Structural, magnetic phase transitions and magnetocaloric effect in Sm_1-xR_xMn₂Ge₂

Full text: Rare earth-based intermetallic compounds attract special attention due to their potential for various applications. One important application is as magnetocaloric materials essential for magnetic refrigeration. The SmMn₂Ge₂ compound usually forms in the ThCr₂Si₂ structure (space group I4/mmm) with the layered nature of this crystal structure leading to strong dependence of the magnetic interactions on the interplanar and intraplanar interatomic Mn-Mn distances. There is potential in this system for enhancement of the magnetocaloric effect (MCE) because the layered nature allows the control of the intrinsic magnetism via inter and intraplanar separations of the Mn and Sm atoms in turn controlling the large magnetisation due to ferromagnetic coupling between the Mn and Sm sublattices below the Sm ordering temperature. In this report, the influence of substitution of other heavy rare earths (R = Dy, Ho and Er) for Sm in terms of magnetism, lattice parameter, and MCE are discussed. The structural properties of the Sm_1-xR_xMn₂Ge₂ series compounds have been investigated in detail using Xray diffraction, both laboratory and synchrotron measurements over the temperature range 12 to 450 K. While magnetic properties were explored via magnetic susceptibility in the range 0 to 310 K and differential scanning calorimetry (DSC). The MCE effect has also been quantified with magnetisation isotherms recorded to a maximum field of 5.0 T from which magnetic entropy changes are derived. (author)