  Magnetic structure of single crystalline TmB4 has been studied by
magnetization, magnetoresistivity and specific heat measurements. A complex
phase diagram with different antiferromagnetic (AF) phases was observed below
TN1 = 11.7 K. Besides the plateau at half-saturated magnetization (1/2 MS),
also plateaus at 1/9, 1/8 and 1/7 of MS were observed as function of applied
magnetic field B//c. From additional neutron scattering experiments on TmB4, we
suppose that those plateaus arise from a stripe structure which appears to be
coherent domain boundaries between AF ordered blocks of 7 or 9 lattice
constants. The received results suggest that the frustration among the Tm3+
magnetic ions, which maps to a geometrically frustrated Shastry-Sutherland
lattice lead to strong competition between AF and ferromagnetic (FM) order.
Thus, stripe structures in intermediate field appear to be the best way to
minimize the magnetostatic energy against other magnetic interactions between
the Tm ions combined with very strong Ising anisotropy.
