Nonreciprocal many-body systems have been predicted to support various novel phenomena of heat transfer. Persistent heat current represents striking heat flow at thermal equilibrium among at least three nonreciprocal bodies. However, the directionality of the persistent heat current, defined as the relative contrast between the heat flows between two bodies in opposite directions, is limited. Here, we introduce a general strategy to enhance the directionality by using inhomogeneous magnetization. Using fluctuational electrodynamics, we numerically show that among four magneto-optical nanospheres in inhomogeneous magnetic fields, the directionality can reach $680\%$. The calculation agrees with coupled mode theory. We further show that the strategy also applies to nonreciprocal systems consisting of magnetic Weyl semimetals. We show that for a system consisting of four magnetic Weyl semimetal nanospheres in inhomogeneous magnetization, the directionality can reach $717\%$, even without an external magnetic field. The directionality achieved using inhomogeneous magnetization is over 1 order of magnitude higher than in prior studies. Our strategy can be useful for enhancing nonreciprocal radiative heat transfer for thermal management and energy conversion.

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• Light propagation, transmission & absorption
• Magnetic coupling
• Magneto-optical effect
• Nanophotonics
• Near-field optics
• Optics & lasers
• Photonics
• Scattering theory
• Topological materials