Modulus Increase with Magnetic Field in Ferromagnetic Shape Memory Ni–Mn–Ga

Abstract

Ferromagnetic shape memory Ni–Mn–Ga has been shown to exhibit deformations of up to 9.5% when driven with quasistatic fields. This article is focused on the use of Ni–Mn–Ga as the active element in a dynamic transducer consisting of a solenoid and a low-reluctance, closed magnetic path. Despite the absence of a restoring force in this configuration, we have shown in prior studies recoverable compressible strains of 1/4 4100 m, which are attributable to internal bias stresses built in the material during manufacture. In this study, we experimentally establish the presence of a modulus defect in Ni50Mn28.7Ga21.3, whereby the elastic modulus increases as much as 255% upon increasing the applied magnetic field from zero to 380 kA/m DC. Experimental measurements are conducted under both mechanical and magnetic excitation, and analyzed in combination with vibratory models for the system. While in our experiments the attractive magnetic forces between the transducer poles may contribute to the total modulus increase, the presence of a modulus change associated with the Ni–Mn–Ga element is substantiated. Dynamic Ni–Mn–Ga transducers offer an attractive mechanism for electrical tuning of the modulus, with potential application in active vibration absorption problems.