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Neutron Diffraction and Magneto‐Optical Study of the Effect of Chloride Doping. On the Incommensurate Magnetic Phase of NiBr 2
Author(s) -
Day P.,
Turner K.,
Visser D.,
Wood T. E.
Publication year - 1982
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2221130226
Subject(s) - dopant , neutron diffraction , materials science , condensed matter physics , phase (matter) , doping , crystal (programming language) , ferromagnetism , phase diagram , crystal structure , chemistry , crystallography , physics , organic chemistry , computer science , programming language
The magnetic structures of crystals of NiBr 2 doped with 2, 5, and 10 mol % NiCl 2 are investigated by neutron diffraction and optical spectroscopy, with special reference to the incommensurate helical phase. Behaviour of the magnetic satellite reflections around (003/2) shows that the propagation vector of the helical phase is reduced from 0.15 nm −1 in NiBr 2 to 0.12 nm −1 in the crystal doped with 5% NiCl 2 . The commensurate‐incommensurate transition temperature T ic is similarly reduced, from 22.5 to 17 K . The propagation direction is unaffected by the dopant, remaining along [110]. Although no resolved magnetic satellite reflections are found in the 10% Cl − ‐doped crystal, a difference plot between 7 and 10 K suggests that the incommensurate phase exists below 10 K. The Néel temperatures of the samples show no significant variation with dopant concentration. The intensity of the “cold” exciton‐magnon combination band between 6050 and 6100 Å, which is associated with the incommensurate phase is used to determine T ic and its behaviour in a magnetic field is used to plot magnetic phase diagrams in the H ab ‐ T plane. No cold band is observed in the 10% Cl − ‐doped crystal. A hot band. resulting from the ferromagnetic component of the intraplanar coupling, is also studied.