Crystal and magnetic structural study of the La1-xCaxMnO3 compound (x=3/4) -: art. no. 064426

We studied the crystal and magnetic structure of the La1/4Ca3/4MnO3 compound using ultrahigh resolution synchrotron x-ray and neutron-diffraction techniques. The experimental results revealed that the particular compound undergoes a structural transition at T-CO=220 K. This transition results in an increase of the orthorhombic splitting and the appearance of superlattice diffraction peaks, which can be indexed assuming a supercell 4a (a is the unit cell parameter for T > T-CO). This transition is reminiscent of those observed for the x=1/2 and x=2/3 stoichiometries where superstructures with 2a and 3a, respectively, have been observed. At T-N=160 K the neutron-diffraction patterns exhibit additional diffraction peaks, corresponding to antiferromagnetic long-range order with propagation vectors k=[1/4,0,1/2] and k=[1/2,0,1/2]. In addition to the structural transition at T-CO the synchrotron high resolution x-ray diffraction patterns revealed a three phase coexistence.