Aging, memory, and nonhierarchical energy landscape of spin jam

Abstract

The notion of complex energy landscape underpins the intriguing dynamical behaviors in many complex systems ranging from polymers, to brain activity, to social networks and glass transitions. The spin glass state found in dilute magnetic alloys has been an exceptionally convenient laboratory frame for studying complex dynamics resulting from a hierarchical energy landscape with rugged funnels. Here, we show, by a bulk susceptibility and Monte Carlo simulation study, that densely populated frustrated magnets in a spin jam state exhibit much weaker memory effects than spin glasses, and the characteristic properties can be reproduced by a nonhierarchical landscape with a wide and nearly flat but rough bottom. Our results illustrate that the memory effects can be used to probe different slow dynamics of glassy materials, hence opening a window to explore their distinct energy landscapes. memory | energy landscape | spin jam | spin glass I f the energy landscape of a system resembles a smooth vase with a pointy bottom end, upon cooling the system goes quickly into the lowest energy state, i.e., the global ground state, that is usually associated with crystalline order. If the energy landscape is more complex with many metastable states, i.e., local minima, then cooling may lead the system into local minima resulting in a glassy order. The concept of such energy landscapes has been instrumental in explaining the glassiness that is ubiquitous in a wide range of systems, including atomic clusters (1), structural glasses (2, 3), polymers (4), brain activity (5), and social networks (6). Several different topological types of energy landscapes were proposed to characterize different glassiness and the associated slow dynamics (7,8). For instance, a rugged funnel-shaped landscape shown in Fig. 1A was proposed to understand the physics of biopolymers (9, 10) and dilute magnetic alloys called spin glass (11).Magnetic glass systems (12-16) present a unique opportunity to microscopically study the relation between the energy landscape and low temperature properties. The most studied magnetic glass state is the conventional spin glass realized in dilute magnetic alloys such as CuMn and AuFe. Here, dilute magnetic ions (Mn and Fe) in a nonmagnetic metal interact via the longrange Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction whose magnitude and sign change with distance between the randomly placed magnetic ions (11). The randomness drives the system into the spin glass state below a critical temperature, T f , that is comparable to the mean-field magnetic energy scale, i.e., the absolute value of the Curie-Weiss temperature, jΘ CW j. For instance, for Cu − 2 atomic (at.) % Mn (CuMn2% hereafter), Θ CW = −45 K and T f = 15.5 K. Another distinct glassy state called a spin jam has been recently suggested to appear in densely populated frustrated magnets (17-21). At the mean-field level, these systems are expected to remain in a classical spin liquid down to absolute zero temperature, due to macroscopic classical ground state dege...

Search optimization, funnel topography, and dynamical criticality on the string landscape

“…Its landscape topography is that of a funnel, akin to the free energy landscape of proteins and the loss function of well-trained deep neural networks. (Credit: Reproduced from [94]. )…”

Scaling of Memories and Crossover in Glassy Magnets

“…The TRM measurement is the most effective way to probe the memory effects in detail as explained in Supplementary Information and as shown most recently in the comparative study 35 of SCGO/BCGO and the canonical spin glass CuMn2%. While a dip-like memory effect with clear rejuvenation was observed, as expected, in CuMn2%, a shoulder-like memory effect seen in SCGO/BCGO implies lack of rejuvenation.…”

Jamming in Spin Systems

“…hrs [124] . , ranging from zero to 100hrs, at / ~ 0.7 where and are the waiting and the freezing temperature, respectively.…”

“…The aging effects of a spin jam prototype, SrCr9pGa12-9pO19 (SCGO(p=0.97)), and a spin glass prototype CuMn2% were taken from Ref. [124] , except the = 1.5 (5) data are new and are also plotted here for comparison. Each set of ∆ ( ) for each sample shown in panels It is interesting that the densely populated Y2Mo2O7 exhibits both spin glass and spin jam behaviors.…”

“…Authors: Tianran Chen, Gia-Wei Chern and Seung-Hun Lee [186] Understanding the dynamics of a glassy system via the energy landscape approach has led to promising insights into puzzling phenomena, such as temperature-dependent aging and memory effect. In this framework, the energy landscape is seen as a set of basins of attraction, and the system evolves through a succession of jumps between their local minima [187,188].…”