Research Center for Magnetic Materials and Devices, Key Laboratory for Advanced Functional and Low Dimensional Materials of Yunnan Higher Education Institute, Qujing Normal University, Qujing, 655011, China.
State Key Laboratory for Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
Sci Rep. 2017 Jan 30;7:41675. doi: 10.1038/srep41675.
We report a detailed study of two successive first-order transitions, including a martensitic transition (MT) and an antiferromagnetic (AFM)-ferromagnetic (FM)-like transition, in MnFeNiGe (x = 0, 0.06, 0.11) alloys by X-ray diffraction, differential scanning calorimetry, magnetization and linear thermal expansion measurements. Such an AFM-FM-like transition occurring in the martensitic state has seldom been observed in the M(T) curves. The results of Arrott plot and linear relationship of the critical temperature with M provide explicit evidence of its first-order magnetoelastic nature. On the other hand, their performances as magnetocaloric and negative thermal expansion materials were characterized. The isothermal entropy change for a field change of 30 kOe reaches an impressive value of -25.8 J/kg K at 203 K for x = 0.11 compared to the other two samples. It demonstrates that the magneto-responsive ability has been significantly promoted since an appropriate amount of Fe doping can break the local Ni-6Mn AFM configuration. Moreover, the Fe-doped samples reveal both the giant negative thermal expansion and near-zero thermal expansion for different temperature ranges. For instance, the average thermal expansion coefficient ā of x = 0.06 reaches -60.7 × 10/K over T = 231-338 K and 0.6 × 10/K over T = 175-231 K during cooling.
我们通过 X 射线衍射、差示扫描量热法、磁化和线性热膨胀测量，详细研究了 MnFeNiGe（x=0、0.06、0.11）合金中两个连续的一级相变，包括马氏体相变（MT）和反铁磁（AFM）-铁磁（FM）类似相变。在 M(T) 曲线中很少观察到在马氏体状态下发生的这种 AFM-FM 类似相变。Arrott 图和临界温度与 M 的线性关系的结果提供了其一级磁弹性质的明确证据。另一方面，我们还研究了它们作为磁热和负热膨胀材料的性能。对于 x=0.11 的样品，在 203 K 时，磁场变化 30 kOe 时的等温熵变化达到了令人印象深刻的值 -25.8 J/kg K，相比其他两个样品有显著提高。这表明适量的 Fe 掺杂可以打破局部 Ni-6Mn AFM 结构，从而显著提高了磁响应能力。此外，Fe 掺杂样品在不同温度范围内表现出巨大的负热膨胀和接近零的热膨胀。例如，x=0.06 的平均热膨胀系数 ā 在 T=231-338 K 范围内达到-60.7×10/K，在冷却过程中 T=175-231 K 范围内达到 0.6×10/K。
