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Title: The frustrated quantum spin chain, linarite, in high magnetic fields
Authors: Willenberg, B
Nishimoto, S
Schaepers, M
Reehuis, M
Wolter, AUB
Drechsler, SL
Buechner, B
Studer, AJ
Rule, KC
Ouladdiaf, B
Suellow, S
Keywords: Monocrystals
Liquid crystals
Ground states
Issue Date: 29-Nov-2016
Publisher: Australian Institute of Nuclear Science and Engineering
Citation: Willenberg, B., Nishimoto, S., Schaepers, M., Reehuis, M., Wolter, A. U. B., Drechsler, S.-L., Buechner, B., Studer, A., Rule, K. C., Ouladdiaf, B., & Suellow, S. (2016). The frustrated quantum spin chain, linarite, in high magnetic fields. Paper presented at 13th AINSE-ANBUG Neutron Scattering Symposium, Sydney, NSW, Australia, 29-30 November 2016.
Abstract: Linarite, PbCuSO4(OH)2 is a natural mineral ideally suited to the study of frustration in J1-J2 systems due to an accessible saturation field and the availability of large single crystals well suited to neutron investigations. In this one dimensional J1-J2 model, competing ferromagnetic nearest-neighbour interactions (J1>0) and antiferromagnetic next-nearest-neighbours (J2<0) can give rise to novel phenomena such as multiferroicity for spiral spin states. It is also predicted that materials which exhibit such frustrated magnetic interactions are likely to display evidence of spin-nematic states. The magnetic spin-nematic phase can be likened to the arrangement of molecules in nematic liquid crystal displays (LCD). The magnetic form of the spin-nematic state, involves the ordering of spin-quadrupole moments in the absence of conventional spin-dipole order such that the magnetic spins align spontaneously along a chosen axis while still fluctuating dynamically. In Linarite, the Cu2+ ions form spin S = 1/2 chains along the b direction with dominant nearest neighbour FM interactions and a weaker next-nearest-neighbour AFM coupling, resulting in a magnetically frustrated topology [1, 2]. We present a neutron scattering and magnetic property study of linarite revealing a helical magnetic ground state structure with an incommensurate propagation vector of (0 0.186 ½) below TN = 2.8K in zero magnetic field [3]. From detailed measurements in magnetic fields up to 12 T (B || b), a very rich magnetic phase diagram will be presented (Fig. 1) [4]. A two-step spin-flop transition is observed, transforming the helical magnetic ground state into a collinear structure. As well, a magnetic phase with sine-wave modulated moments parallel to the field direction was detected, enclosing the other long-range ordered phases, and which exhibits phase separation in high magnetic fields. Theoretical calculations imply that linarite possesses an xyz exchange anisotropy. Our data establish linarite as a model compound of the frustrated one-dimensional spin chain, with ferromagnetic nearest-neighbour and antiferromagnetic next-nearest-neighbour interactions. We shall also discuss the high field phase (marked “?” in the phase diagram of Fig. 1) in terms of the spin-nematic physics as well as the hard to access regions of the phase diagram, namely Region II.
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