Magnetic Phase Diagram of the Triangular Antiferromagnetic Cs₂CuCl₄−ₓBrₓ Mixed System

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van Well, Natalija ; Zaharko, Oksana ; Delley, Bernard ; Skoulatos, Markos ; Georgii, Robert ; van Smaalen, Sander ; Rüegg, Christian:
Magnetic Phase Diagram of the Triangular Antiferromagnetic Cs₂CuCl₄−ₓBrₓ Mixed System.
In: Annalen der Physik. Bd. 530 (2018) Heft 12 . - 1800270.
ISSN 1521-3889
DOI: https://doi.org/10.1002/andp.201800270

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Abstract

Abstract The novel magnetic phase diagram of the Cs2CuCl4−xBrx mixed system is established by means of single crystal neutron diffraction in the lowest temperature region and zero magnetic field. Two long-range ordered magnetic phases exist in this mixed system depending on the Cl/Br concentration. In the rich Cl concentration range, the ordered magnetic state occurs below the ordering temperature TN = 0.51(1) K for Cs2CuCl3Br1 and at Cs2CuCl2.6Br1.4 below TN = 0.24(2) K. Magnetic order with a temperature-independent position (0, 0.573(1), 0) below the ordering temperature TN = 0.63(1) K appears in the rich Br concentration for Cs2CuCl0.6Br3.4. Between the rich Cl and rich Br concentration ranges (two magnetic phases), there is a range of x without magnetic order down to 50 mK. A suggestion about the magnetic exchange paths in the bc-layer for different regimes is presented, which can be controlled depending on the preferred Br occupation in the CuX4 tetrahedra. The density functional theory calculations of the exchange coupling constants J, J′ for some ordered compositions of the mixed system Cs2CuCl4−xBrx indicate that these are not frustrated.