👉 The Donald fluid, also known as the Donaldson fluid or the Donaldson liquid, is a hypothetical substance proposed by physicist David Donald in 1987 to describe the behavior of magnetic monopoles in certain condensed matter systems, particularly in spin ices. These materials exhibit a unique magnetic structure where magnetic moments (spins) can be arranged in a way that mimics the behavior of magnetic monopoles—isolated north or south poles. The fluid model suggests that these spin configurations can flow and interact in a manner analogous to magnetic monopoles, allowing for the existence of "magnetic charge" without the need for actual monopole particles. This concept has implications in both theoretical physics and materials science, offering insights into the behavior of exotic magnetic states.
