Hamburg 2001 – wissenschaftliches Programm
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AM: Magnetismus
AM 9: Poster: Magnetowid. (1-17), Dü. Schichten (18-34), Oberfl
ächenmag. (35,36), Mikr. Methoden (37-45), Mikromag. (46-58), Phasenüberg. (59-77), Spektroskop. (78-91), Nanokr.Mat.(92-96), Anisotrop. (97-101), Schmelzen(102-104),Sonst/postdeadl.(105-109)
AM 9.77: Poster
Dienstag, 27. März 2001, 14:45–19:00, Foyer S 3
FIELD INDUCED PHASE TRANSITION IN A TYPE III FCC ANTIFERROMAGNET — •Matthias Meschke and Konrad Siemensmeyer — Hahn-Meitner-Institut Berlin, Germany
K2IrCl6 exemplifies a system for antiferromagnetic (af) ordering in fcc - symmetry. The frustration inherent to fcc-symmetry leads to a fluctuation reduced Nèeltemperature. In zero field a type III antiferromagnetic structure characterized by qaf = 2Pi (1, 1/2, 0) is stable with the Ir - moments (s = 1/2) oriented along the direction of the doubled cell [1]. This af-ground-state is selected by a small next nearest neighbour interaction.
In a field of 5 T K2IrCl6 shows a transition between the type III af phase and a multiple-q-structure. The critical field was determined using a SQUID based magnetometer. Neutron diffraction experiments in external fields up to 14 Tesla confirmed the existence of the phase transition. However, the typical reflection for the type III af-ground-state did not disappear even at maximum field. Therefore, it is unlikely that both phases simply coexist.
Using neutron polarisation analysis, the spin-alignment in both antiferromagnetic phases was observed to be perpendicular to the field-direction. The underlying interaction mechanism of the observed high field phase can only be understood, if the influence of thermal or quantum fluctuations is considered.
[1] J.W.Lynn, G.Shirane, Phys. Rev. Lett. 37 (1976) 154