Frustrated magnet for adiabatic demagnetization cooling to milli-Kelvin temperatures

Abstract Generation of very low temperatures has been crucially important for applications and fundamental research, as low-temperature quantum coherence enables operation computers formation exotic states, such superfluidity superconductivity. One the major techniques to reach milli-Kelvin is adiabatic demagnetization refrigeration. This method uses almost non-interacting magnetic moments paramagnetic salts where large distances suppress interactions between moments. The spatial separations are facilitated by water molecules, with a drawback reduced stability material. Here, we show that water-free frustrated magnet KBaYb(BO 3 ) 2 can be ideal refrigeration, achieving at least 22 mK. Compared conventional refrigerants, does not degrade even under high ultra-high vacuum. Further, its frustration structural randomness enable cooling several times lower than energy scale interactions, which main limiting factor base temperature refrigerants.