We report the observation of an anomalous { 27}Al-NMR response of a single grain Al_{ 72.4}Pd_{ 20.5}Mn_{ 7.1} icosahedral quasicrystal at low temperatures. In an external magnetic field of 6 T and upon decreasing temperature, we observe a sharp 100 % increase of the resonance linewidth at 2.5 K. No further changes of the linewidth are observed down to 0.05 K. The linewidth enhancement is accompanied by a small but distinct increase of the spin-lattice relaxation rate T_{ 1}^{ -1} and by a maximum of the spin-spin relaxation time T_{ 2}(T). All these anomalies are absent in external fields of 2.5 T and below. Our observations indicate unusual variations in the stability of isolated magnetic moments in a quasiperiodic metallic environment.
Categories: cond-mat.mtrl-sci