  Following the theoretical predictions of ferromagnetism in Mn- and Co-doped
ZnO, several workers reported ferromagnetism in thin films as well as in bulk
samples of these materials. While some observe room-temperature ferromagnetism,
others find magnetization at low temperatures. Some of the reports, however,
cast considerable doubt on the magnetism of Mn- and Co-doped ZnO. In order to
conclusively establish the properties of Mn- and Co-doped ZnO, samples with 6
percent and 2 percent dopant concentrations, have been prepared by the
low-temperature decomposition of acetate solid solutions. The samples have been
characterized by x-ray diffraction, EDAX and spectroscopic methods to ensure
that the dopants are substitutional. All the Mn- and Co-doped ZnO samples
(prepared at 400 deg C and 500 deg C) fail to show ferromagnetism. Instead,
their magnetic properties are best described by a Curie-Weiss type behavior. It
appears unlikely that these materials would be useful for spintronics, unless
additional carriers are introduced by some means.
