Abstract
Invar and Elinvar alloys are important materials for precision instruments. But, practical applications of these alloys are often restricted because of their ferromagnetism. Therefore, researches to develop nonferromagnetic Invar or Elinvar alloys have recently received considerable attention.
Chromium is an antiferromagnetic metal and its physical properties around the Néel temperature are drastically affected by the addition of solute atoms. We have investigated the thermal expansivity Δl⁄l, the electical resistivity Δρ⁄ρ and the temperature dependence of magnetic susceptibility χ for Cr-Co dilute alloys. The thermal expansivity of these alloys in the vicinity of room temperature is very small, showing the Invar characteristics. Some alloys show also the Elinvar characteristics in the same temperature range where the Invar characteristics occur. It is for the first time that both Invar and Elinvar characteristics have been found in chromium dilute binary alloys. The magnetic susceptibility of these alloys is less than 5×10−6 emu/g, indicating that these alloys are practically nonferromagnetic.
In these alloys the Néel temperature varies irregularly with increasing cobalt concentration; it decreases slightly for cobalt concentrations up to 2.0%Co, increases up to 2.5%Co, and decreases with further increase in cobalt concentration. But the Néel temperature determined from the temperature dependence of Δρ⁄ρ and χ does not coincide with an inflection point on the thermal expansivity curve.
