Magnetic Foehn effect in adiabatic transition

The magnetization process as a response to a sweeping magnetic field in the thermal environment is investigated by using the quantum master equation. In a slow sweeping velocity region where the system shows quasi-adiabatic m otion, a magnetic plateau in the magnetization process has been observed in the recent experiment of V-15 [Phys. Rev. Lett. 84 (2000) 3454]. Although the experiment was explained from a view of small capacity of the phonon he at bath. i.e., the phonon bottleneck effect, we found that a magnetic plate au appears almost regardless of the properties of the heat bath in the quas i-adiabatic transition and the appearance of the plateau is quite universal . We call it 'Magnetic Foehn effect'. On the other hand, the magnetic plate au also appears in a fast sweeping velocity region by the Landau-Zener-Stuc kelberg mechanism which is different from the above mechanism in a slow swe eping region, and we study the crossover between them. We also propose an e xperiment which clarifies the structure of coupling to the thermal reservoi r.