  The properties of nanoparticles are determined by their size and structure.
When exposed to external pressure P, their structural properties can change.
The improvement or degradation of the properties of the samples depending on
time is particularly interesting. The knowledge of the influence of
structural-size effect, aging time, and pressure on the behavior of the
compounds is essential for fundamental and applied purposes.Therefore, the
first attempts have been made to shed light on how the functional properties of
the Mn-containing perovskites change depending on them. The nanoparticles of
different sizes, from 20 to 70 nm, have been obtained. After 3 years, their
structural properties underwent significant changes, including an increase in
particle size, bandwidth, and microstrains, as well as a reduction in
dislocation density.The greatest change in the structure is observed for the
smallest nanoparticles. The phase transition temperatures increase with
nanoparticle size, time, and pressure. The aging time has the strongest
influence on the changing Curie temperature for the smallest and most
magnetically inhomogeneous nanoparticles with dTc/dP = 100 K / GPa. Conversely,
the structural-size effect and external pressure have the greatest influence on
the biggest and most magnetically uniform nanoparticles with dTc/dP = 91 and 16
K / GPa, respectively. After 3 years, the biggest nanoparticles demonstrate the
most stable phase transition temperatures with improved magnetocaloric
parameters near room temperature. These structural-size effect, aging time, and
pressure are powerful instruments to tune the phase transition temperatures and
magnetocaloric effect of the nanoparticles. These outcomes may have
implications for the whole class of perovskites and could initiate a new
mainstream.
