Modulated structure of Ni–Mn–Ga-based alloys is decisive in their magnetic shape memory (MSM) functionality. However, the precise nature of their five-layered modulated 10M martensite is still an open question. We used x-ray and neutron diffraction experiments on single crystals to investigate structural changes within 10M-modulated martensite of the Ni₅₀Mn₂₇Ga₂₂Fe₁ MSM alloy. The modulation vector gradually increases upon cooling from commensurate q = (2/5) g ₁₁₀, where g ₁₁₀ is the reciprocal lattice vector, to incommensurate with q up to pseudo-commensurate q = (3/7) g ₁₁₀. Upon heating, reverse changes are observed with a thermal hysteresis of ≈60K. The same hysteretic behaviour was detected in the electrical resistivity and the effective elastic modulus. Scanning electron microscopy showed that the changes are accompanied by the refinement of the a/b laminate. These observations indicate that the commensurate state is a metastable form of 10M martensite. Upon cooling, this phase evolves through nanotwinning into a more irregular and more stable incommensurate structure.

Ni-Mn-Ga 基合金的调制结构对其磁性形状记忆 (MSM) 功能具有决定性意义。然而，他们的五层调制 10M 马氏体的确切性质仍然是一个悬而未决的问题。我们在单晶上使用 X 射线和中子衍射实验来研究 Ni ₅₀ Mn ₂₇ Ga ₂₂ Fe ₁ MSM 合金的10M 调制马氏体内的结构变化。调制矢量在冷却时逐渐增加，从相称q = (2/5) g ₁₁₀，其中g ₁₁₀是倒易晶格矢量，与q不相称，直至伪相称q = (3/7)克 ₁₁₀。加热时，观察到反向变化，热滞后约为 60K。在电阻率和有效弹性模量中检测到相同的滞后行为。扫描电子显微镜显示，这些变化伴随着a / b层压板的细化。这些观察表明，相称状态是 10M 马氏体的亚稳态形式。冷却后，该相通过纳米孪晶演变成更不规则和更稳定的非公度结构。