Frustrated magnet for adiabatic demagnetization cooling to milli-Kelvin temperatures

TL;DR

This paper introduces a water-free frustrated magnet, KBaYb(BO$_3$)$_2$, as an effective refrigerant for adiabatic demagnetization cooling, achieving temperatures below 22 mK with improved stability and lower temperature limits than conventional materials.

Contribution

The study demonstrates that KBaYb(BO$_3$)$_2$ is an ideal, stable refrigerant for ADR, enabling cooling to milli-Kelvin temperatures beyond the limits of traditional materials.

Findings

Achieved at least 22 mK temperature with KBaYb(BO$_3$)$_2$

Material remains stable under high temperature and vacuum

Cooling below the magnetic interaction energy scale

Abstract

Generation of very low temperatures has been crucially important for applications and fundamental research, as low-temperature quantum coherence enables operation of quantum computers and formation of exotic quantum states, such as superfluidity and superconductivity. One of the major techniques to reach milli-Kelvin temperatures is adiabatic demagnetization refrigeration (ADR). This method uses almost non-interacting magnetic moments of paramagnetic salts where large distances suppress interactions between the magnetic ions. The large spatial separations are facilitated by water molecules, with a drawback of reduced stability of the material. Here, we show that an H$_2$O-free frustrated magnet KBaYb(BO$_3$)$_2$ can be ideal refrigerant for ADR, achieving at least 22\,mK upon demagnetization under adiabatic conditions. Compared to conventional refrigerants, KBaYb(BO$_3)_2$ does not degrade even under high temperatures and ultra-high vacuum conditions. Further, its frustrated magnetic network and structural randomness enable cooling to temperatures several times lower than the energy scale of magnetic interactions, which is the main limiting factor for the base temperature of conventional refrigerants.