Highly anisotropic magnetic phase diagram of a 2-dimensional orthogonal dimer system TmB4

We have measured magnetization processes of a Shastry-Sutherland lattice (SSL) TmB4. For B parallel to c, plateaus appear at (1)/(8) and (1)/(2) of the full moment 7 mu B/Tm at 1.7-1.4 and 2-3 T, respectively. For B parallel to a, a metamagnetic transition occurs at similar to 30 T which is followed by a plateau at similar to 32 T. These plateaus are originated from geometric frustration effect in SSL. Magnetic field and temperature dependences of magnetoresistance and specific heat were also measured in detail below T-N = 11.7 K. The magnetic phase diagram possesses complex features which have an antiferromagnetic phase, spin flop saturated one, and a few additional phases by long periodic modulations originated from frustration effect in SSL. (c) 2006 Published by Elsevier B.V.