Mössbauer and magnetometric studies of uncommon magnetic properties of ordered (B2 type) Fe-Al alloys

This work presents experimental data on the Mossbauer and magnetic measurements of ordered Fe65.9Al34.1 (B2 type) alloy depending on temperature and external magnetic field. The results obtained show that the ground magnetic state of the alloy cannot be referred to any of the known types of magnetic ordering. A model of local magnetic moments is proposed, in which the amplitude and the sign of a local magnetic moment are determined by its local chemical surroundings. The model suggests the existence of local magnetic moments that are antiparallel to the total magnetization of the alloy: the magnetic moment of a Fe atom with five and more Al atoms in the nearest surroundings is antiparallel to the total magnetization. Within the framework of the model proposed, a quantitative agreement of the calculated and experimental values of the average magnetic moment of the Fe atom in the alloy has been obtained. It is shown that in the B2 superstructure there appear magnetic inhomogeneities of a nanometer scale, which consist of magnetic moments that are parallel and antiparallel to the total magnetization. The behavior of the magnetic and Mossbauer parameters depending on the temperature and the applied magnetic field indicates the existence of collective fluctuations of magnetic moments. The quantity of Fe atoms in such fluctuating ensembles, as evaluated from the data on the magnetization, is compared with their quantity in the magnetic inhomogeneities.