Jiachen Zhu

Co doping is an effective means to improve the performance of Ni–Mn–Sn alloy bulks and thin films. However, the Co doping effect on the crystallization process of the Ni–Mn–Sn alloy thin films is important but not clear. Therefore, we investigate the influence of Co doping on the crystallization kinetics for Ni₅₀Mn_37−xSn₁₃Co_x (x = 0, 0.5, 1.5, 4) magnetic shape memory alloy thin films by DSC analysis. For the non-isothermal process, each DSC curve has a single exothermic peak, which is asymmetrical. The crystallization peak temperatures and the activation energy of thin films both rise gradually with increasing Co content. Then, the activation energy of Ni₅₀Mn_37−xSn₁₃Co_x (x = 0, 0.5, 1.5, 4) thin films obtained by the Kissinger equation method is determined as 157.9 kJ mol⁻¹, 198.8 kJ mol⁻¹, 213 kJ mol⁻¹ and 253.6 kJ mol⁻¹, respectively. The local activation energy of thin films with different Co content show the different variation tendency. In the isothermal crystallization, the average of the Avrami exponent n for thin films of each Co content is approximately 1.5, suggesting that the mechanism of crystallization is two-dimensional diffusion-controlled growth for Ni₅₀Mn_37−xSn₁₃Co_x (x = 0, 0.5, 1.5, 4) thin films.

In this paper, polycrystalline Ni50−xCuxMn38Sn12 alloys (x = 0, 2, 4, 6) were prepared. The influence of Cu doping on the martensitic transformation and magnetic properties were investigated in these alloys. Experimental results indicate that the martensitic transformation temperature decreases and the Curie temperature increases with the increasing of substitution of Cu for Ni. Therefore, the magnetic properties in both austenitic and martensitic phases could be tuned by Cu content in these alloys. In addition, magnetoresistance were also performed and discussed in detail. A large magnetoresistance (up to 39%) was obtained by the magnetic field induced reverse martensitic transformation.