Sub-Kelvin magnetocaloric effect in frustrated intermetallic NdNi4Mg

Magnetic refrigeration materials operating in the sub-Kelvin regime are receiving renewed interest due to the growing global shortage of cryogenic 3He gas. In this paper, we report that single crystals of NdNi4Mg, an intermetallic with frustrated local moments, reveal a large magnetocaloric effect, enabling adiabatic demagnetization cooling from an initial temperature of 2 K down to 0.15 K under a field of 9 T. The strong spin fluctuations responsible for magnetic cooling originate from a short-range ordered state that develops at T<0.5K, featuring a competition between ferromagnetic and antiferromagnetic interactions. This state is characterized by a broad specific heat plateau with enhanced values of C/T (∼6.4Jmol−1K−2). Sintered polycrystalline samples—likely possessing a higher degree of atomic disorders—exhibit a comparable, though slightly reduced, cooling performance due to the development of incipient long-range order. Given the high density of magnetic Nd atoms and the potential for good thermal conductivity, our research highlights NdNi4Mg as a promising intermetallic magnetic coolant alternative to traditional insulating paramagnetic salts.