Frustrated magnet for adiabatic demagnetization cooling to milli-Kelvin temperatures

Tokiwa, Yoshifumi; Bachus, S.*; Kavita, K.*; Jesche, A.*; Tsirlin, A. A.*; Gegenwart, P.*

no journal, , 

Due to the supply insecurity of Helium-3, adiabatic demagnetization refrigeration (ADR) for cooling to milli-Kelvin temperatures has been attracting much attention. Conventional refrigerants for ADR, paramagnetic salts, contain water molecule, which causes lack of stability in the air. Therefore, special care has to be taken for the handling. Here, we show that an HO-free frustrated magnet KBaYb(BO) can be ideal refrigerant for ADR, achieving at least 22mK. KBaYb(BO) does not degrade under severe conditions like high temperatures and ultra-high vacuum. Further, its magnetic frustration enables refrigeration to temperatures several times lower than the energy scale of magnetic interactions, which is the limit for conventional refrigerants.