Magnetism in β-DyD2+x and β-HoD2+x studied with positive muons

We have examined by muSR spectroscopy the four polycrystalline samples beta-HoD2.0, beta-HoD2 + 0.12, beta-DyD2.0, and beta-DyD2 + 0.135, specially to probe their magnetic short-range order (SRO) configurations. The temperature dependencies of the muon-spin relaxation rates for HoD2.0, HoD2.12, and DyD2.0 show similar behavior. For each compound i one can define a 'critical' temperature 7(ct) (around 5-8 K) at which the relaxation rate lambda(i), is maximum. In the extended critical region T-ci-4T(ci) the rate lambda(i)(T) can be fitted by the trial function lambda = alpha(i)(T - T-ci)/T-ci](-vi.). The critical exponents v(i) are compared to theoretical predictions. DyD2.135 shows different features. With decreasing temperature, starting at 300 K, an increasing fraction of the initial mu(+) polarization is lost, due to the increasing proportion of random local fields fluctuating with rates of 10(8)-10(9) s(-1) at the mu(+) site. Below 10 K a spontaneous Larmor precession signal, corresponding to a field of 0.66 T, is observed. Model calculations of the local field at the mu(+) are performed, assuming commensurate or incommensurate magnetic structures. One infers that a commensurate SRO is likely to develop below 10 K in DyD2.135. (C) 2002 Elsevier Science B.V. All rights reserved.