Experimental Investigation On Ultrafast Dynamics Properties Of TbDyFe Thin Films

Femtosecond laser pump-probe measurement technique provides methods for studying dynamics of magnetic materials, which will provide basis for designing various micro-actuators and micro-drivers.TbDyFe films and multilayered films with different thickness were prepared by magnetron sputter, and a part of them were annealed at 550°C. TbDyFe films were characterized by scanning electronic microscope (SEM) and atom force microscope (AFM) methods. The results show that TbDyFe film prepared is amorphous structure and the surface is loosening, but the surface of the films which were annealed at 550°C show islands structure and crystal, and some grains were separated out.The influence of heat treatment, pump power and incidence angle of pump on TbDyFe films and multilayered films were investigated. The experimental results show that theΔR/R of TbDyFe films unannealed are made up of four parts, but theΔR/R curve of TbDyFe filims annealed are consisted of three parts. TheΔR/R curve of TbDyFe films annealed showed no rising after zero point but declining directly. Also, theΔR/R value at equilibrium was close to zero. The results resulted from two reasons, one is the heat treatment meliorate the characters of films, made the heat transmission easier. The other is the heat exchanging action between TbDyFe films and ambience, resulting in the temperature of films descending. Different pump power didn't change the shape ofΔR/R curve, but changed the maximum and the values of equilibrium. The bigger the pump power was, the bigger the maximum and the values of equilibrium were. The multilayered film had small influence on the maximum and values of equilibrium ofΔR/R of TbDyFe filims, so can protect the TbDyFe films by sputtering a film on the surface of TbDyFe films. The influence of incidence angle of pump on the maximum of theΔR/R curve is nonlinear.The temperature of electrons, lattices and spins were simulated with different coupling factors. The results showed , the more the pump power was ,the bigger the maximum of electrons temperature was and the bigger the difference between the maximum and the values of equilibrium, and the increasing of maximum is nonlinear, which were agreed with the experimental results. The interaction between the electrons and spins was the main way of making the spins temperature rising, resulted in the demagnetization of film and the demagnetization induced by lattice is relatively weak, so the demagnetization of film were the results of the action of electron-spin and lattice-spin.