Antiferromagnetic (AF) nanostructures from ${\mathrm{Co}}_3{\mathrm{O}}_4$, CoO, and ${\mathrm{Cr}}_2{\mathrm{O}}_3$ were prepared by the nanocasting method and were characterized magnetometrically. The field- and temperature-dependent magnetization data suggests that the nanostructures consist of a core-shell structure. The core behaves as a regular antiferromagnet and the shell as a two-dimensional diluted antiferromagnet in a field (2D DAFF) as previously shown on ${\mathrm{Co}}_3{\mathrm{O}}_4$ nanowires [M. J. Benitez et al., Phys. Rev. Lett. 101, 097206 (2008)]. Here we present a more general picture on three different material systems, i.e., ${\mathrm{Co}}_3{\mathrm{O}}_4$, CoO, and ${\mathrm{Cr}}_2{\mathrm{O}}_3$. In particular, we consider the thermoremanent (TRM) and the isothermoremanent (IRM) magnetization curves as “fingerprints” in order to identify the irreversible magnetization contribution originating from the shells. The TRM/IRM fingerprints are compared to those of superparamagnetic systems, superspin glasses, and 3D DAFFs. We demonstrate that TRM/IRM vs $H$ plots are generally useful fingerprints to identify irreversible magnetization contributions encountered in particular in nanomagnets.

• Received 6 October 2009

DOI:https://doi.org/10.1103/PhysRevB.83.134424