Magnetic structure and magnetocaloric properties of LaMn₂Ge₂

Full text: The extensive set of ternary intermetallic RMn2X2 compounds (R = rare earth, T = transitional metal, X = Ge or Si) have been investigated extensively in the past few decades due to their interesting range of physical properties. Recently, significant attention has been paid to the magnetocaloric effect (MCE) of RMn2X2 compounds for their potential application in magnetic refrigeration. Their MCE properties are important as RMn2X2 compounds enable a wide range of structural and magnetic behaviours and related transitions to be controlled via substitution of R, Mn, and X atoms on the 2a, 4d, and 4e sites respectively. We have carried out a detailed investigation of the LaMn₂Ge₂compound using neutron diffraction and magnetic measurements, focusing on the magnetic behaviour of the Mn-sublattice. With decreasing temperature, the magnetic state changes from paramagnetism to incommensurate canted antiferromagnetism AFfs at TN ~ 360 K and then gives way to incommensurate canted ferromagnetism Fmi below TC ~ 323 K. No obvious magnetoelastic coupling were detected from refinement of the variable neutron diffraction patterns (5 K - 450 K) while detailed analyses of magnetic data indicate that the magnetic phase transition is second order. Under magnetic field changes of 2 T and 8 T, the maximum values of the magnetic entropy change (-DELTASM max) around TC reach 1.65 J/kg K and 4.42 J/kg K, respectively. (author)