Dynamics of frustrated magnetic moments in antiferromagnetically ordered TbNiAl probed by neutron time-of-flight and spin-echo spectroscopy - art. no. 224407

We have studied the dynamics of Tb spins in the intermetallic compound TbNi Al in the paramagnetic (pm) and ordered antiferromagnetic (afm) phases by m eans of neutron time-of-flight and spin-echo spectroscopy. It is a remarkab le and very unusual characteristic of TbNiAl that its afm phase (below T-N= 47 K) contains regular long-range ordered spins as well as frustrated spins . The latter are identified by a strongly reduced moment measured by neutro n diffraction. The new quasielastic measurements show that the frustrated m oments relax on a time scale of 0.01 ns to 0.1 ns. Their autocorrelation fu nction I(q,t) is q independent and exponential in time. While in the pm pha se the spin relaxation is complete, i.e., I(q,t) goes to zero in the time r ange of the measurement, in the afm phase I(q,t) stays above zero.