Spin frustration in Y(Sc)Mn2

The relaxation rate of muon polarization of Y0.97Sc0.03Mn2 with a magnetic lattice composed of corner-shared tetrahedrons shows a broad peak around 2.5 K indicating a random spin freezing at low temperatures. The substitution by nonmagnetic Al atoms for 10% Mn atoms raises the spin freezing temperature to 45 K. The present work shows clearly that due to the strong geometrical frustration, the ground state of the system is singlet tetrahedrons mixed with frozen paramagnetic tetrahedrons.