On the electrical resistivity of Pt3FexMn 1-x alloys in the exchange inversion region

2014 The electrical resistivity (p) data as a function of temperature are reported for Pt3FexMn1-x alloys (with x = 0, 0.5, 0.6, 0.7, 0.8 and 1.0). The p(T) curve for Pt3Fe0.6Mn0.4 shows two 03C1-anomalies, one of which is attributed to the Curie temperature and the other to the transition to a heterogeneous non-colinear magnetic structure, thus favouring the hypothesis that the exchange reversal takes place via a system of structures with non-colinear orientation of the magnetic moments. J. Physique Lett. 45 (1984) L-781 L-784 15 AOÛT 1984, Classification Physics Abstracts 72.15E 75.25 The solid solutions Pt3FexMn1-x are isostructural over the entire concentration range (0 x 1), ordering in an fcc lattice (Cu3Au-type). The non-magnetic Pt atoms are ordered and occupy the 3(c) sites whereas the magnetically active Mn and FJ atoms are randomly distributed in I (a) sites. The initial alloys have very close lattice parameters viz. a = 3.89 A for Pt3Mn and a = 3.87 A for Pt3Fe [1]. The unchanged crystal structure and a feeble composition dependence of the lattice parameter are ideal conditions for studying a transition in the magnetic state in Pt3Fe,,Mn, from ferromagnetic in Pt3Mn (T~ = 390 K) to the antiferromagnetic in Pt3Fe (TN = 170 K), as Fe atoms are gradually substituted for Mn, i.e. as x is increased from 0 to 1 [1,2]. From an analysis of the neutron diffraction and magnetic measurements it was concluded that the sign of the exchange interaction JMn Fe reverses in the ferromagnetic-antiferromagnetic transition region (0.5 x 0.7) [3]. The heat capacity of Pt3FexMn1 _x alloys has been measured by Kourov et al. [4]. In this paper we report electrical resistivity ( p) data as a function of temperature (100-500 K) for alloys with compositions corresponding to x = 0, 0.5, 0.6, 0.7, 0.8 and 1.0, and discuss the observed p-anomalies in the light of the existing information on the magnetic structure. 1. Experiment The alloys were prepared by repeated melting of the high-purity constituent metals in an electric arcfurnace under argon atmosphere. The alloy buttons thus obtained were homogenized by Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyslet:019840045016078100 L-782 JOURNAL DE PHYSIQUE LETTRES annealing in evacuated silica capsules at 1 150 K for one week. All the annealed specimens were found to be single-phase by X-ray analysis. The samples for electrical resistivity ( ~ 1 x 1 x 8 mm3) were cut and reannealed for 72 hours before being taken up for measurements by standard fourprobe dc method. The relative values of resistivity are estimated to be accurate to ± 0.05 % but the uncertainty in sample dimensions limited the absolute resistivity values to be accurate to within ± 5 %. The fluctuation in temperature did not exceed 0.25 K during any particular measurement. No hysteresis was observed for cooling runs, hence only the heating runs are being reported in figure 1. Fig. 1. Electrical resistivity p as a function of temperature for Pt3FexMn1 _x for different values of x. Arrows denote the magnetic transition temperatures.