A lattice of interacting spins usually leads to a unique ferro- or anti-ferromagnetically ordered arrangements of those spins at a low temperature. There are certain lattice types where such orderings are strongly suppressed. A prototypical example is the Ising spin-½ system on a triangular lattice with a nearest neighbour antiferromagnetic interaction where the triangular arrangement results in competing interactions leading to a large number of distinct states with the same ground state energy. In recent times, there is an increasing focus on such magnetically frustrated systems, in search of quantum spin liquids which relieves the frustration by entangling the spins instead of ordering. Another approach to a ground state without order is to introduce sufficient magnetic disorder in a lattice. Such systems may get stuck in a differently disordered “glassy” state. In this letter, we explore what happens with extensive disorder introduced in the frustrated triangular lattice such that elements for both spin “liquid” and “glass” coexist.
Y2CuTiO6 has magnetically coupled spin-½ Cu2+ on a triangular lattice with 50% of the sites randomly replaced by nonmagnetic Ti4+. We establish that this system does not achieve either a magnetic ordering or a pure glassy state down to 50 mK, though the magnetic interaction strength is nearly 3000 times larger than this temperature. Various experiments and specific scaling behaviours of thermodynamic properties with temperature and magnetic fields suggest that the system remains in a disorder driven, dynamic cooperative paramagnetic state, opening new possibilities to explore the field of frustrated magnetism aided by disorder.
S. Kundu, Akmal Hossain, Pranava Keerthi S., Ranjan Das, M. Baenitz, Peter J. Baker, Jean-Christophe Orain, D. C. Joshi, Roland Mathieu, Priya Mahadevan, Sumiran Pujari, Subhro Bhattacharjee, A. V. Mahajan and D. D. Sarma, Phys. Rev. Lett. 125, 117206 (2020)
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Prof. D D Sarma’s group
Solid State and Structural Chemistry Unit (SSCU)
Indian Institute of Science (IISc)