Abstract

When applying a magnetic field parallel or perpendicular to the long edge of a parallelepiped Ni-Mn-Ga stick, twin boundaries move instantaneously or gradullay through the sample. We evaluate the sample shape dependence on twin boundary motion with a micromagnetics computational study of magnetic domain structures and their energies. Due to the sample shape, the demagnetization factor varies with the direction of external magnetic field. When the external magnetic field is applied perpendicular to the long edge of the sample, i.e. in the direction in which the demagnetizing field is highest, the magnetic energy intermittently increases when the strength 2 of the applied magnetic field is low. This energy gain hinders the twin boundary motion and results in a gradual switching, i.e. a gradual magnetization reversal as the applied magnetic field is increased. The formation of 180⁰ magnetic domains offsets this effect partially. In contrast, when the applied magnetic field is parallel to the long edge of the sample, i.e. in the direction in which the demagnetizing field is lowest, the energy decreases with each subsequent magnetization domain reversal and the twin boundary moves instantaneously with ongoing switching. The actuation mode with the field parallel to the long sample edge lends itself for on-off actuators whereas the actuation mode with the field perpendicular to the long sample edge lends itself to gradual positioning devices.

Thermal and magnetic properties of a recently developed metallic glass of four different compositions [{Co (1Àx) Fe (x) } (0.75) B (0.2) Si (0.05) ] 96 Cr 4 were evaluated, where x = 0, 0.1, 0.2, and 0.3. Coercivity decreased and saturation magnetization increased with the increase in iron content. All alloys showed a high Curie temperature. The trend in thermal stability and magnetic properties was explained by atomic interactions between the constituent elements and s-d hybridization between the ferromagnetic metal and the metalloid atoms.Low hysteresis losses, high saturation magnetization, and low coercivity make Co-Fe based soft magnetic alloys attractive for a number of applications including transformers, motors, sensors, magnetometers, and data recording. [1,2] Magnetic properties of several Co-Fe based nanocrystalline alloys have been investigated for low-loss applications. [3] However, nanocrystalline alloys have grain boundaries, crystalline defects, and different crystal orientations, which limit their use in magnetic applications. In contrast, metallic glasses are free of grain boundaries and have a homogeneous structure, which are potential advantages for developing low-loss soft magnetic materials with controlled properties. High glass transition temperature (T g ) and high Curie point of Co-Fe based metallic glasses are added advantages for high temperature soft magnetic applications. The high Curie point of Co-Fe alloys stems from the strong exchange interaction of magnetic spin between Co and Fe atoms. [4] Therefore, optimum addition of Fe to Cobased metallic glasses may result in enhancement of magnetic properties as well as glass forming ability (GFA).High permeability, [5] excellent mechanical properties, low magnetostriction, and low coercivity are some desirable properties reported for Co-Fe metallic glasses. [6][7][8] The saturation magnetization value for Co-Fe-Ta-B system has been reported to be around 0.5 T with 0.25-0.9 A/m coercivity. Along with good thermal stability, this alloy system exhibits excellent mechanical properties, such as high fracture strength of 5185 MPa. [7,9] Inoue et al. reported the magnetic properties of Co-Fe-Si-B-Nb system with saturation magnetization around 0.60 T and coercivity of 1.55 A/m. [10] Recently, the effect of Cu and Tb (non-magnetic elements) addition on the glass formability and magnetic properties of iron-based metallic glasses has been studied. Addition of Cu and Tb resulted in lowering of glass formability and enhancement of soft magnetic properties. [11,12] However, the change in magnetic properties by systematically changing the iron content in Co-based soft magnetic metallic glasses has not been investigated till date. Furthermore, there are no reports on the magnetization behavior at high temperatures for Co-Fe metallic glasses. Systematic investigation of GFA and magnetic properties for Co-Fe metallic glasses can lead to valuable scientific insight and novel engineering applications.In the present work, the effect of iron content on the gl...

An in situ composite coating on pure aluminium substrate was prepared by novel microwave processing of iron based metallic glass powder precursor. The microstructure obtained after processing comprised of a molybdenum rich harder phase uniformly distributed in iron rich softer phase. The hardness and modulus of each phase were obtained by nanoindentation. Scratch test across the substrate coating indicated good interface strength and strong adhesion of the coating with the substrate.