Primary Sensory and Motor Cortex Activities During Voluntary and Passive Ankle Mobilization by the SHADE Orthosis

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Martensitic Transformation in Ni-Mn-Ga Thin Films Deposited on Alumina

Ni-Mn-Ga magnetic shape memory alloys (MSMAs) tend to undergo a large, reversible deformation upon the application of a magnetic field. This deformation is attributed to twin boundary motion in the martensitic phase. In an effort to utilize the magneto-mechanical behavior of Ni-Mn-Ga polycrystalline thin films for micro-sensors and actuators, the behavior of Ni- Mn-Ga thin films is paid a great attention last few years. Substrate curvature measurements on Ni-Mn-Ga films, deposited on Al2O3 ceramics, were performed. The martensitic transformation in the film is manifested by an anomalous stress change accompanied by thermal hysteresis. The stress-curvature experiments display a stress relaxation during the martensitic transformation of approximately 30–100 MPa, depending on film thickness

Magnetic Anisotropy, Stress, and Martensitic Transformation in Ni-Mn-Ga Thin Films on Si(100) Wafer

Ni-Mn-Ga magnetic shape memory alloys (MSMAs) tend to undergo a large deformation upon the application of a magnetic field. This deformation is attributed to twin boundary motion in the martensitic phase. In an effort to harness the shape memory effect for use in sensors, actuators, and micro-devices, the behavior of Ni-Mn-Ga thin films is attracting attention. Substrate curvature measurements were done with Ni-Mn-Ga films with a thickness of 2.0 μm sputter-deposited on Si(100) wafer having amorphous 500 nm thick SiNx buffer layer. During the wafer bow curvature measurements, stress levels of 0.65 GPa were attained. The martensitic transformation is manifested by a stress-temperature hysteretic loop. Measurements of magnetization curves were carried out on Ni-Mn-Ga films with thickness between 0.5 and 3.0 μm. A change of the magnetization behavior from the easy-plane type for thin films to the out-of-plane easy-axis type for thick films is observed. This effect is caused by the interplay between different contributions to the overall anisotropy of film

Ferromagnetic Shape Memory Materials: Underlying Physics and Practical Importance

The underlying physics of the giant magnetic or mechanical field-induced-strains in Ni–Mn–Ga alloys are briefly discussed. For the purpose of illustrating some fundamental aspects, experimental data relative to lattice instability and composition dependence of magnetization are presented alongside reported results. An implementation of Ni–Mn–Ga single crystal as a strain sensor is described

Properties of Sputter-Deposited Ni–Mn–Ga Thin Films

Sub-micrometer Ni–Mn–Ga films on MgO(0 0 1) single-crystalline wafers have been prepared by radio-frequency magnetron sputtering. The structural and magnetic states of the as-received (quasi-amorphous phase) and annealed (highly ordered martensitic phase at T = 300 K) films have been examined by X-ray diffraction, and measurements of resistivity and magnetization. The annealed films demonstrate a transformation behavior typical for the bulk and show a thickness dependence of the magnetic properties

Incommensurate and Commensurate Structural Modulation in Martensitic Phases of FSMA

Magnetic and structural properties in multifunctional FSMA (Ferromagnetic Shape Memory Alloys) belonging to Heusler family are frequently related to the occurrence of structural modulation in martensitic phases. The highest MFIS (Magnetic Field Induced Strain) effect has been observed in Ni-Mn-Ga alloys showing martensitic modulated structures. Depending on the composition, pressure and temperature conditions, this periodic structural distortion, consisting of shuffling of atomic layers along specific crystallographic directions, accompanies the martensitic transformation. Over the years, different modulated martensitic structures have been observed and classified depending upon the periodicity of corresponding superstructure (nM with n=3, 5, 6, 7, 12 etc). On the other hand, it has been demonstrated that in most cases such structural modulation is incommensurate and the crystal structure can be solved by applying superspace approach. The crystallographic representation of different modulated structures, obtained by structure refinement on powder diffraction data, suggests a unified description where every different “nM” periodicity can be straightforwardly represented. It will be presented an overview illustrating structural features of several displacive modulated martensitic lattices. For a specific Ni-Mn-Ga composition, the evolution of structural modulation upon temperature change will be illustrated

Magnetic Susceptibility of Martensitic Ni–Mn–Ga Film

The present work deals with the magnetic anisotropy of a textured Ni51.4Mn28.3Ga20.3 thin film sputter deposited on alumina ceramic substrate. This film is a ferromagnetic martensite with a strong uniaxial magnetocrystalline anisotropy. The magnetization versus magnetic field dependencies at different angles between the direction of magnetic field and the film plane are measured with a vibrating sample magnetometer. The initial magnetic susceptibility decreases with increasing inclination with respect to the film plane. A consistent procedure is introduced for the quantitative determination of (i) the angle of the easy-magnetic axis with respect to the film normal and (ii) the ratio between the magnetic anisotropy energy and the magnetostatic energy (quality factor). These values proved to be equal to 67°±4° and 2.9±0.3, respectively