Room-temperature ferromagnetism of Zn0.97Co0.03O pressed nanocrystalline powders

Abstract

${\mathrm{Zn}}_{0.97}{\mathrm{Co}}_{0.03}\mathrm{O}$ nanocrystalline powders were prepared by sol-gel method with a low annealing temperature of $450°\mathrm{C}$ . The as-synthesized ${\mathrm{Zn}}_{0.97}{\mathrm{Co}}_{0.03}\mathrm{O}$ powders were paramagnetic. However, after compaction under a pressure of $94\mathrm{MPa}$ , the ${\mathrm{Zn}}_{0.97}{\mathrm{Co}}_{0.03}\mathrm{O}$ pressed powders show a weak room-temperature ferromagnetism embedded in the paramagnetic background. The observed ferromagnetism is connected with compaction-induced defects at/near grain boundaries. Meanwhile, a room-temperature magnetoresistance $\Delta R∕R_0$ as high as $-73.7\%$ is observed in ${\mathrm{Zn}}_{0.97}{\mathrm{Co}}_{0.03}\mathrm{O}$ pressed powder sample.