NMR and Magnetic Studies of Mechanically Alloyed Co₇₅Ti₂₅

Abstract

We have measured zero field ⁵⁹Co NMR, X-ray diffraction (XRD) and magnetization in ferromagnetic mechanically alloyed Co₇₅Ti₂₅ powder as a function of milling time at 4.2 K. The XRD patterns showed that the sample is primarily in an amorphous phase after a short milling time of 10 h, and no clear amorphous–crystalline phase transformation is detected with further milling. The NMR results revealed that successive phase transformations occur with milling, and the amorphous phase consists of small clusters of such ferromagnetic phases as fcc-Co₃Ti, hexagonal-Co₂Ti, bcc-Co₃Ti, fcc-Co and fcc-Co–Ti solid solution depending on the milling time. The bcc-Co₃Ti phase, being metastable, is a disordered one in contrast to the ordered fcc-Co₃Ti phase and has a Co magnetic moment larger than that of fcc-Co₃Ti. We suggest that the precipitation of Co plays an important role in the cyclic phase transformation, which was previously reported.