High-field (40 T) magnetization studies of linear Heisenberg chains with alternating exchange

Metals in Catalysis, Biomimetics & Inorganic Material

Field-Induced Magnetic Ordering in the Quantum Spin System KCuCl3_3

KCuCl$_3$ is a three-dimensional coupled spin-dimer system and has a singlet ground state with an excitation gap ${\Delta}/k_{\rm B}=31$ K. High-field magnetization measurements for KCuCl$_3$ have been performed in static magnetic fields of up to 30 T and in pulsed magnetic fields of up to 60 T. The entire magnetization curve including the saturation region was obtained at $T=1.3$ K. From the analysis of the magnetization curve, it was found that the exchange parameters determined from the dispersion relations of the magnetic excitations should be reduced, which suggests the importance of the renormalization effect in the magnetic excitations. The field-induced magnetic ordering accompanied by the cusplike minimum of the magnetization was observed as in the isomorphous compound TlCuCl$_3$. The phase boundary was almost independent of the field direction, and is represented by the power law. These results are consistent with the magnon Bose-Einstein condensation picture for field-induced magnetic ordering.Comment: 9 pages, 7 figures, 9 eps files, revtex styl

LOW TEMPERATURE MAGNETIC SUSCEPTIBILITY OF [(CH3)3NH] 3Cu2Cl7 A ONE DIMENSIONAL S = 1/2 FERROMAGNET

On a mesuré la susceptibilité magnétique d'un composé, en poudre de [(CH3)3NH] 3Cu2Cl7de 2 à 300 K. La susceptibilité diverge fortement à basse température et on l'a interprétée comme due à une chaîne ferromagnétique fortement couplée (J/k = 72 K) d'ions de cuivre en coordination octaédrique plus une chaine antiferromagnétique plus faiblement couplée (J/k = - 13 K) d'ions de cuivre en coordination tétraédrique. Les interactions antiferromagnétiques entre chaines se traduisent par un maximum de χT observé à 3,8 K. Un modèle pour expliquer ce maximum indique un échange très faible (J'/k [MATH] - 0,1 K) entre les chaînes.The magnetic susceptibility of a powdered sample of [(CH3)3NH] 3Cu2Cl7 has been measured from 2-300 K. The susceptibility is strongly divergent at low temperatures and has been interpreted as due to a strongly coupled (J/k = 72 K) ferromagnetic chain of octahedrally coordinated copper ions plus a weakly antiferromagnetic (J/k = - 13 K) chain of tetrahedrally coordinated copper ions. Evidence for antiferromagnetic interactions between chains is seen in the maximum of χT observed at 3.8 K. A model to account for this maximum indicates very weak (J'/k [MATH] - 0.1 K.) interchain exchange