Magnetic Evidence for Reentrant Field-Induced Spin Density Waves
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MAGNETIC EVIDENCE FOR REENTRANT FIELD-INDUCED SPIN DENSITY WAVES M.J. NAUGHTON,+ R.V. CHAMBERLIN,#, X. YAN,'X P.M. CHAIKIN*'@ AND L.Y. CHIANG,@ + State University of New York at Buffalo, Buffalo, New York 14260 # Arizona State University, Tempe, Arizona 85287 x University of Pennsylvania, Philadelphia, PA. 19104 * Princeton University, Princeton, New Jersey 08544 @ Exxon Research & Engineering, Annandale, New Jersey 08801 ABSTRACT High magnetic field (to 31T) d.c. magnetization measurements on the quasi-one dimensional organic conductor (TMTSF)2C104 yield thermodynamic evidence for the reentrance of a metallic phase from the magnetic field-induced spin density wave state. The H-T phase diagram developed previously from magnetotransport measurements is reproduced from 8 to 26 tesla. The reentrance occurs as a sharp collapse of M(H) to (near) zero magnetization in the high field metal phase. For fields above 27 tesla, deHaas-van Alphen-like oscillations appear, similar to earlier resistance data, as well as other features possibly signifying multiple transitions in the very high field regime. INTRODUCTION (TMTSF) 2 C1O 4 is the most studied of the many quasi-one dimensional metals known as the Bechgaard salts, which were the first organic superconductors.' Many other interesting phenomena have been observed in these materials in the past ten years, including the quantized Hall effect, Hall effect sign changes as a function of magnetic field, the Schubnikov-deHaas effect, magnetic fieldinduced spin density waves (FISDW), oscillatory magnetoresistance anisotropy, nonlinear conductivity, and the subject of this paper, the reentrance of the low field metal phase out of the FISDW phase in very large magnetic fields. All these effects owe their occurance in this material to the highly anisotropic crystal structure, which allows one to consider it quasi-one, -two, or three dimensional, depending on temperature, magnetic field (strength and direction), pressure, etc. Perhaps the least understood and most interesting of these effects is the reentrant phase. While a convergence of theoretical efforts' in the past five years has left us with a good (i.e. consistent with data) understanding of the emergence of the FISDW states for magnetic fields below 10T, the situation is much less clear above 10T (see references for a description of the FISDW transitions below 10T). The last of the SDW transitions occurs at 7.5T to a semimetallic state which appears to be stable all the way out to 26T at low temperature (T26T) regime is difficult to ascribe to such a metal. Further experimental information, such as recent specific heat experiments,' as well as a more complete understanding of the high magnetic field properties of a quasi-one dimensional metal, may help to unravel the physics beneath this discovery. In particular, more information is needed as to the nature of the reentrant phase. Are the FISDW and reentrant metal states at high field separated by a 1st or 2nd order phase transition? Since the threshold line at low fields is k
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