  Spin reorientation transitions and other related magnetic phenomena, which
owe their origin to the complex interplay between multiple magnetic
sublattices, have long attracted scientific attention both from the perspective
of fundamental curiosity and technological applications. In this study,
combining first principles calculations together with finite temperature Monte
Carlo simulations, we explore the possible origins of reorientation transition
of Cr spins in NdCrO$_3$. We construct a NdCrO$_3$ specific magnetic model,
consisting of symmetric superexchange interactions between magnetic ions, as
well as their magnetic anisotropy. We show that the observed spin reorientation
in NdCrO$_3$, arises out of a delicate balance between Nd$-$Cr magnetic
exchange interactions, single ion anisotropy of Nd spins, and single ion
anisotropy of Cr spins. Moreover, though our model does not take into
consideration the effect of anti-symmetric and anisotropic-symmetric magnetic
exchanges, the qualitative as well as quantitative agreement of the
theoretically derived and the experimentally observed spin-reorientation
transition in NdCrO$_3$, confirms the merit of our proposed microscopic model.
Our results also propose a hitherto unobserved collective magnetic ordering in
Nd sublattice, which is challenging to detect as it is an extreme low
temperature phenomena, therefore calls for further investigations.
