~eurr~al of Magnetismand Magnetic Materials 5 (1977) 156-160 North-Holland Publishing Company NOTE ON MEASUREMENTS OF THE ELECTRICAL RESISTIVITY OF Cr-Mn ALLOYS * Marcel AUSLOOS b~rernation~l Cent~'efor Theoretical Solid State Physics - Belgium, h:stitut de Physique, Unil,ersit~ de L~bge, Sart Tilman, B-4000 Liege 1, Belgium Rcx-eived29 No~mber 1976; in revised form 28 March 1977 Various experimental results on C'r-Mn alloys are reviewed in order to discus:~recent precise measurements of the elec- trical resistivity in ~e vicinity of the spin ordering transition temperature T N. Different critical exponents k have been ob- served for the electr, cal resistivity temperature derivative in alloys of similar composition. Apparent discrepancies are inter- preted following recent theoretical work. 1. Introduction The temperature derivative of electronic transport coefficients diverges at the spin ordering ("critical") temperature of crystalline magnetic metals [1-6]. Critical exponents characterizing such a divergence have been theoretically predicted, but their value is controversial and is not always observed experimen- tally [6]. Mean field theory of the effective number ~t conduction electrons at the Fermi level can be one of the sources of some discrepancy between theoretical prediction and experimental results [7]. Furthermore, neglect of the occurrence of "confluent singularities" [S} is likely to be responsible for inducing some error m data anaIysis. Recent experimental results on the electrical resistivity of Cr-Mn alloys [3, 9-12] re- quest a broad discussion because of some puzzling features, and sometime~ orroneous identification of the Ndel temperature. In particular, different values of the critical exponent X of the electrical resistivity tem- perature derivative for similar alloys have to be explain- ed. Various experimental results on such alloys will be recalled in section 2. Emphasis will be put on the oc- currence of a Cr-Mn2 stable compound in the phase diagram. Apparent discrepancies between different X's * Work performed in the framework of the joint project ESIS (Eaectronic Structure in Solids) of the Univetsity of Antwerp and the Universityof Liege. will be interpreted in section 3, following recent theo- retical work on the electrical resistivity p. Finally, it will be clear that further experimental work is neces- sary before a definite conclusion (section 4) is reached. 2. Review of experimental results Cr-Mn alloys have very interesting properties. They are likely due to different spin and crystallographic structures which appear when the concentration of ele- ments is varied, i.e., when the electron per atom ratio changes. This has stimulated many magnetic and neu- tronographic studies, although most of them have been performed on systems containing only a small quantity of Mn. It was noticed in such cases [10] that a small addition of Mn impurities stabilizes the spin density wave structure of d-electrons, which characterizes pure chromium metals [ 13]. The coexistence of itinerant antiferromagnetism and of localized magnetic moments was also revealed by magnetic susceptibility measure- ments on a large temperature range for alloys with Mn concentration up to 30% [14]. When the concentra- tion of Mn atoms increases, the localized character of magnetic moments is obviously expected to increase. Investigation of magnetic properties of ternary V-ld_n -Cr has shown to what extent the band (Pauli's) paramagnetism exists. At a concentration of 10% in Mn, the system has to be described by a mixture of 156