Ground state and stability of the fractional plateau phase in metallic Shastry Sutherland system TmB4

We present a study of the ground state and stability of the fractional plateau phase FPP with M Msat 1 8 in the metallic Shastry Sutherland system TmB4. Magnetization M measurements show that the FPP states are thermodynamically stable when the sample is cooled in constant magnetic field from the paramagnetic phase to the ordered one at 2 K. On the other hand, after zero field cooling and subsequent magnetization these states appear to be of dynamic origin. In this case the FPP states are closely associated with the half plateau phase HPP, M Msat , mediate the HPP to the low field antiferromagnetic AF phase and depend on the thermodynamic history. Thus, in the same place of the phase diagram both, the stable and the metastable dynamic fractional plateau FP states, can be observed, depending on the way they are reached. In case of metastable FP states thermodynamic paths are identified that lead to very flat fractional plateaus in the FPP. Moreover, with a further decrease of magnetic field also the low field AF phase becomes influenced and exhibits a plateau of the order of 1 1000 Msa

Tuning the magnetocaloric effect in the Lu doped frustrated Shastry Sutherland system TmB4

TmB4 is an anisotropic, metallic magnetic system with geometrical frustration of the Shastry Sutherland type. Here an experimental study of the magnetocaloric effect MCE in Lu doped Tm1 amp; 8722;xLuxB4 x 0.06, 0.30 , evaluated from the temperature dependence of heat capacity and magnetization curves at 2 K, is presented. The results are described within a theoretical model based on an extended Ising Hamiltonian which considers interactions up to the fourth next nearest neighbors. Model parameters were optimized to achieve the best match to the experimental results over the whole range of Lu3 ion concentrations. After optimization a good quantitative agreement with the adiabatic temperature change and a good qualitative agreement with magnetization curves is obtained. Our study shows that the efficiency of the MCE can be tuned by dilution with nonmagnetic Lu ions. The theoretical model developed could be used to design new magnetocaloric material