Ball milling effect on structural and magnetic properties of Ni–Mn–Ga ferromagnetic nanoparticles

Abstract

The off-stoichiometric Ni 2 MnGa ferromagnetic alloys are one of the active materials that are of great interest when they are ball milled into nanopowder. These powders are prospective materials for nanosystem applications. However, the properties of the nanocrystalline Ni-Mn-Ga alloys depend strongly on their structure and internal stress, which develop during the milling process.Ni-Mn-Ga nanoparticles were prepared by ball-milling method, and characterized by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) techniques. The powders are found to be a disordered mixture structure of austenite and martensite. We calculated that an average internal stress is 0.28 to 2.05 MPa stored in the distorted lattice due to milling. Reduction in particle sizes is accompanied by increase of the lattice strain level when the milling time increases. The VSM reveals that magnetic saturation and coercivity decrease with increase of the milling duration. This phenomenon causes deterioration in the hard magnetic properties.

Structure and magnetic properties of Ni–Mn–Ga shape memory alloys

“…Shape memory alloys (SMAs) are alloys that can restore the original shape under influence of temperature or an external magnetic field. The origin of the shape memory effect (SME) is due to the transformation of the crystal structure of the material when temperature or magnetic field acts on it [1][2][3][4][5][6][7][8][9][10][11]. The SMAs can exist in two different crystalline phases including the martensitic phase (stable at low temperature) and austenitic phase (stable at higher temperatures) [1][2][3][4][5][6][7][8][9].…”

“…The origin of the shape memory effect (SME) is due to the transformation of the crystal structure of the material when temperature or magnetic field acts on it [1][2][3][4][5][6][7][8][9][10][11]. The SMAs can exist in two different crystalline phases including the martensitic phase (stable at low temperature) and austenitic phase (stable at higher temperatures) [1][2][3][4][5][6][7][8][9]. The SMAs are capable of many applications in the fields of biomedicine, aerospace, microelectronics, automation: orthodontics, stents, bone anchors, automatic valves, heat sensors, nanotweezers, robots, etc.…”

“…Nowadays, one of the SMAs that increasingly attract interest in research is Ni-Mn-Ga Heusler alloy because of their application in the field of actuators and sensors [1][2][3][4][5][6][7][8]. These alloys have giant magnetic-field-induced strains which allow their use as magnetic actuators, and fast response by application of a magnetic field [12][13][14][15][16][17][18][19][20].…”