  There is a storied scientific history in the role of mechanical instruments
for the measurement of fundamental physical interactions. Among these include
the detection of magnetic torques via a displacement of a compliant mechanical
sensor as a result of angular momentum transfer. Modern nanofabrication methods
have enabled the coupling of mechanical structures to single, miniature
magnetic specimens. This has allowed for strikingly sensitive detection of
magnetic hysteresis and other quasi-static effects, as well as spin resonances,
in materials confined to nanoscale geometries. The extraordinary sensitivities
achieved in mechanical transduction through recent breakthroughs in cavity
optomechanics, where a high-finesse optical cavity is used for readout of
motion, are now being harnessed for torque magnetometry. In this article, we
review the recent progress in mechanical detection of magnetic torques,
highlight current applications, and speculate on possible future developments
in the technology and science. Guidelines for designing and implementing the
measurements are also included.
