Magnetic properties and giant moment clusters in Be2Mn 1-xFex compounds

2014 The magnetic properties of Be2Mn1 _xFex compounds have been investigated over the whole concentration (0 x ~ 1) and field (0 ~ H ~ 150 kOe) ranges at low temperatures (T ~ 100 K). The inhomogeneous nature of the magnetic transition previously observed in this system, has been confirmed by means of 03C32 versus H/03C3 plots up to 150 kOe. But low field (0 ~ H 1 kOe) magnetization measurements showed that this transition is gradual : gradual evolution from paramagnetism (x ~ 0.06) to mictomagnetism (0.11 ~ x ~ 0.30) then to ferromagnetism (0.30 ~ x ~ 1.00). The mean magnetic moment 03BC of ferromagnetic beryllides (0.30 ~ x ~ 1.00) shows a rapid non linear decrease with increasing Mn content but the corresponding normalized Fe moment (03BC/x03BC0 ratio) was found higher than unity, indicating that two kinds of atoms (Fe and Mn) are able to carry a magnetic moment in these beryllides. The magnetization data on Be2Mn1-xFex compounds with x ranging from 0.06 to 0.25, have been analysed in terms of magnetic clusters with temperature dependent moments and concentrations. The unusual results of this analysis have been discussed and tentatively interpreted by invoking the concepts of (i) giant moment clusters with their own Curie temperatures 0, increasing with the cluster size, (ii) nearly magnetic impurities which become magnetic by lowering the temperature, in the high fields considered here (H ~ 80 kOe), and (iii) antiferromagnetic short range interactions related to the mictomagnetic behaviour of these compounds. All of the results obtained in this work may be described in terms of local environment magnetism, but only with an appropriate model which takes into account two types of magnetic atoms (Fe and Mn). Development of such a model would be aided by the use of techniques other than magnetization measurements (Mössbauer spectroscopy, neutron diffraction studies, and so on...). LE JOURNAL DE PHYSIQUE TOME 40, JANVIER 1979, Classification Physics Abstracts 75 . 30C