We consider a thin normal metal sandwiched between two ferromagnetic insulators. At the interfaces, the exchange coupling causes electrons within the metal to interact with magnons in the insulators. This electron-magnon interaction induces electron-electron interactions, which, in turn, can result in p-wave superconductivity. In the weak-coupling limit, we solve the gap equation numerically and estimate the critical temperature. In YIG-Au-YIG trilayers, superconductivity sets in at temperatures somewhere in the interval between 1 and 10 K. EuO-Au-EuO trilayers require a lower temperature, in the range from 0.01 to 1 K.

Magnons in antiferromagnetic insulators couple strongly to conduction electrons in adjacent metals. We show that this interfacial tie can lead to superconductivity in a tri-layer consisting of a metal sandwiched between two antiferromagnetic insulators. The critical temperature is closely related to the magnon gap, which can be in the THz range. We estimate the critical temperature in MnF2-Au-MnF2 to be on the order of 1 K. The Umklapp scattering at metal-antiferromagnet interfaces leads to a d-wave superconductive pairing, in contrast to the p-wave superconductivity mediated by magnons in ferromagnets. arXiv:1904.00233v1 [cond-mat.mes-hall]

We explore routes to realize electrically driven Bose-Einstein condensation of magnons in insulating antiferromagnets. Even in insulating antiferromagnets, the localized spins can strongly couple to itinerant spins in adjacent metals via spin-transfer torque and spin pumping. We describe the formation of steady-state magnon condensates controlled by a spin accumulation polarized along the staggered field in an adjacent normal metal. Two types of magnons, which carry opposite magnetic moments, exist in antiferromagnets. Consequently, and in contrast to ferromagnets, Bose-Einstein condensation can occur for either sign of the spin accumulation. This condensation may occur even at room temperature when the interaction with the normal metal is fast compared to the relaxation processes within the antiferromagnet. In antiferromagnets, the operating frequencies of the condensate are orders of magnitude higher than in ferromagnets.

Antiferromagnetic insulators can become active spintronics components by controlling and detecting their dynamics via spin currents in adjacent metals. This cross-talk occurs via spin-transfer and spin-pumping, phenomena that have been predicted to be as strong in antiferromagnets as in ferromagnets. Here, we demonstrate that a temperature gradient drives a significant heat flow from magnons in antiferromagnetic insulators to electrons in adjacent normal metals. The same coefficients as in the spin-transfer and spin-pumping processes also determine the thermal conductance. However, in contrast to ferromagnets, the heat is not transferred via a spin Seebeck effect which is absent in antiferromagnetic insulator-normal metal systems. Instead, the heat is transferred via a large staggered spin Seebeck effect.PACS numbers: 72.25. Mk,72.20.Pa,73.50.Lw,72.10.Di In spintronics, the properties which make antiferromagnets markedly different from ferromagnets also make them attractive in a more dynamic role. Antiferromagnets operate at much higher frequencies and may empower Terahertz circuits. They also have no magnetic stray fields, which therefore enables denser spintronics circuits. For these reasons, antiferromagnets are usually passive spintronics components. However, they can play a role as active components despite their lack of a macroscopic magnetic moment [1-13] and even when they are insulating [10,12,13].We demonstrate that the thermal coupling between antiferromagnetic insulators (AFIs) and normal metals is relatively strong. The strong thermal coupling facilitates several outcomes, can lead to efficient cooling of antiferromagnetic spintronics devices, might function as heat sensors and can reveal valuable information about the high-frequency spin excitations in DC measurements that are complicated to extract with other techniques.Antiferromagnets can produce pure spin currents as large as those produced by ferromagnets. We recently showed that spin pumping may be as operative from antiferromagnets as from ferromagnets [13], in apparent contraction to naive intuition. Furthermore, the efficiency of spin pumping from antiferromagnets to normal metals implies, via Onsager reciprocity relations, that there is a considerable spin-transfer torque on antiferromagnets from a spin accumulation in adjacent normal metals. However, in the absence of external magnetic fields, the spin Seebeck effect vanishes [14]. This fact seems to indicate that spins in antiferromagnets decouple from, or are only weakly connected to, heat currents and temperature gradients in adjacent normal metals.To the contrary, we find that the thermal coupling constant is orders of magnitude stronger than its ferromagnetic counterpart. This radical difference is caused by the large exchange field in antiferromagnets that governs the heat transfer rather than the much smaller anisotropy fields or external magnetic fields in ferromagnets. The thermal coupling between antiferromagnetic insulators and normal metals is associated with a staggered s...