  In this letter, we address magnetization switching by oxygen adsorption in
porous metal-organic framework systems. To this end, we construct a simple
localized spin model combined with a Langmuir-type formula for oxygen
adsorption and study its finite-temperature properties using Monte Carlo
simulation. We successfully explain the main features of this phenomenon, such
as the discontinuous changes in magnetic states, sensitivity of the magnetic
transition temperatures to oxygen pressure, and absence of singularities in
adsorbed oxygen. Based on this model, we also reproduce the observed magnetic
transition temperatures for a typical value of oxygen adsorption energy.
