Novel Frustrated Matter in Artificial Nanomagnets

Spin ice is a magnetic system in which the geometry of competing interactions makes it impossible to reach a single ground state. Ice states naturally occur in magnetic pyrochlore systems [12, 42, 81] which have since been emulated by manufactured metamaterials called artificial spin ice [105, 55, 63, 28, 30, 79, 87]. The field of artificial spin ice advanced patterned nanofabrication and X-ray magnetic circular dichromism (XMCD) imaging to the point where researchers can create nearly any two dimensional arrangement of bar magnets such as the kagome [55] and square [30] lattices, and visualize their magnetic orientations [30]. Here we explore three ice-like lattices, the 3D square [33], trident [32], and Cairo [90] lattices, their unique means of achieving geometric frustration, and the resulting emergent states of matter. Beyond ice type behavior, randomized frustration may lead to spin glass behavior [10]. Competing anti-ferro- and ferromagnetic interactions of ice systems lead to complex energy landscapes, slow thermal relaxation, and memory effects beyond simple magnetic hysteresis. We explore pathways of generating artificial spin glass to better experimentally understand this complicated state of matter. We begin by constructing an artificial spin system with Gaussian positional and uniform rotational disorder [91], analyze the nature of the magnetic correlation, then repeat the process through a tree like system with rotational disorder and heightened effective dimension [89]. As a whole, these meta-materials confirm predictions of foundational statistical mechanics while posing new questions of their precise out of equilibrium dynamics and potential for device applications