The magnetocaloric effect in bcc iron and hcp gadolinium is simulated on pico- and nanosecond time scales using Langevin spin dynamics on a discrete lattice, with parameters determined from ab initio calculations. It is found that transient external magnetic fields can drive thermodynamic cycles even in strongly nonequilibrium spin configurations, and that these are correlated with changes to the dynamic spin temperature. The theoretical predictions are found to agree closely with existing experimental measurements.
