N. Lanska

Bio: N. Lanska is an academic researcher from Helsinki University of Technology. The author has contributed to research in topics: Crystal twinning & Magnetic shape-memory alloy. The author has an hindex of 17, co-authored 21 publications receiving 2578 citations.

Giant magnetic-field-induced strain in NiMnGa seven-layered martensitic phase

Abstract: Giant magnetic-field-induced strain of about 9.5% was observed at ambient temperature in a magnetic field of less than 1 T in NiMnGa orthorhombic seven-layered martensitic phase. The strain proved to be caused by magnetic-field-controlled twin boundary motion. According to an analysis of x-ray diffraction data, the crystal structure of this phase is nearly orthorhombic, having lattice parameters a=0.619 nm, b=0.580 nm, and c=0.553 nm (in cubic parent phase coordinates) at ambient temperature. Seven-layer shuffling-type modulation along the (110)[110]p system was recorded. The results of mechanical tests and magnetic anisotropy property measurements are also reported.

12% magnetic field-induced strain in Ni-Mn-Ga-based non-modulated martensite

Abstract: Magnetic field-induced strain (MFIS) of 12% is reported in ferromagnetic Ni 46Mn24Ga22Co4 Cu 4 martensite exhibiting non-modulated (NM) tetragonal crystal structure with lattice parameter ratio c / a > 1 . The strain was measured at ambient temperature in a magnetic field of the order of 1 T. The twinning stress σ T W and the magnetic stress σ M A G were also measured and the condition for a giant MFIS observation σ T W < σ M A G was confirmed. The MFIS was achieved in NM Ni 46Mn24Ga22Co4 Cu 4 martensite by considerable lowering of the σ T W value as compared to the values for NM martensites in ternary Ni-Mn-Ga system.

Twin microstructure dependent mechanical response in Ni–Mn–Ga single crystals

Abstract: Ni–Mn–Ga single crystals with a twinning stress of about 0.1 MPa were studied. They showed a tendency to stay in a single variant state and to retain only one or very few twin boundaries during martensite reorientation induced by an external stress or magnetic field. This makes the crystals problematic for application in a magnetic actuator. To solve the issue, we introduced many parallel twin boundaries into the crystals by bending. However, this twin microstructure was not stable under cycling load. Additionally, it exhibited a twinning stress of 0.8 MPa—about ten times higher than a crystal with a single boundary.

Temperature dependence of magnetic anisotropy in Ni–Mn–Ga alloys exhibiting giant field-induced strain

Abstract: Temperature dependence of structure and magnetic anisotropy of single crystalline Ni48.8Mn28.6Ga22.6 alloy exhibiting giant field-induced strain or magnetic shape memory (MSM) effect was studied in the temperature range 80–420 K. Upon cooling the alloy transforms from cubic austenite at 307 K to the martensite which exhibits five-layered (modulated) tetragonal structure (5M) with a=0.595 nm and c=0.559 nm. Reverse transformation occurs at 317 K. An additional intermartensitic transition takes place at about 95 K. The basic mechanism of the MSM effect was corroborated by direct simultaneous measurements of strain and magnetization as a function of magnetic field. The magnetic anisotropy of the martensite exhibiting the giant strain was determined from the magnetization curves measured by a vibrating sample magnetometer at different temperatures. The anisotropy of the single variant 5M martensite is uniaxial with easy axis along the tetragonal c axis. The first magnetic anisotropy constant is Ku1=2.0×105 J/...

Magnetic-field-induced shape recovery by reverse phase transformation.

Abstract: Large magnetic-field-induced strains1 have been observed in Heusler alloys with a body-centred cubic ordered structure and have been explained by the rearrangement of martensite structural variants due to an external magnetic field1,2,3. These materials have attracted considerable attention as potential magnetic actuator materials. Here we report the magnetic-field-induced shape recovery of a compressively deformed NiCoMnIn alloy. Stresses of over 100 MPa are generated in the material on the application of a magnetic field of 70 kOe; such stress levels are approximately 50 times larger than that generated in a previous ferromagnetic shape-memory alloy4. We observed 3 per cent deformation and almost full recovery of the original shape of the alloy. We attribute this deformation behaviour to a reverse transformation from the antiferromagnetic (or paramagnetic) martensitic to the ferromagnetic parent phase at 298 K in the Ni45Co5Mn36.7In13.3 single crystal.

Artificial muscle technology: physical principles and naval prospects

Abstract: The increasing understanding of the advantages offered by fish and insect-like locomotion is creating a demand for muscle-like materials capable of mimicking nature's mechanisms. Actuator materials that employ voltage, field, light, or temperature driven dimensional changes to produce forces and displacements are suggesting new approaches to propulsion and maneuverability. Fundamental properties of these new materials are presented, and examples of potential undersea applications are examined in order to assist those involved in device design and in actuator research to evaluate the current status and the developing potential of these artificial muscle technologies. Technologies described are based on newly explored materials developed over the past decade, and also on older materials whose properties are not widely known. The materials are dielectric elastomers, ferroelectric polymers, liquid crystal elastomers, thermal and ferroelectric shape memory alloys, ionic polymer/metal composites, conducting polymers, and carbon nanotubes. Relative merits and challenges associated with the artificial muscle technologies are elucidated in two case studies. A summary table provides a quick guide to all technologies that are discussed.

Magnetocaloric effect and its relation to shape-memory properties in ferromagnetic Heusler alloys

Abstract: Magnetic Heusler alloys which undergo a martensitic transition display interesting functional properties. In the present review, we survey the magnetocaloric effects of Ni-Mn-based Heusler alloys and discuss their relation with the magnetic shape-memory and magnetic superelasticity reported in these materials. We show that all these effects are a consequence of a strong coupling between structure and magnetism which enables a magnetic field to rearrange martensitic variants as well as to provide the possibility to induce the martensitic transition. These two features are respectively controlled by the magnetic anisotropy of the martensitic phase and by the difference in magnetic moments between the structural phases. The relevance of each of these contributions to the magnetocaloric properties is analysed.

Ferromagnetism in the austenitic and martensitic states of Ni-Mn-In alloys

Abstract: The magnetic and structural transformations in the Heusler-based system ${\mathrm{Ni}}_{0.50}{\mathrm{Mn}}_{0.50\ensuremath{-}x}{\mathrm{In}}_{x}$ are studied in the composition range $0.05\ensuremath{\leqslant}x\ensuremath{\leqslant}0.25$. While the cubic phase is preserved in the range $0.165\ensuremath{\leqslant}x\ensuremath{\leqslant}0.25$, we find the presence of martensitic transformations in alloys with $x\ensuremath{\leqslant}0.16$. In a critical composition range $0.15\ensuremath{\leqslant}x\ensuremath{\leqslant}0.16$, the magnetic coupling in both austenitic and martensitic states is ferromagnetic. Magnetic field-induced structural transitions are also found in the $x=0.16$ alloy, whereby the structural transition temperature shifts by $42\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in a field of $50\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$.