  The effect of Ge substitution on the magnetization, heat capacity,
magnetocaloric effect and magnetoresistance of GdMn2Si2-xGex (x=0, 1, and 2)
compounds has been studied. The magnetic transition associated with the Gd
ordering is found to change from second order to first order on Ge
substitution. Magnetic contributions to the total heat capacity and the entropy
have been estimated. Magnetocaloric effect has been calculated in terms of
adiabatic temperature change (deltaTad) as well as isothermal magnetic entropy
change (deltaSM) using the heat capacity data. The temperature dependence of
the magnetocaloric effect in all the three compounds have shown broad peaks.
The maximum values of deltaSM and deltaTad for GdMn2Ge2 are found to be 5.9
J/kgK and 1.2 K, respectively. The magnetoresistance is found to be very large
and positive with a maximum value of about 22% in the case of GdMn2Ge2. In the
other two compounds also, the magnetoresistance is predominantly positive,
except in the vicinity of the Gd ordering temperature. The anomalous nature of
the magnetocaloric effect and the magnetoresistance has been attributed to the
canted magnetic structure of these compounds.
