Influence of volume and Fe local environment on magnetic properties of Fe-rich Fe—Al alloys

摘要

Fe-rich Fe—Al alloys present a large variety of magnetic behaviors and mechanical deformation of those alloys affects largely their magnetism. At room temperature alloys can be ferromagnetic, paramagnetic or show magnetic inhomogeneities, and at low temperatures spin-glass and re-entrant spin-glass phenomena have been found. Unfortunately, the mechanisms proposed in the literature to explain the magnetism of these alloys and the increase of the magnetic signal after deformation have discrepancies. This paper, based on Mossbauer spectroscopy measurements, with the support of X-ray diffraction and magnetic measurements performed on annealed and deformed samples and in a wide concentration range, proposes and describes a new way to understand the magnetic behavior of this alloy system. The data obtained from annealed samples confirm that Fe local environment have influence on the intensity of the competing exchange interactions (ferro- and antiferromagnetic). However, it is necessary to take into account the effect of the first and second nearest neighbor shells to explain the different magnetic behaviors found in this system. The data obtained from deformed samples show in addition that Fe—Fe interatomic distance also plays an important role on the magnetic properties of these alloys. When the interatomic distance is increased, the ferromagnetic exchange interaction is favored. The mechanisms described in this report will explain phenomena as the origin of the magnetic inhomogeneities on some of these alloys, as well as its behavior at low temperatures and the increase of magnetization caused by mechanical deformation.