution electron microscopy. In the case of the nominal composition La_0.1Ca_3.9Mn₃O₁₀, besides the phase with n =2 member of Ruddlesden-Popper (RP) series, the phase with the ideal n=3 member RP structure (space group I4/mmm) was formed. Moreover, it is interesting that some intergrowth or modulation structures were observed in some areas of n=3 phase. Based on the analysis of magnetic and electrical properties, La _xCa_4-xMn₃O₁₀ undergoes from a paramagnetic-antiferromagnetic transition (x=0) at 104 K to paramagnetic-weak ferromagnetic transition (x=0.1) at 113 K ascribed to existence of La doped n=3 phase La_xCa._4-xMn₃O₁₀ and intergrowth or modulation structures. Similar conductive mechanism, two-dimensional variable range hopping, is shown above magnetic transition temperatures for both samples. Compared to the very weak magnetoresistance in Ca₄Mn₃O₁₀, the nominal composition La _0.1Ca_3.9Mn₃O₁₀ represents a 65% drop in resistivity in a magnetic field of 5 T at 5 K.