Analysis of the Low Temperature Magnetic Contributions to the Specific Heat of (Nd_xY_1−x)_2/3Ca_1/3MnO₃ (x=0, 0.1)

The low temperature specific heat of the colossal magnetoresistance compounds (Nd (x) Y1-x )(2/3)Ca1/3MnO3 (x=0, 0.1) for 0.4a parts per thousand currency signT < 2 K in magnetic fields up to H=9 T has been studied. Applied magnetic fields lead to the drop of the low temperature specific heat by more than 2 orders, which implies a large magnetic contribution. Experimental data were successfully fitted by the sum of the hyperfine C (hyp) , the linear T-dependent C (sg) and the spin waves C (sw) contributions. The C (sg) attributed to the glassy state of the magnetic systems of the studied insulating compounds exponentially decreases with the increase of H up to similar to 5 T. The C (sw) providing the best fitting of the experimental data is attributed to the ferromagnetic spin waves with pseudo gap Delta(H) in the spin-wave spectrum which increases linearly with the increase of the applied magnetic field. The Delta(0)similar to 0.8 K is approximately the same for both compounds studied.