  Piezomagnetism couples strain linearly to magnetic order producing
magnetization. Thus, unlike magnetostriction, it enables bidirectional control
of a net magnetic moment. If this effect becomes large at room temperature, it
may be technologically relevant, similar to its electric analogue,
piezoelectricity. To date, however, the studies of the piezomagnetic effect
have been primarily restricted to antiferromagnetic (AF) insulators at
cryogenic temperatures. Here we report the discovery of a large piezomagnetism
in a metal at room temperature. Strikingly, by using the AF Weyl semimetal
Mn$_3$Sn, known for its nearly magnetization-free anomalous Hall effect (AHE),
we find that an application of small uniaxial strain of the order of 0.1 % can
control both the sign and size of the AHE. Our experiment and theory show that
the piezomagnetism can control the AHE distinctly from the magnetization, which
will be useful for spintronics applications.
