The angular dependent magnetoresistance of the superconducting ferromagnet UCoGe is studied in detail at 40 mK to fields of 18 T in a single crystal sample with a low residual resistivity ratio [R(300 K)/R(1 K)=RRR=5]. A ferro-to-ferrimagnetic transition near 9 T that depends only on the field component along the uniaxial magnetic c axis is observed in both transport and susceptibility. Reverse hysteresis in the magnetoresistance in the critical field region indicates a coupling of the superconductivity to the magnetization for fields aligned closely to the ab plane. These results corroborate and advance previous findings on higher residual resistivity ratio samples.
Angular, magnetic field and temperature dependence of the interlayer Seebeck effect of the multiband organic conductor α −(BEDT −TTF)2KHg(SCN)4 is experimentally studied at temperatures down to 0.55 K and fields up to 31 T in a wide range of angles. The background magnetic field and angular component of the Seebeck effect as well as the magnetic quantum oscillations that originate from the closed Fermi surface orbits are analyzed. The background interlayer Seebeck effect components show that above certain tilt angle of the magnetic field and above the kink field there is another CDW state in α −(BEDT −TTF)2KHg(SCN)4, between previously known CDW0 and CDWx states, in agreement with magnetoresistance and magnetization studies in this material. Our observations show that this state possesses some of the properties of the CDW0 state. The Fermi surface in the third CDW state is still reconstructed but less imperfectly nested as expected as this state develops above the kink field. The temperature dependence of the interlayer Seebeck effect reveals that this state is developed at temperatures below 3 K and at field orientations around the second AMRO maximum. In addition, for the first time, a detailed T−θ phase diagram of α − (BEDT − TTF)2KHg(SCN)4 based purely on Seebeck effect measurements is presented. We find that other states and transitions, beside the CDW states, also exist in a given temperature and angular range that have not been previously reported. These observations change the whole picture about the transport processes in the organic conductor α −(BEDT −TTF)2KHg(SCN)4 and allow to better understand the complex nature of the CDW order in this and similar compounds.
Abstract. The magnetic field and angular dependences of the thermopower and Nernst effect of the quasi-two-dimensional organic conductor -(ET) 2 KHg(SCN) 4 are experimentally measured at temperatures below (4 K) and above (9 K) the transition temperature to fields of T. 31 In addition, a theoretical model which involves a magnetic breakdown effect between the q1D and q2D bands is proposed in order to simulate the data. Analysis of the background components of the thermopower and Nernst effect imply that at low temperatures, in the CDW state, the properties of - Quantum oscillations observed in the both thermoelectric effects, at fields above 8 T, originate only from the orbit.
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