The martensitic transformation sequence in two single crystalline Ni-Mn-Ga alloys with a martensite start temperature ${(M}_s)$ of about 400 K has been investigated using dynamic mechanical analysis, calorimetry, dilatometry, three-point bending tests, and transmission electron microscopy. A two-step thermally induced martensitic transformation during cooling and one-step reverse transformation during heating have been found in both alloys, although involving different modulated martensitic phases in each of the alloys. In one of them, the first martensitic transformation leads to a martensitic phase having a commensurate modulated lattice characterized by a periodic stacking sequence of ten $\{110{\}}_P$ planes along the $〈110{〉}_P$ direction. On further cooling, a second transformation to a modulated martensite with a periodicity of seven planes has been observed. In the other alloy, the transformation sequence observed on cooling is from the parent phase to an eight-layered modulated martensite followed by a second transformation to a martensite having a tetragonal lattice $\mathrm{}(c/a>\mathrm{}1\mathrm{})\mathrm{}$ without modulation.

Magnetomechanical experiments were performed with a ferromagnetic Ni–Mn–Ga single crystal consisting of thermoelastic orthorhombic martensitic phase at room temperature. The crystal was deformed in uniaxial compression along 〈100〉 with an orthogonal magnetic field and without a magnetic field. The sample deforms due to motion of twin boundaries. When compressed with a magnetic field, twinning occurs at higher stress than without a magnetic field, and the twinning is reversible upon unloading. The stress–strain curves exhibit two plateaus which are related to two different twinning systems, namely $\text{(110)[11̄0]}$ and $\text{(011)[011̄].}$ During cyclic experiments in a rotating magnetic field, the magnetic-field-induced strain increases from initially 6% to 9.7%. The latter value was repeatedly measured upon more than 1000 rotations of the field. The increase of magnetic-field-induced strain during magnetomechanical cycling is related to a transition from combined partial $\text{(110)[11̄0]}$ and $\text{(011)[011̄]}$ twinning to complete $\text{(101)[101̄]}$ twinning. The magnetic anisotropy constants are obtained from an analysis of the magnetomechanical properties.