Structural properties, magnetic interactions, magnetocaloric effect and critical behaviour of cobalt doped La_0.7Te_0.3MnO₃

The effect of cobalt doping on the structural, magnetic and magnetocaloric properties of electron-doped manganite La_0.7Te_0.3Mn_1-xCo_xO₃ (x = 0, 0.1, 0.2, 0.25, 0.3 and 0.5) has been investigated. The parent compound La_0.7Te_0.3MnO₃ crystallizes in a rhombohedral structure with R3¯c space group. With the increase in Co concentration to x = 0.2, a structural transition from rhombohedral (R3¯c space group) to orthorhombic (Pbnm space group) is observed. X-ray photoelectron spectroscopy (XPS) indicates that the structural transition is due to the disordered distribution of Mn²⁺/Mn³⁺ and Co²⁺/Co³⁺ ions. All the samples undergo a paramagnetic-ferromagnetic (PM-FM) phase transition. With the increase in Co content to x = 0.1, the unit cell volume increases with a decrease in both Mn-O-Mn bond angle and T_c indicating a weakening of the double exchange interaction. However, with further increase in Co concentration, T_c increases. The presence of competing ferromagnetic and antiferromagnetic interactions leads to a glassy behaviour at low temperatures for low Co doping concentrations. However, for higher Co concentrations, no such behaviour is observed. Arrott plots reveal a second order nature of magnetic transition for all the samples. The magnetic exchange interactions for x = 0.3 and 0.5 follow the mean-field model. Magnetization results show that the magnetocaloric property of the electron-doped manganite is affected by the substitution of Co at Mn sites. Relatively large values of relative cooling power and broad temperature interval of the magnetocaloric effect make the present compounds promising for sub-room temperature magnetic refrigeration applications.