Phase separation in a manganite La$_{0.95}$Ba$_{0.05}$MnO$_3$ crystal

The structure and magnetic states of a crystal of lightly doped manganite La$_{0.95}$Ba$_{0.05}$MnO$_3$ were studied using thermal-neutron diffraction, magnetic measurements, and electrical resistance data in a wide temperature range. It is shown that, in terms of its magnetic properties, the orthorhombic crystal is characterized by two order parameters, namely, antiferromagnetic ($T_N$ = 123.6 K) and ferromagnetic ($T_C$ = 136.7 K). The results obtained differ in detail from known information on the manganites La$_{0.95}$Ba$_{0.05}$MnO$_3$ and La$_{0.94}$Sr$_{0.06}$MnO$_3$. Two models of the magnetic state of the La$_{0.95}$Ba$_{0.05}$MnO$_3$ crystal are discussed, one of which is a model of a canted antiferromagnetic spin system and another is associated with the phase separation of the manganite. Arguments are advanced in favor of the coexistence in this crystal of the antiferromagnetic phase (about 87%) with a Mn$^{4+}$ ion concentration of 0.048 and the 1/16-type charge-ordered ferromagnetic phase (about 13%) with a Mn$^{4+}$ ion concentration of 0.0625. The specific features of the manganite studied are due to self-organization of the La$_{0.95}$Ba$_{0.05}$MnO$_3$ crystal lattice caused by the relatively large barium ion size.