TY - JOUR
T1 - Antiferromagnetic spin resonance and magnetic phase diagram of deuterated κ-(BEDT-TTF)2Cu[N(CN)2]Br
AU - Ito, H.
AU - Kondo, T.
AU - Sasaki, H.
AU - Saito, G.
AU - Ishiguro, T.
N1 - Funding Information:
The in-plane and interplane resistivity, ~11a nd pi, as functions of temperature were measured under pressure up to 40 MPa on the same sample used for the AFMR study. For the resistivity measurement, the sample was cooled slowly with a rate of 0.7 K/min, due to the limitation of the cooling rate of the pressure facility. At ambient pressure, the pll showed nonmetallic behavior down to a partial superconductivity transition at To, exhibiting changes in the temperature-derivative at 60, 20, and 15 K. These temperatures are identified as crossovers between paramagnetic, low-dimensional flue tuating AF, long-ranged AF, and weak-ferromagnetic phases, like the Cl salt [7]. By connecting these temperatures on the resistivity curves measured under pressure, a magnetic phase diagram as shown in Fig. 2 was obtained. We found a reentrant superconductivity transition in a pressure region between 1 to 6 MPa, close to the ambient pressure region. Although present measurements were performed with a fixed cooling rate, the phase boundaries are sensitive to the cooling rate. Ac- cording to the measurements at ambient pressure [6], the phase boundaries on the diagram shift by at most 4 MPa of an equivalent change in pressure, depending on the cooling procedure. The behavior of the pi was slightly different from that of the ~11. The difference was within the error depending on the cooling procedure. As to the origin of the AF phase of the family of the salts, two models are proposed. One is that a nesting instability of the planar parts of the Fermi surface causes the AF phase [9]. The other is that the dimerization of BEDT-TTF molecules renders the conduction band half-filled and a Mott insulating phase emerges due to strong electron correlation [l]. The present spin structure determined by AFMR is consistent with both of them. The planar Fermi surface extends to the direction of a-axis, and Hartree-Fock calculation based on the Mott-Hubbard model predicts a possible AF spin order along the a-axis [lo]. The AFMR signals have a peculiar cooling rate and temperature dependence. That is, they are suppressed when the sample is cooled slowly and the temperature of the emergence is much lower than the probable Nkel temperature, 15-20 K. This behavior is understood by assuming that the pressure range of the occurence of the reentrant superconductivity transition is dependent on the cooling rate. Suppose that the reentrant transition occurs at ambient pressure when the sample is cooled rapidly. Then, the AFMR signal is suppressed below Toi because the microwaves axe screened by a superconducting fraction. The signals suddenly appear below TCZ where the superconductivity is suppressed and the magnetic phase emerges. On the other hand, when the sample is cooled slowly, it is considered that the reentrant transition is suppressed and usual superconductivity transition occurs instead. In this case the AFMR signal is suppressed by the superconductivity fraction all of the temperature region below Tc. The authors thank M. A. Tanatar and Yu. V. Sushko for discussions and M. Yao for use of the pressure facility. This work is supported by CREST (Core Research for Evolutional Science and Technology) of Japan Science and Technology Corporation.
Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 1999/6/24
Y1 - 1999/6/24
N2 - The antiferromagnetic phase of a deuterated salt of κ-(BEDT-TTF)2Cu[N(CN)2]Br is studied by magnetic resonance and resistivity measurements. When the sample is cooled rapidly, antiferromagnetic spin resonance (AFMR) signals are found below 6-8 K. With the aid of resistivity measurements under pressure, the magnetic phase diagram in the weak pressure region is obtained. The cooling-rate and temperature dependence of the AFMR signals are explained in terms of a reentrant superconductivity found close to ambient pressure.
AB - The antiferromagnetic phase of a deuterated salt of κ-(BEDT-TTF)2Cu[N(CN)2]Br is studied by magnetic resonance and resistivity measurements. When the sample is cooled rapidly, antiferromagnetic spin resonance (AFMR) signals are found below 6-8 K. With the aid of resistivity measurements under pressure, the magnetic phase diagram in the weak pressure region is obtained. The cooling-rate and temperature dependence of the AFMR signals are explained in terms of a reentrant superconductivity found close to ambient pressure.
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U2 - 10.1016/S0379-6779(98)00465-2
DO - 10.1016/S0379-6779(98)00465-2
M3 - Conference article
AN - SCOPUS:0033138289
VL - 103
SP - 1818
EP - 1819
JO - Synthetic Metals
JF - Synthetic Metals
SN - 0379-6779
IS - 1-3
T2 - Proceedings of the 1998 International Conference on Science and Technology of Synthetic Metals (ICSM-98)
Y2 - 12 July 1998 through 18 July 1998
ER -