February 15, 2010 to March 1, 2010
Europe/Stockholm timezone

The effect of geometric constraints on the spin glass transition in binary pyrochlores

Feb 18, 2010, 10:00 AM


Dr Simon Banks (University College London)


Recent neutron scattering experiments [1] have sharpened the picture of an algebraic spin liquid phase in CsNiCrF6, originally proposed by Zinkin et al. [2]. Anderson famously predicted that systems such as this, with equal numbers of two magnetic species populating a pyrochlore lattice, should favour configurations with two of each type of ion present on every tetrahedron [3]. With this in mind, we have studied a simple model of a system comprised of equal numbers of two species of Heisenberg spins, A and B, distributed randomly across a pyrochlore lattice, but subject to the ice-rules like constraint that each tetrahedron has two A and two B type spins. We have characterized the ground state magnetic behaviour for all possible combinations of the three exchange interactions governing the system. This reveals a large region of exchange parameter space for which the system is in a spin liquid like state consisting of a soup of single species, non-interacting, antiferromagnetic loops. This configuration is robust even in the presence of four ferromagnetic bonds per tetrahedron. We demonstrate that the highly constrained form of quenched disorder imposed on the ion placement removes the possibility of a spin glass transition from this cooperative paramagnetic regime. We go on to discuss how the underlying structural configuration leads to algebraic magnetic correlations, manifested in the familiar bow-tie structure factor. This model is also susceptible to strong finite size influences. A system with finite size will be unable to develop the correct loop distribution to produce the bow-tie structure factor. We are currently investigating how such effects manifest themselves and the implications for more controllable arrays such as can be achieved with, for example, artificial spin ice. [1] T. Fennel et al., unpublished. [2] M. P. Zinkin et al., Phys. Rev. B 56, 11786 (1997) [3] P. W. Anderson, Phys. Rev. 102, 1008 (1956)

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Dr Simon Banks (University College London)

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