A hybrid magneto-optical magnetometer and optical microscope has been designed and constructed for probing the magnetic properties of submicron nanomagnets. 10-nm-thick square nanomagnets have been fabricated individually and in small arrays fromNi80Fe14Mo5(“supermalloy”) by electron-beam lithography. Hysteresis loops with a good signal-to-noise ratio have been obtained fromindividualnanomagnets as small as 400 nm and from (5 &mgr;m)2arrays of nanomagnets ranging in size from 500 to 75 nm. ©1998 American Institute of Physics.