  We studied the physical behavior of PdO nanoparticles at low temperatures,
which presents an unusual behavior clearly related to macroscopic quantum
tunneling. The samples show a tetragonal single phase with P42/mmc space group.
Most importantly, the particle size was estimated at about 5.07 nm. Appropriate
techniques were used to determine the characteristic of these nanoparticles.
The most important aspect of this study is the magnetic characterization
performed at low temperatures. It shows a peak at 50 K in zero field cooling
mode (ZFC) that corresponds to the Blocking temperature (T$_{B}$). These
measurements in ZFC and field cooling (FC) indicates that the peak behavior is
due to different relaxation times of the asymmetrical barriers when the
electron changes from a metastable state to another. Below T$_{B}$ in FC mode,
the magnetization decreases with temperature until 36 K; this temperature is
the crossover temperature (T$_{Cr}$) related to the anisotropy of the barriers,
indicative of macroscopic quantum tunneling.
