  The authors show how to implement a 4-state universal logic gate (NOR) using
three strain-coupled magnetostrictive-piezoelectric multiferroic nanomagnets
(e.g. Ni/PZT) with biaxial magnetocrystalline anisotropy. Two of the
nanomagnets encode the 2-state input bits in their magnetization orientations
and the third nanomagnet produces the output bit via dipole interaction with
the input nanomagnets. A voltage pulse alternating between -0.2 V and +0.2 V is
applied to the PZT layer of the third nanomagnet and generates alternating
tensile and compressive stress in its Ni layer to produce the output bit, while
dissipating ~ 57,000 kT (0.24 fJ) of energy per gate operation.
