A further classification of glassy magnets: spin jam and spin glass

Non-ergodic behaviour can be easily found in many of the complex systems ranging from polymers to brain activities, to social networks and glass transitions due to their complex energy landscapes. Depending on the topology of these energy landscapes, the characteristics of these systems can be diverse in nature. Understanding their differences and classification remains a major scientific challenge. Recently, we presented a couple of experimental approaches combined with computer simulations to classify magnetic glassy materials into distinct classes. [1-3] The systems studied are high-temperature superconductor-related materials, spin-orbit Mott insulators, frustrated magnets, and dilute magnetic alloys. Our magnetic memory effect experiments reveal a distinct class of glassiness emerge in the densely populated magnets with a relaxation exponent of 1-n ≈ 0.6(1) which is different from 1-n ≈ 1/3 as of dilute magnetic glasses and from 1-n ≈ 1(Debye limit) as expected for a spin solid. Furthermore, we study the freezing temperature as a function of relaxation time spanning over ten orders of magnitude combining bulk susceptibility and several neutrons scattering experiments such as Neutron Spin Echo, Backscattering and direct geometry time of flight spectroscopies. Our experimental data reveals different relaxation profiles for different classes of glasses. [1] A. M. Samarakoon, et al. Scaling of Memories and Crossover in Glassy Magnets, Scientific Reports 7, 12053 (2017). [2] A. Samarakoon, et al. Aging, memory and nonhierarchical energy landscape of a spin jam, PNAS 113, 11806 (2016). [3] J. Yang, et al. Spin jam induced by quantum fluctuations in a frustrated magnet, PNAS 112, 11519 (2015).