Effect of Co and Fe stoichiometry on terahertz emission from Ta/(Co_xFe_(1-x))_(80)B_(20)/MgO thin films

摘要

Laser pulse induced terahertz (THz) emission from Ta/(CoxFe1-x)(80)B-20/MgO thin films, with varying compositions x and annealing temperatures, is investigated. With increasing annealing temperature, the THz emission intensity exhibits significant dependence on x, with maxima at x of 0.1-0.3. The x dependence of the THz emission originated from the composition dependence of the spin currents induced in CoxFe1-x formed by the crystallization of amorphous CoFeB after the annealing. The origin of the laser-induced spin current is qualitatively discussed in terms of a ballistic transport of hot electrons and a spin-dependent Seebeck effect with different compositions.