Phase Diagram for Spontaneous Nuclear Magnetic Ordering in Copper

Abstract

The static susceptibility of a single-crystal copper specimen has been measured at nanokelvin temperatures, parallel and perpendicular to the external magnetic field $B$. Below ${B}_{c}=0.27$ mT, three different antiferromagnetically ordered regions are described at small values of entropy $S$. The $B\ensuremath{-}S$ phase diagram is presented. Metastabilities and the observed nonadiabaticity during the final stages of demagnetization are discussed.