project title: Nonlinear magnetic dynamics and BEC of magnons
project leader: Prof. Sergey Demokritov
access given (in days): 7
access used (in days): 7
local host: Prof. Grigory Volovik
home institution: Westfalische Wilhelms-Universitaet Muensterm Muenster
country of institution: Germany
starting date (yyyy-mm-dd): 2008-03-25
The new class of nonlinear magnetic phenomena has been discovered by two different groups in two different systems. The dynamic state of coherent precesion known as Homogeneously Precesing Domain has been found in Kapitza Institute in superfluid 3He at ultra-low temperatures. Demokritov group in the University of Mu?nster (Germany) obtained at room temperature the coherent state of the parametrically driven gas of magnons in ferromagnetic material. Both dynamical states were interpreted in terms of the Bose-Einstein condensation of magnons. The goal of the project is to study the common properties of the two phenomena, which may lead to construction of the general theory of Bose-Einstein condensation of magnons. Other ULTI visitors participating in the project: Bunkov (France), Lvov (Israel)
We found that the magnon Bose-Einstein condensation in ferromagnetic material and in superfluid 3He have common properties. In both systems the pumping of the magnons leads to non-zero chemical potential, which in turn leads to Bose condensation. In both systems, the transition temperature is very high, and thus in principle the BEC may occur at room temperature. There is however some important difference between these two systems. Ferromagnetic material does exist at room temperature. At such temperature the number of condensed magnons is typically much smaller than the number of thermal magnons. As a result this system is only slightly below the transition temperature, where the condensate fraction is small. Situation with magnon BEC in 3He is the opposite. Superfluid 3He exists only at very low temperature. As a result the number of pumped magnons is always much larger than the number of thermal magnons, which means almost 100% of condensate in 3He. Thus these two systems represent the same magnon BEC but in two different temperature regimes: close to zero temperature (superfluid 3He) and close to the transition temperature (yttrium-iron garnet).