Transient enhancement of magnetization damping in CoFeB film via pulsed laser excitation

Abstract

Laser-induced spin dynamics of in-plane magnetized CoFeB films has been studied by using time-resolved magneto-optical Kerr effect measurements. While the effective demagnetization field shows little dependence on the pump laser fluence, the intrinsic damping constant has been found to be increased from 0.008 to 0.076 with the increase in the pump fluence from 2 mJ/cm2 to 20 mJ/cm2. This sharp enhancement has been shown to be transient and ascribed to the heating effect induced by the pump laser excitation, as the damping constant is almost unchanged when the pump-probe measurements are performed at a fixed pump fluence of 5 mJ/cm2 after irradiation by high power pump pulses.

Femtosecond laser-heating effect on the magnetization dynamics in perpendicularly magnetized Ta/CoFeB/MgO film

“…This contradicts the obtained results. In addition, as shown in previous results [18,19], the variation of M S is negligible for analyzing the pump-fluence dependence of the effective magnetic anisotropic field. Therefore, the PMA K U is proportional to H .…”

“…For better understanding the behavior of H K and 0 a in the PMA CoFeB thin film under different pump irradiation fluences, we provide a possible explanation for the irrelevance between 0 a and H . K As demonstrated in our previous work of 10nm CoFeB film with in-plane anisotropy [19], the 0 a increased with the increase of F while the effective demagnetization field remained constant. The enhancement of 0 a upon laser heating is attributed to the transient rising values of T T .…”

“…damping. It has been previously reported that the damping constants in ferromagnetic thin films with in-plane magnetic anisotropy can be transiently enhanced by increasing the fluence of femtosecond laser-pulses [18,19]. The results showed that the transient thermal effect induced by the ultrafast laser-pulses within the ns timescale plays an important role in transiently manipulating damping parameter.…”

Gilbert damping in CoFeB/GaAs(001) film with enhanced in-plane uniaxial magnetic anisotropy

“…have proved experimentally that α is proportional to ξ 2 at room temperature by carrying out the Gilbert damping studies in FePdPt ternary alloys with fixed Fe content and varying the relative composition ratio between Pd and Pt. As listed in Table 1, the PMA field ( H P  = 4π M s −4π M eff ) and the in-plane UMA field ( H u ) are about 6000 Oe and 300 Oe, respectively, which are both significantly larger than those cases if the CoFeB film is directly deposited on Si, MgO or other substrates1527. Therefore, the increase of α in the present CoFeB film is mainly resulted from the strong spin-orbit coupling generated from the CoFeB/GaAs(001) interface, although the spin pumping effect originated from the CoFeB/Ta interface may also enhance the Gilbert damping a little bit67.…”

Magnetic domain wall engineering in a nanoscale permalloy junction

“…The magnetic switching fields show distinct thickness dependencies with a broad peak varying from 7 nm to 22 nm depending on the junction sizes, and the large magnetic switching fields favor the stability of the MRAM operation. The magnetoresistive random access memory (MRAM) [1][2][3][4][5][6] based on the tunneling magnetic resistance (TMR) effect has the potential to replace all existing memory devices in a computer or other hard disk drives as it could provide a high read/write operation speed and is also nonvolatile. [7][8][9] On the other hand, the magnetic domain wall gives a flexible approach in the data storage and the logic circuit.…”