Size effect on GdMn$_{2}$O$_{5}$ nanoparticles

We fabricated six difference sizes of GdMn$_{2}$O$_{5}$ nanoparticles/nanobrick by hydrothermal method. Purity and particle size were determinate by x-ray diffraction and TEM/SEM images. Two Mn antiferromagnetic ordering peaks at around 38 and 40 K were observed in ac magnetic susceptibility experiments, where as particle size is larger than 60 nm. Curie-Weiss fitting revealed that the N\'eel temperatures are increased with increasing size. Similar phenomena were also found in the saturate magnetic moments obtaind from M-H experiments at 5 K. No hysteresis loops were found in any particle size. We believe these magnetic behaviors are correlated with size confinement effects. The estimated magnetic correlation length of Mn is in between 60 and 84 nm.