Atmospheric Neutrino Detection in the MINOS Far Detector

The MINOS Far Detector is a 5.4 kt magnetized calorimeter located at the Soudan underground labratory at Soudan, Minnesota. Besides its use in the long baseline experiment, the Far Detector can observe atmospheric neutrinos that interact in the detector or in the rock below it. The magnetic field allows for separation of $\nu_{\mu}$ versus $\bar\nu_{\mu}$ samples for charged-current interactions that produce muons. This direct determination of charge allows for testing of CPT symmetry in the neutrino sector using these samples. Preliminary results and prospects are presented.