Spin-liquid to spin-glass transition in Y(Sc)(Mn1-xAlx)(2): Polarized neutron scattering study

The scattering of polarized neutrons has been measured in order to study the spin dynamics in Y0.97Sc0.03Mn2 and Y0.97Sc0.03(Mn0.9Al0.1)(2). A large magnetic scattering peak observed at around Q = 1.6 Angstrom(-1) indicates the existence of strong antiferromagnetic spin fluctuations. The energy and Q spectra obtained at 290 K exhibit nearly the same profiles for both samples, while those obtained at low temperatures are quite different; for Y(Sc)Mn-2 the intensity and the energy width decrease only slightly with decreasing temperature and the intrinsic width remains finite (2 Gamma = 20 +/- 5 meV) at the lowest temperature (10 K), whereas for Y(Sc)(Mn0.9Al0.1)(2), the intensity increases rapidly due to narrowing of the energy spectrum to the resolution limit (2 Gamma(res) = 5.8 meV) at 10 K, and instead, diffuse scattering was clearly observed at positions corresponding to the magnetic Bragg peaks of YMn2, implying a slowing down of spin fluctuations and the presence of short range magnetic order at the low temperature. These results are discussed in terms of a spin-liquid to spin-glass transition caused by Al substitution.