Ni-Mn-X (X=In, Sn and Sb) ferromagnetic shape memory alloys (FSMAs) have attracted significant attention due to their interesting physical properties, such as large magnetic-field-induced strain, giant magnetocaloric effects (MCEs), large magnetoresistance (MR), and exchange bias (EB) These properties make them promising for various practical applications in the field of smart, magnetic refrigeration materials and spintronics [1] In these alloy systems, the martensitic transformation (MT) coincides with the magnetic transformation from a cubic L21 structure ferromagnetic (FM) austenite to an orthorhombic weak-magnetic martensite It is reported that the martensitic transformation temperature (TM) of FSMAs can be tuned by altering the composition of the alloys or substituting elements, and is very sensitive to the values of the valence electron concentration e/a (electrons per atom) [2] In stoichiometric Ni2MnSn alloy, no martensitic transition is observed However, Mn-rich Ni50Mn25+xSn25x compounds, in which the excess Mn atoms occupy the vacant Sn (4b) sites, exhibit the martensitic transition from high-symmetry austenitic phase to a low symmetry martensitic phase [2] Up to 2007, large inverse MCE has been found in Ni0.50Mn0.50-xSnx (0 13 ≤ × ≤ 0.15) alloys, in which the magnetization difference (ΔM) from martensitic to austenite about 20 emu/g is observed, with the applied eld of 10 kOe [3] In addition, rapid solidication by melt-spinning process offers a metallurgically interesting route to synthesizing ribbons with highly textured microstructure The melt-spinning technique has been employed to synthesize Ni-Mn-Sn materials with improved magnetocaloric properties In order to elevate TM and enhance saturation magnetization of austenite phase, the Co substitution for Mn in Mn49Ni41Sn10 alloy might be an effectively way due to its e/a value is increased by Co doping Therefore, in this work, Mn49-xCox Ni41Sn10 (x=0−4) alloy ribbons were obtained using melt-spinning technique at a wheel speed of 20 m/s The as-spun ribbons were annealed at 1073 K for 10 min and nally quenched in ice water The effects of Co substitution for Mn on phase transformations and MCE of these ribbons were measured by vibrating sample magnetometer Fig 1 shows the temperature dependence of magnetization of Mn49-xCoxNi41Sn10 (x=0−4) ribbons in a magnetic eld of 1 kOe on heating in the temperature range between 150 and 350 K The ferromagnetic behavior of austenite is improved with increasing Co content originated from the enhancement of ferromagnetic exchange interaction As a result, the magnetization difference (ΔM) from martensitic to austenite is also enhanced. In addition, the TM also increases from 139 7 K to 251 6 K with increasing Co content from x = 0 to x = 4 This phenomenon can be attributed to the increased e/a value by Co-doping The temperature dependence of calculated ΔSM in the vicinity of TM under magnetic eld of 10 kOe is shown in Fig 2 An average ΔSMmax value of 12 5 J/kgK is easily obtained in different operation temperature region.