THE MAGNETIC STATES AND MAGNETOELASTICITY IN BCC INVAR-TYPE CR75FE25-XMNX ALLOYS

The substitution of Fe by Mn in the bcc ferromagnetic system Cr75Fe25 decreases the Curie temperature and eventually destroys long range FM order at 3 at% Mn. At higher Mn concentrations antiferromagnetic order sets in. Resistivity measurements, together with recent magnetization measurements show that for Fe concentrations 10<x<20 at% Cr75Mn25-xFex orders first antiferromagnetically at the Néel temperature and then ferromagnetically at a lower Curie temperature. A re-entrant spin glass state is also observed at lower temperatures in this concentration range. For x<10 at% Fe, antiferromagnetic order persists down to the lowest temperatures. At concentrations x<20 at% Fe, only ferromagnetic order is observed along with a re-entrant state at lower temperatures. Magnetostriction measurements in fields up to 6 T also reflect the complex magnetic features in this system. Thermal expansion measurements on these samples show magnetovolume effects as well as a substantial negative thermal expansion coefficient at low temperatures. © 1989.