  This article presents a brief overview of our recent work on the nature of
long period modulation in the premartensite and martensite phases of Ni2MnGa
ferromagnetic shape memory alloy using high resolution synchrotron x-ray powder
diffraction patterns. The commensurate structure model using the Pnnm space
group is unable to account for the peak positions of the satellite reflections
that appear due to modulations correctly. LeBail and Rietveld refinements using
the (3+1)-D super space group $Immm(00\gamma)s00$ show that the peak positions
of all the reflections, including the satellites, can be explained
satisfactorily using incommensurate modulations for both the premartensite and
martensite phases. The incommensurate modulation vectors are found to be q=
0.33761(5)c* = (1/3+$\delta$1)c* and 0.43160(3)c*= (3/7+$\delta$2)c*, where
$\delta$1 and $\delta$2 are the degrees of incommensuration for the
premartensite and martensite phases, respectively. The periodicity of the
closest rational approximant of the premartensite and martensite phases are
confirmed to be 3M and 7M, respectively, in agreement with single crystal
diffraction results.
