Crystal Structure and Magnetic Properties in B-Site-Disordered La1.75Ca0.25MnMO6 (with M = Ti and Fe) Double Perovskites

Double perovskite La1.75Ca0.25MnMO6 (with M = Ti and Fe) systems were elaborated employing a solid-state reaction method. The refinement of X-ray diffraction patterns shows that La1.75Ca0.25MnFeO6 (LCMFO) and La1.75Ca0.25MnTiO6 (LCMTO) compounds crystallize in an orthorhombic structure with the Pbnm space group. The electron density plots indicated the covalent nature between Mn/Ti/Fe and oxygen ions. The results of the temperature dependence of the magnetization show that these samples present a paramagnetic-antiferromagnetic transition at 230 K and 223 K for LCMFO and LCMTO, respectively. The non-null magnetization and magnetic hysteresis loop at room temperature can indicate the formation of weak ferromagnetism in the paramagnetic (PM) region in both compounds. Moreover, our magnetic results show a complex magnetic response in these materials below TN, which can be attributed to the formation of various types of magnetic exchange interactions within the system such as antiferromagnetic (AFM), (ferromagnetic) FM, and ferrimagnetic (FiM) couplings. Consequently, exchange coupling between the FM and/or FiM moments and AFM antiphase boundaries is responsible for the observation of exchange bias in the materials. Considering practical applications of perovskites, the present observation of the exchange bias effect and room temperature ferromagnetism in these materials may have great technological importance.