Monopole Traps for Position-Based Information Coding

TL;DR

This work addresses storing information in magnetic monopole positions by proposing a spin-ice–based heterostructure that traps monopoles in two distinct regions using a central fragmented barrier. Monte Carlo simulations show that field cooling can deterministically select the trapped state, and the barrier preserves this non-volatile memory after removing the field; a robust, reversible field-driven switching mechanism is demonstrated with an emergent ferromagnetic readout tied to monopole positions. The study highlights thermal stability limits ($T_{leak}$ and $T_{melt}$), potential scalability to multi-trap architectures, and prospects for quantum encoding in spin-ice systems, suggesting a path toward ultra-dense, non-volatile memory with high spatial information density. Overall, the results establish a controllable, readout-enabled monopole-trap platform that could inform future compact memory technologies and explorations of nonequilibrium monopole dynamics.

Abstract

We propose a spin-ice-based heterostructure capable of encoding magnetic monopole quasiparticle positions for non-volatile information storage applications. Building upon two-dimensional magnetic monopole gases formed at the interface between 2-in-2-out spin ice and all-in-all-out antiferromagnetic pyrochlore iridate, the design introduces a 3-in-1-out/1-in-3-out fragmented barrier layer into the spin-ice matrix, defining two energetically stable monopole traps. The occupancy of these traps can be deterministically controlled by an externally applied magnetic field. Monte Carlo simulations reveal robust bistable switching, thermal stability below 0.22 K, and fully reversible field-driven transitions, demonstrating the system's potential for reliable, repeatable memory operation. Crucially, the heterostructure exhibits emergent ferromagnetism linked to monopole position, enabling non-destructive readout of the memory state via spatially resolved magnetic imaging. Unlike topological carriers such as skyrmions, monopoles confined at the sub-nanometer scale offer three orders of magnitude higher information density. These results establish these monopole-trap heterostructures as a scalable platform for next-generation ultra-compact memory technologies.

Figures (3)

• Figure 1: Monte-Carlo-simulated averaged monopole profiles and a single snapshot of monopole distribution of a $R_2$Ir$_2$O$_7$/$R_2$Ti$_2$O$_7$/$R_2$Ir$_2$O$_7$ heterostructure, after the heterostructure is magnetic-field-cooled with (a) field pointing down and (b) field pointing up to ground state and then remove the field. Monte-Carlo-simulated averaged monopole profiles and a single snapshot of monopole distribution of a $R_2$Ir$_2$O$_7$/$R_2$Ti$_2$O$_7$/$R'_2$Ir$_2$O$_7$/$R_2$Ti$_2$O$_7$/$R_2$Ir$_2$O$_7$ heterostructure with fragmented pyrochlore barrier, after the heterostructure is magnetic-field-cooled with (c) field pointing down and (d) field pointing up to ground state and then remove the field. $H_\text{loc}$/$J_\text{eff}$ is set at 14 for $R_2$Ir$_2$O$_7$ to create 2DMG in the heterostructure and $H'_\text{loc}$/$J_\text{eff}$ is set at 4 for $R'_2$Ir$_2$O$_7$ to serve as monopole barrier layer. The insets are illustration of the heterostructures.
• Figure 2: (a) Monopole profiles of a field-cooled and then zero-field-warmed up $R_2$Ir$_2$O$_7$/$R_2$Ti$_2$O$_7$/$R'_2$Ir$_2$O$_7$/$R_2$Ti$_2$O$_7$/$R_2$Ir$_2$O$_7$ heterostructure, where $T_\text{leak}\sim 0.22$ K is the temperature where monopole start to leave the upper trap and enter the lower trap, and $T_\text{melt}\sim 0.45$ K is temperature where monopole–antimonopole pairs are thermally created in the spin-ice layer due to the break down of the ice rule. (b) Illustration of the monopole leak and spin-ice melt process. (c) 2D densities of monopoles (left) and antimonopoles (right) in the upper trap and lower trap as a function of zero-field warm-up temperature.
• Figure 3: 2D densities of monopoles in (a) the upper trap, (b) lower trap and (c) net magnetization as a function of magnetic field, as field is sweeping between -0.4 T to 0.4 T at various fixed temperatures. Field scanning directions are labeled by arrows.