Anomalous magnetizations in melt spinning Ni–Mn–Ga

Abstract

The structural and magnetic characteristics were studied for martensitic and austenitic Ni-Mn-Ga melt-spun ribbons of as quenched and as annealed at different temperatures. No essential structure change was found before and after annealing, but there are some anomalies in the magnetization process. In the austenite state the M͑T͒ curves measured in 100 Oe field exhibit a Hopkinson peak at T C for the ribbons of as quenched and annealed at 573 and 773 K, but the curves monotonically decays to zero with the increasing temperature to T C after annealing at 1073 K. In the martensite phase of both as quenched and 573 K annealed ribbons an abrupt increase in the slope of the M͑H͒ curve was observed; it appears to be due to the onset of magnetic-field-induced twin boundary motion. The abrupt slope change disappeared in the ribbons annealed at temperatures higher than 773 K. The ribbon processing history and particularly the quenched-in internal stress were modeled to probe the possible mechanisms for the anomalous magnetization behaviors, combining the grain-grain strain stored in the polycrystalline. The annealing temperatures were clarified into three groups according to their effects on the magnetization behaviors of the austenite and martensite.

Effects of rotation speed on microstructure and transition temperatures in Ni–Fe–Al melt-spun ribbons

“…This is considered, because in the randomly textured, fine-grained, polycrystalline specimens, the local deformations due to the thermoelastic martensitic transformation are restricted by grain constraint effect [38]. However, anomalous magnetization behavior induced by magnetically induced variant reorientation is observed in the 14M martensite state of NieMneGa polycrystalline melt-spun ribbons [38,39]. Our as-spun ribbons showed no such anomalous magnetization curves up to 10 kOe at room temperature, i.e., the variant reorientation was not observed.…”

Magnetocaloric effect in “reduced” dimensions: Thin films, ribbons, and microwires of Heusler alloys and related compounds

“…Since the degree of disorder and internal stresses depend on thermal treatment, the characteristic temperatures of the phase transitions demonstrate an increase after annealing of the melt spun ribbons . The quenched‐in disorder and the coexistence of ferromagnetic and antiferromagnetic interactions bring about peculiarities of magnetic , transport , and magnetotransport properties.…”

Phase transition of Ni–Mn–Ga alloy powders prepared by vibration ball milling

“…Nevertheless, Ni-Mn-Ga alloys are very brittle, which remarkably impedes their practical applications. To overcome the problem, several forms based on the alloy have been proposed and investigated, including thin films [5][6][7][8][9], ribbons [10][11][12] and composites consisting of ductile polymer matrix and Ni-Mn-Ga alloy particles [13][14][15][16][17][18][19][20]. Among these forms, the composites prepared by mixing Ni-Mn-Ga alloy particles and polymer matrix exhibit great advantages with good formability and low cost of production, compared with the thin films and ribbons which are often restricted by their dimension in applications.…”