  We present a detailed study of structural, magnetic and thermodynamic
properties of a series of Heusler alloys Fe2-xMnxCrAl (x=0, 0.25, 0.5, 0.75 and
1). Structural investigation of this series is carried out using high
resolution synchrotron X-ray diffraction. Results suggest that with increasing
Mn concentration, the L21 structure of Fe2CrAl is destabilized. The DC
magnetization results show a decrement in paramagnetic (PM) to ferromagnetic
(FM) phase transition temperature (TC) with increasing Mn concentration. From
the systematic analysis of magnetic memory effect, heat capacity, time
dependent magnetization, and DC field dependent AC susceptibility studies it is
observed that, Fe2CrAl exhibits cluster glass(CG)-like transition approximately
at 3.9 K (Tf2). The alloys, Fe1.75Mn0.25CrAl and Fe1.5Mn0.5CrAl exhibit double
CG-like transitions near Tf1~22 K, Tf2~4.2 K and Tf1~30.4 K, Tf2~9.5 K
respectively, however, in Fe1.25Mn0.75CrAl, a single CG-like transition is
noted at Tf2~11.5 K below TC. Interestingly, FeMnCrAl shows the absence of long
ranged magnetic ordering and this alloy undergoes three CG-like transitions at
~ 22 K (Tf*), 16.6 K (Tf1) and 11 K (Tf2). At high temperatures, a detailed
analysis of temperature response of inverse DC susceptibility clearly reveals
the observation of Griffiths phase (GP) above 300 K (T*) in Fe2CrAl and this
phase persists with Mn concentration with a decrement in T*.
