Single crystal growth and magnetic function of Ni₅₂Mn₂₄Ga₂₄ intermetallic compound

The Ni₅₂Mn₂₄Ga₂₄ single crystals showed a large stain of 1% with a temperature hysteresis of only 10 K unneeded the association of external stress. The magnetic-field-enhanced strain up to 4% can be obtained by applied a field of 1.2 T in the [001] direction of the sample. The magnetostriction is up to 1% at the temperature close to the martensitic transition, which is much larger than that of (Tb, Dy)Fe₂. These results are related to the preferential orientation of the martensitic variants in the single crystalline samples. The metallurgical observation showed that the disordering internal stress in the sample can be eliminated by a two-step annealing, which avoids the random orientation of the variants. The directional internal stress caused by the directional solidification in turn makes a large fraction of variants preferentially oriented. In such samples, the applied magnetic field of 1.2 T is more effective to rearrange the variants than the residual internal stress during the martensitic transition. The sign of the strain can be changed by changing the field direction, which shows a potential application for fabricating a multi-poles actuator device. Based on the previous modeling, the mechanism of the magnetic field induced strain has been discussed.