Ga含量对Mn2-xNiGa1+x结构和磁性的影响

系统研究了铁磁性形状记忆合金Mn_{2 -x}NiGa_1+x的结构、磁性和有序化转变. 研究表明: 随着Ga含量的增加, Mn_{2 -x}NiGa_1+x的母相结构由Hg₂CuTi 型逐渐转变到Cu₂MnAl型Heusler结构. 母相的晶格常数先增加后降低, 当x=0.3时达到最大值. 0.3 ≤x ≤0.8时, 材料除呈现Heusler结构的主相之外, 还出现了Ni₂In型六角相. 过渡金属中3d电子之间交换相互作用的减弱, 导致Mn_2-xNiGa_1+x主相的居里温度由Mn₂NiGa的590 K逐渐降低至Ga₂MnNi的220 K左右; 当x=0.6–0.8时, Ni₂In型六角相的居里温度与主相的居里温度出现分离. Ga对Mn的替代引起合金中原子间耦合作用的变化, 导致低温下Mn_{2 -x}NiGa_1+x的饱和磁化强度先增加后降低, 即x≤0.4时呈上升趋势, x>0.4时急剧下降. 差热分析结果显示, 随着x从0增加到1, 样品熔化温度逐渐降低, B2相到Heusler相的转变温度先降低后增加.

Influences of Ga content on the structure and magnetic properties of Mn2 -xNiGa1+x alloys

The structure magnetism and ordering transition of the ferromagnetic shape memory alloy Mn_{2 -x}NiGa_1+xhave been systematically studied in this paper. With increasing Ga content, the structure of the parent phase Mn_{2 -x}NiGa_1+x is transformed from Hg₂CuTi-type to Cu₂MnAl-type Heusler alloy gradually. Its lattice constant increases first and then decreases, reaching its maximum at x=0.3. The sample displays both the primary phase of Heusler and the Ni₂In-type hexagonal phase in precipitate form when x lies in the range of 0.3-0.8. The Curie temperature of the primary phase of Heusler alloy Mn_{2 -x}NiGa_1+x reduces gradually from 590 K for Mn₂NiGa to about 220 K for Ga₂MnNi with the decrease of the exchange interaction between 3d electrons in the transition metals. However, the variation of Curie temperature of Ni₂In-type hexagonal phase is gentle. The separation of Curie temperatures between the Ni₂In-type hexagonal phase and the primary phase of Heusler occurs when x lies in the range from 0.6 to 0.8. Substitution of Mn by Ga has a significant influence on the coupling interaction among various atoms, leading to first increasing and then decreasing of the saturated magnetization of Mn_{2 -x}NiGa_1+x at low temperatures. That is, the saturated magnetization will rise for x≤0.4 and drops sharply for x>0.4. Results of differential scanning calorimeter show that the melting temperature decreases gradually as x increases. Meanwhile, the transition temperature from parent phase (B2) to Heusler phase decreases first and increases later.