Dresden 2009 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 12: Correlated Electrons: Spin Systems and Itinerant Magnets 2
TT 12.4: Talk
Monday, March 23, 2009, 14:45–15:00, HSZ 304
Ferromagnetic mixed-spin chain model for MnNi(NO2)4(en)2 (en = ethylenediamine) — •Andreas Honecker1, Wolfram Brenig2, Stefan Süllow3, Matthias Bleckmann3, and Ralf Feyerherm4 — 1Institut für Theoretische Physik, Georg-August-Universität Göttingen — 2Institut für Theoretische Physik, TU Braunschweig — 3Institut für Physik der Kondensierten Materie, TU Braunschweig — 4Helmholtz-Zentrum Berlin für Materialien und Energie
MnNi(NO2)4(en)2, en = ethylenediamine contains ferromagnetically coupled chains with alternating spins of magnitude 1 and 5/2. Two energy scales are observed in the field-dependent specific heat of this compound. This behavior is attributed to the existence of an acoustic and an optical mode in the spin wave dispersion. Parameters for a realistic model have been derived from the high-temperature behavior of the magnetic susceptibility.
Here we present numerical results for the specific heat obtained by exact diagonalization and Quantum-Monte-Carlo simulations for the alternating spin chain model. MnNi(NO2)4(en)2 orders antiferromagnetically at low temperatures in zero magnetic field, demonstrating relevant antiferromagnetic interchain coupling. This interchain coupling is included in the numerical treatment at the mean-field level.