Wigner Research Centre for Physics, Hungarian Research Network (HUN-REN) Budapest, Hungary

摘要：

In the present contribution, we intend to present some magnetoresistance results obtained in our  laboratory in the last five years. In these studies, our main interest was in the anisotropic magnetoresistance (AMR) in bulk (i.e., macroscopic size) ferromagnets such as microcrystalline (mc) and/or nanocrystalline (nc) fcc-Ni, fcc-Co and hcp-Co as well as Ni-Co alloys.

First, we will describe low-field results (H £ 10 kOe) at T = 300 K. Here, we will show that in nc-Ni, the AMR splitting of the resistivity (the difference between the longitudinal and the transverse resistivity in the magetically saturated state) scales linearly with the zero-field resistivity where the internal parameter is the grain size. In this context, we discuss the recently highlighted separation of AMR into extrinsic and intrinsic contributions. The next topic will be a comparison, for the first time, of the AMR of fcc-Co and hcp-Co. It turned out from our studies that AMR(fcc-Co) » 2 AMR(hcp-Co). Finally, we will discuss the influence of demagnetizing effects on the shape of the M(H) and MR(H) curves of strip-shaped thin foil samples.

In the second part of the talk, high-precision magnetoresistance results will be presented up to 70 kOe or 140 kOe magnetic fields on mc-Ni and nc-Ni metal and two Ni-Co alloys. It will be pointed out that at T = 3 K, for extracting the AMR parameters, a Kohler analysis should be carried out due to the presence of the Lorentz-force-induced ordinary magnetoresistance (OMR) contribution which is especially strong for pure microcrystalline (coarse-grained) Ni. At T = 300 K, the OMR contribution is negligible and here we analyzed the field-dependence of resistivity in high magnetic fields. Our results hint at the necessity for a refinement of the existing theories of the description of the field dependence.

报告人简介：

Dr. Imre Bakonyi received his Ph.D. (1976) from the Eötvös University in Budapest, Hungary, his C.Sc. (1991) and D.Sc. (2007) degrees from the Hungarian Academy of Sciences (HAS). He did postdoctoral research in France, Germany and U.K. He served as the Head of Metals Research Department at the Wigner Research Centre for Physics from 1995 to 2012 and in 2016, he was appointed to a research professor emeritus status. For his lifetime achievements in the research of metallic materials, Dr. Bakonyi was awarded the Officer’s Cross of the Hungarian Order of Merit in 2023. Dr. Bakonyi has a total of more than 210 research papers in English and more than 4,000 independent citations to published papers. His research expertise is in the preparation, thermal stability, atomic and electronic structure, electrical transport and magnetic properties of amorphous, nanocrystalline, multilayered and other metastable metallic phases, metal hydrides. He serves on the editorial board of 4 journals.

联系人：韩秀峰研究员、胡凤霞研究员