Abnormal low-field M-type magnetoresistance in hexagonal noncollinear ferromagnetic MnFeGe alloy

The new magnetic degree of freedom provided by the noncollinear structure plays an important role in the development of spintronic devices. In this work, we conducted a systematic study on the magnetic and electrical transport properties of the hexagonal noncollinear ferromagnetic MnFeGe alloy. Abnormal Hall effect and moderate magnetoresistance (MR) were observed below the Curie temperature (~ 200 K) of MnFeGe, in both bulk and thin-film forms. Notably, the perpendicular MR in all samples firstly grows, then quasi-linearly descends with magnetic field increasing, making an irregular M-type MR in the low-field region. It is speculated that the abnormal MR is related to the magnetic domain change, and combined with micromagnetic simulations, the labyrinth domain and sparse bubble formation are verified to exist in MnFeGe. Our work offers an understanding of the low-field-positive MR in a ferromagnet, as well as raises the possibility of magnetic bubble formation in this noncollinear system.