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The concentrations of paramagnetic centers and the values of other parameters, including the Debye temperature and the coefficient of the zero-field, temperature-proportional term, are reported as functions of d. The concentration of paramagnetic centers does increase with increasing d but, in striking contrast with the widely held expectation that the increase would be comparable to the increase in the concentration of O vacancies, it is as much as 2 orders of magnitude smaller. A new expression for the specific heat that takes into account the presence of spin-2 as well as spin-1 2 paramagnetic centers gives an accurate representation of the experimental data. [S0031-9007(99)08491-4]

The low-temperature specific heat of YMn2 has been measured at applied pressures of 0 to 7.7 kbar. A paramagnetic state is stabilized for moderate values of the applied pressure (of the order of 1.6 kbar). A large linear term in the specific heat, which decreases regularly with increasing pressure, is observed in this phase. It is ascribed to giant spin fluctuations associated with a magnetic-non magnetic instability and a strong geometrical spin frustration.