Abstract: The invention provides the use of a material of general formula (I): [(AyCo1-y)]u(Mn1-zCz)[(Si1-xBx)]v??(I) as a magnetocaloric material, wherein the material is orthorhombic and wherein: A is selected from Ni, Cr, Fe, Al, P, Se, Ga and Sb and mixtures thereof; B is selected from Ge, Sn, Al, P, Se, Ga and Sb and mixtures thereof; C is selected from Ni, Cr, Fe, Al, P, Se, Ga and Sb and mixtures thereof; x, y and z are the same or different and are numbers in the range 0 to 0.2; and u and v are the same or different and are numbers in the range 0.5 to 1.5. The invention also provides a method of making materials of formula (I) and a magnetocaloric refrigeration device comprising such materials.