  We have synthesized a new crystallographically ordered quaternary Heusler
alloy, MnNiCuSb. The crystal structure of the alloy has been determined by
Rietveld refinement of the powder x-ray diffraction data. This alloy
crystallizes in the LiMgPdSb type structure with F-43m space group. MnNiCuSb is
a ferromagnet with a high TC ~ 690K and magnetic moment of 3.85MuB/f.u. Besides
this we have also studied two other off-stoichiometric compositions; one Cu
rich and the other Ni rich (MnNi0.9Cu1.1Sb and MnNi1.1Cu0.9Sb) which are also
ferromagnets. It must be stressed that MnNiCuSb is one of the very few known,
non-Fe containing quaternary Heusler alloys with 1: 1: 1: 1 composition.
