RESISTIVITY OF TmSe UNDER PRESSURE AT VERY LOW TEMPERATURE

Abstract

Centre de Recherches sur les Tres Basses Temperatures, C.N.R.S., BP 166 X, 38042 Grenoble-Cedex, France. (Laboratoire associe a l'Universite Scientifique et Medicale de Grenoble). + Permanent address : IBM Watson Center, Yorktown Heights, NJ 10598, USA. * Permanent address : Laboratoire de Physique des Solides, Orsay, France. Resume.- Nous decrivons des mesures de resistivite d'un echantillon presque stoechiometrique sous des pressions allant jusqu'a 6 kbars, jusqu'a une temperature de 25 mK. A 6 kbars, la resistivite atteint 120 mfl.cra a 30 mK alors que, au-dessus de T„, elle est de 1,65 mfl.om a 4,2 K. La resistivite croit exponentiellement avec la pression a tres basse temperature et lineairement au voisinage de T . Nous comparons ces resultats a la variation sous pression de l'aimantation a'un sous reseau mesuree par diffraction neutronique et a la resistivite d'autres composes de valence intermediaire. Abstract.- Resistivity measurements of a nearly stoichiometric sample up to 6 kbar and down to 25 mK are reported. For 6 kbar , the resistivity p rises up to 120 mSJ.cm at 30 mK whereas just above the ordering temperature T at 4.2 K its value is 1.65 mfl.cra. The increase of p is exponential with the pressure at very low temperature and linear in the vicinity of T . Comparisons are made with the pressure dependence of the sublattice magnetization measured by neutron diffraction and with resistivity of other intermediate valence compounds. The low temperature properties of the intermediate valent (IV) compound TmSe have been studied extensively in the last few years /1-7/. The occurence of a magneti­cally ordered ground state and the main features of the magnetic phase diagram have been well documented by various experimental methods ; in particular, the magnetic structure in zero magnetic field was shown by neutron diffraction to be simple type I antiferromagnetic (AF) /2/. As in many IV systems, the electrical transport properties are very anomalous due to the presence of a narrow 4f band at the Fermi level. The resistivity of nearly stoichiometric TmSe in the paramagnetic state increases on cooling from % 200 u°,.cm at room temperature to about 1500 u£2.cm at 4.2 K /4-5/ with a n almost logarithmic term between 6 and 40 K. This has been argued on qualitative grounds to originate from the Kondo effect. In zero applied field, the resistivity p jumps at T and increases very rapidly down to 10 mK where it may attain 14 inn.cm /6/. The intrinsic amplitude of this anomaly is unknown since it is dramatically reduced by small deviations from stoichiometry. This effect is destroyed by the magnetic field ; above the critical field of the metamagnetic transition, the resistivity in the FM phase lies below the RT value /7/. There is presently no definitive explanation for this rather sharp transition to a much higher resistivity below T at H = 0. The few pictures which have been proposed previously fall in two categories : i) those which consider the AF structur e to be responsible for the poor conductivity below T ; the situation would be closed to that described by Adler /8/ for Ti