  Magnetic fluctuations near to quantum criticality can have profound effects.
They lead to characteristic scaling at high temperature which may ultimately
give way to a reconstruction of the phase diagram and the formation of new
phases at low temperatures. The ferromagnet UGe2 is unstable to p-wave
superconducting order -- an effect presaged by the superfluidity in He3 --
whereas in CeFePO fluctuations drive the formation of spiral magnetic order.
Here we develop a general quantum order-by-disorder description of these
systems that encompasses both of these instabilities within a unified
framework. This allows us to demonstrate that in fact these instabilities
intertwine to form a new phase, a pair density wave.
