  Hybrid perovskites have been at the forefront of condensed matter research
particularly in context of device applications primarily in relation to
applications in the field of solar cells. In this article, we demonstrate that
several new functionalities may be added to the arsenal of hybrid perovskites,
in terms of external stimuli driven spin transitions as well as piezochromism.
As an example, we study Dimethylammonium Manganese Formate (DMAMnF), a hybrid
perovskite investigated quite extensively experimentally. We show by employing
first principles DFT+U calculations with the aid of ab initio molecular
dynamics calculations that DMAMnF shows temperature and pressure driven spin
transitions, from a low spin $S=1/2$ to a high spin $S=5/2$ state. This
transition is accompanied by a hysteresis, and we find that this hysteresis and
the transition temperature are quite close to room temperature, which is
desirable for device applications particularly in memory, display, and
switching devices. The operating pressure is a few GPa, which is accessible in
standard laboratory settings. We find that the cooperative behaviour showing up
as hysteresis accompanying the transition is driven primarily by elastic
interactions, assisted by magnetic superexchange between Mn atoms. Last but not
least we demonstrate that the spin transition is associated with piezochromism
which could also be important for applications.
