Multi-site exchange enhanced barocaloric response in Mn3NiN

We study the barocaloric effect (BCE) in the geometrically frustrated antiferromagnet \ud Mn\ud 3\ud NiN\ud across the Néel transition temperature. Experimentally, we find a larger barocaloric entropy change by a factor of 1.6 than that recently discovered in the isostructural antiperovskite \ud Mn\ud 3\ud GaN\ud despite significantly greater magnetovolume coupling in \ud Mn\ud 3\ud GaN\ud . By fitting experimental data to theory, we show that the larger BCE of \ud Mn\ud 3\ud NiN\ud originates from multisite exchange interactions amongst the local Mn magnetic moments and their coupling with itinerant electron spins. Using this framework, we discuss the route to maximize the BCE in the wider \ud Mn\ud 3\ud A\ud N\ud family.