Triangular rare-earth borates for milli-Kelvin adiabatic demagnetization refrigeration

用于毫开尔文绝热退磁制冷的三角稀土硼酸盐

• 批准号: 514162746
• 负责人: Professor Dr. Philipp Gegenwart
• 金额: --
• 依托单位: Lehrstuhl für Experimentalphysik VI
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/514162746?language=en
• 关键词: Triangular; rare; earth; borates; milli

Adiabatic demagnetization refrigeration (ADR) is a classical cooling technique with renewed recent attention as alternative to costly and elaborate 3He/4He dilution refrigeration. Established water containing ADR salts suffer from chemical instability which requires delicate treatment to avoid degradation and ensure good thermal contact. We have shown recently, that H2O-free KBaYb(BO3)2 is an excellent alternative with higher entropy density that allows ADR to below 20 mK. Sintered pellets with silver powder admixture to ensure good thermal coupling are easy to manufacture, inexpensive and long-term stable even upon heating up to 700°C, enabling also ultra-high vacuum applications. KBaYb(BO3)2 belongs to a family of rare-earth-based borates A+xBa2+yR3+(BO3)3-z (A=Na, K; R=rare earth) with a perfect triangular arrangement of magnetic moments, adjustable R-atom distances and order/randomness of non-magnetic inter-layer atoms. The choice of R allows one to tune from quantum (R=Yb) to classical (Gd) spin behavior and to incorporate low-lying crystal electric field excitations in the Kramers (Dy) or non-Kramers (Tb or Ho) case to ADR. Our explorative synthesis and low-temperature magnetic investigation aims to disentangle the influence of geometrical frustration, quantum fluctuations, Heisenberg versus dipolar couplings and structural disorder on ADR. Eventually we identify the best ADR substances of this material class with respect to an optimized entropy density for different target temperatures between 10 and 200 mK, as required for multiple applications in quantum technology.

绝热退磁制冷（ADR）是一种经典的制冷技术，近年来作为昂贵而复杂的3 He/4 He稀释制冷的替代方案而受到人们的关注。含有ADR盐的已建立的水遭受化学不稳定性，这需要精细处理以避免降解并确保良好的热接触。我们最近已经表明，不含H2O的KBaYb（BO 3）2是一种具有更高熵密度的优秀替代品，其允许ADR低于20 mK。带有银粉混合物的烧结颗粒确保良好的热耦合，易于制造，价格低廉，即使在加热至700°C时也能保持长期稳定，也能实现超高真空应用。KBaYb（BO 3）2属于稀土基硼酸盐A+ xBa 2 + yR 3+（BO 3）3-z（A=Na，K; R=稀土）家族，具有完美的磁矩三角形排列、可调的R原子距离和非磁性层间原子的有序/随机性。R的选择允许从量子（R=Yb）调谐到经典（Gd）自旋行为，并将Kramers（Dy）或非Kramers（Tb或Ho）情况下的低位晶体电场激发并入ADR。我们的探索性合成和低温磁性调查的目的是解开的影响，几何挫折，量子涨落，海森堡与偶极耦合和结构无序的ADR。最终，我们确定了这类材料的最佳ADR物质，其熵密度在10至200 mK之间的不同目标温度下最优化，这是量子技术中多种应用所需的。