Adiabatic demagnetization in the rotating frame by use of the rf electric field

在前一年，我们研究了由射频电场引起的旋转坐标系(ADRF)中绝热退磁的可能性，并观察到了一个很大的不可逆性。用扫频的方法在室温下对Al_2O_3单晶中的~-lt；27&gt；Al核自旋系统进行了双量子(DELTAm=*2)跃迁。射频电场诱导了含时的电四极相互作用。在这一年里，我们澄清了产生大不可逆性的原因如下，并验证了ADRF原则上是由射频电场实现的。在这个自旋系统中，使用双量子共振射频磁场也观察到了大的不可逆性，其程度与实验条件下由于射频电场而产生的ADRF的程度相同。ADRF在单量子跃迁中的不可逆性低于在双量子跃迁中的不可逆性。另一方面，在像CaF_2中的^&lt；19&gt；F自旋系统这样的二能级系统中，ADRF是众所周知的高度可逆的。根据这些结果，我们可以得出结论：这种大的不可逆性不是射频电场激发所固有的，而是由于^&lt；27&gt；Al自旋系统的多能级系统的特性所致。这种不可逆性是由于当频率到达谱线边缘时，塞曼系统和偶极系统在大温差下产生的热混合造成的，因此，在任何自旋系统的ADRF中都会出现这种不可逆性。然而，不可逆性的程度取决于局域场的Larmor频率与自由衰变时间的乘积。这种大的不可逆性是由于产品太大。一旦温差变小，ADRF随后就具有很高的可逆性。

In the preceding year, we examined the possibility of the adiabatic demagnetization in the rotating frame (ADRF) due to an rf electric field, and observed a large irreversibility. The experiment was carried out in a double quantum (DELTAm=*2) transition of the ^<27>Al nuclear spin system in Al_2O_3 single crystal at room temperature by means of frequency-sweep. The rf electric field induces the time-dependent electric quadrupole interaction. In this year, we have clarified the cause of the large irreversibility as shown below, and verified that the ADRF is realized in principle by the rf electric field.A large irreversibility is also observed by use of a double quantum resonant rf magnetic field in this spin system, the degree of which is the same as that of the ADRF due to the rf electric field under the experimental condition which is essentially the same. The irreversibility of the ADRF in the single quantum transition is lower than that in the double quantum transition. On the other hand, in a two-level system such as that of the ^<19>F spin system in CaF_2, the ADRF is highly reversible as well known. From these results, we can conclude that the large irreversibility is not inherent in the rf electric field excitation but due to the characteristics of the multilevel system of the ^<27>Al spin system. This irreversibility is produced by the thermal mixing which is caused between the Zeeman and dipolar systems under the large temperature difference when the frequency reaches the edge of the line, and therefore, appears in the ADRF in any spin system. However, the degree of the irreversibility depends on the product of the Larmor frequency due to the local field and the free decay time. The large irreversibility is due to the large product. Once the temperature difference becomes small, the ADRF proceeds with a high reversibility afterward.