Papers by Author: K. Flachbart

Abstract: The transport and magnetic properties of the Eu1-xCaxB6 (0x0.4) single crystals were studied in the wide ranges of temperatures (1.8-300 K) and magnetic fields (up to 8 T). The experimental data allow to identify a metal-insulator transition (MIT) at the critical Ca concentration xMIT≈0.3, which agrees well with the predictions of double exchange model (V.M. Pereira et al. Phys. Rev. Lett., 93 (2004) 147202). A significant enhancement of magnetoresistive effect is observed below 100K for Eu1-xCaxB6 compounds corresponding to the metallic side of the MIT (xxMIT). The drastic decrease of paramagnetic Curie temperature evaluated from the magnetic and magnetotransport data is discussed in terms of quantum MIT scenario recently proposed for this low carrier density system.

Abstract: High precision measurements of magnetoresistance =f(T,H) and magnetization M(T,H) have been carried out on single crystals of rare earth dodecaboride TmB12 at temperatures 1.8–30 K in magnetic fields up to 80 kOe. The high accuracy measurements and precise temperature stabilization allowed us to perform numerical differentiation and analyze quantitatively a behavior of derivative d()/dH=f(T,H) and magnetic susceptibility (T,H)=dM/dH in paramagnetic and magnetically ordered phases of thulium dodecaboride. It was shown that negative magnetoresistance anomalies observed in present study in paramagnetic state of TmB12 can be consistently interpreted in frameworks of a simple relation between resistivity and magnetization - /M2 proposed by K. Yosida (Phys. Rev., 107, 396 (1957)). A local magnetic susceptibility loc(T,H)=(1/H(d(/)/dH))1/2 was deduced directly from the magnetoresistance measurements and compared with bulk susceptibility (T,H)=dM/dH results of the present study. Moreover, the susceptibility dependences loc(T,H) and (T,H) have been applied to analyze in detail the H-T magnetic phase diagram of TmB12.