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Abstract:
In the present work, the magnetocaloric and transport properties of
Ni2.2Mn0.72-xVxGa1.08 (x = 0.0, 0.04, 0.08, 0.12) magnetic shape memory
alloys are investigated. The alloys show a coupled magnetostructural
transition from paramagnetic austenite to ferromagnetic martensite in a
composition range of 0 <= x <= 0.08. For higher V substitution (x =
0.12), the martensite transition is lower than the conventional
ferromagnetic transition. Large magnetic entropy change values of about
12.4, 16.2 and 19 J kg(-1) K-1 and corresponding refrigeration
capacities of 60.6, 82.5, and 103 J kg(-1) were observed for x = 0, 0.04
and 0.08 alloys, respectively. The above two parameters linearly
increase with increasing magnetic field. The indirect adiabatic
temperature change calculated from the heat capacity measurement is
found to be at its maximum for x = 0.12 at H = 8 T. The
magnetoresistance is observed to increase from 0 % (x = 0.12) to 28 % (x
= 0) at the maximum field of 8 T. The Sommerfeld coefficients are almost
the same for the parent and a V-doped sample, which reveals a low free
electron density, and the Debye coefficients decrease with an increase
in V doping, confirming the phenomenon of electron-phonon scattering.
The critical exponents at second order magnetic transition for x = 0.12
are calculated as beta = 0.482, gamma = 1.056, delta = 3.021, which
agrees closely with mean field theory.
