Quasicritical behaviour of the NMR and mu SR relaxation in YMn2Dx

The magnetic and structural properties of YMn2 are strongly influenced by i ntroduction of hydrogen (deuterium) in the structure, however, it only slig htly modifies the noncollinear antiferromagnetic structure of the compound. The temperature dependences of the NMR relaxation times T-1 and T-2 of deu terium and the zero-field relaxation of muons in YMn2Dx were measured at te mperatures above the magnetic ordering temperature T-N. The corresponding r elaxation rates are described by the empirical expression (T/T-N -1)(-eta), where the exponent eta increases linearly with deuterium concentration x. To explain this behaviour, the Moriya theory of spin fluctuations was used. The expressions for NMR and mu SR relaxation rates have been calculated. T he resultant formulae agree well with the experiment, giving reasonable val ues of fitting parameters. The results obtained are discussed in terms of s pin fluctuation excitation spectrum.