Evidence of structural and two magnetic phase transitions in Cu doped La2FeMnO6 double perovskites

Abstract

In this report, we have addressed a comprehensive study on the structural phase transitions with the help of a combination of high temperature x-ray diffraction and temperature dependence Raman spectroscopy. We also report the magnetic ground state of all the samples at room temperature and 5 K. The combined high temperature x-ray diffraction and temperature dependence Raman study suggests that the samples undergo structural phase transitions from orthorhombic to tetragonal to cubic dominated mixed phase. With the help of x-ray photoelectron spectroscopy, we confirmed the presence of multi-oxidation states of Fe and Mn ions. The temperature evolution of magnetization data has been recorded at a field of 100 Oe and temperature range between 2 K and 300 K, and reveals the presence of two magnetic phase transitions for pristine, 10% and 20% doping of Cu in the composition La 2 FeMn 1−x Cu x O 6 . The magnetic study of all the samples reveal that the magnetic ground state of all the samples shows paramagnetic nature at room temperature, whereas at lower temperature all the samples are ferromagnetic except the highest doped sample which is purely paramagnetic. The law of approach to saturation method is imposed in the saturation region of M-H curve observed at 5 K. The transition temperature decreases with the amount of Cu doping, due to the substitution of Cu in Mn-site resulting in destroy of the Mn 3+ -O 2- - Mn 4+ bridges which is responsible for weakening of double exchange interaction between Mn 3+ and Mn 4+ . • Temperature dependent XRD has shown a structural phase transition from orthorhombic to tetragonal to cubic space group. • Temperature evolution of the phononic modes predominantly influenced by the lattice degrees of freedom. • Magnetic studies have shown two phase transitions confirming low temperature FM phase with different ordering mechanisms.