Directional solidification in gallium under strong magnetic field: NMR studies

Directional solidification in the strong magnetic field opens new perspectives in tailoring technologically important features of metals and metallic alloys. Here we use an Avance 400 NMR spectrometer to prove the orientation of metallic gallium upon crystallization, which was induced by the magnetic field of the spectrometer. About one third of the gallium sample was shown to have the particular orientation of the crystalline axes. The effect was observed for both α-Ga and metastable β-Ga. The orientation of the crystalline axes was revealed by the emergence of the narrow NMR lines similar to those in the gallium single crystals. The angular dependences of the NMR line frequencies were studied for α-Ga and were treated taking into account the quadrupole coupling and Knight shift. The crystalline a-axis was demonstrated to be aligned close to the magnetic field direction. The impact of the magnetic field on the gallium orientation at crystallization was found to be reproducible.