Lopeandia A F, André E, Garden J-L, Givord D, Bourgeois O
Institut NEEL, CNRS-UJF, 25 Rue des Martyrs, BP166, Grenoble 38042, France.
Rev Sci Instrum. 2010 May;81(5):053901. doi: 10.1063/1.3422247.
We report the microfabrication and operation of a highly sensitive ac-calorimeter designed to characterize small mass magnetic systems operating at very low frequencies (from 0.1 to 5 Hz) in a temperature range from 20 to 300 K. The calorimetric cell is built in the center of a 500 nm thick polymeric membrane of parylene C held up by a Cu frame. On both sides of the membrane defining a three layer structure, electrical leads, heater, and thermometer are deposited as thin film layers of NbN(x), with different nitrogen contents, taking benefit of the poor thermal conductance of niobium nitride to thermally isolate the system. This suspended structure ensures very low heat capacity addenda with values in the microJ/K over the 1 mm(2) area of the measurement cell. The structuring of the membrane along with suspending of the sensing part only by the parylene bridges leads to a highly reduced thermal link. The calorimeter has been characterized as a function of frequency, temperature, and magnetic field. The thermal link measured is really small reaching values well below 10(-8) W/K at 50 K. With these characteristics the frequency of adiabaticity is typically around few hertz and energy exchanges as small as 1 pJ can be detected. Measurements have been performed on Co/Au thin films and on the GdAl(2) microcrystal where the ferromagnetic phase transition is clearly evidenced.
我们报告了一种高灵敏度交流量热计的微加工和操作情况，该量热计旨在表征在20至300 K温度范围内、极低频率（0.1至5 Hz）下运行的小质量磁性系统。量热池构建在由铜框架支撑的500 nm厚聚对二甲苯C聚合物膜的中心。在限定三层结构的膜的两侧，利用氮化铌的低热导率，将电引线、加热器和温度计作为具有不同氮含量的NbN(x)薄膜层沉积，以热隔离该系统。这种悬浮结构确保了在测量池1 mm²的面积上具有极低的附加热容量，其值在微焦耳每开尔文量级。膜的结构化以及仅通过聚对二甲苯桥来悬浮传感部分导致热连接大幅减少。该量热计已被表征为频率、温度和磁场的函数。所测量的热连接非常小，在50 K时达到远低于10⁻⁸ W/K的值。基于这些特性，绝热频率通常约为几赫兹，并且能够检测到低至1 pJ的能量交换。已对Co/Au薄膜和GdAl₂微晶进行了测量，其中铁磁相变得到了清晰证明。
