Ultrafast angular momentum transfer in multisublattice ferrimagnets

Abstract

Femtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. However, one of the unsolved questions is that of conservation of the total angular momentum during the ultrafast demagnetization. Here we report the ultrafast transfer of angular momentum during the first hundred femtoseconds in ferrimagnetic Co 0.8 Gd 0.2 and Co 0.74 Tb 0.26 films. Using time-resolved X-ray magnetic circular dichroism allowed for time-resolved determination of spin and orbital momenta for each element. We report an ultrafast quenching of the magnetocrystalline anisotropy and show that at early times the demagnetization in ferrimagnetic alloys is driven by the local transfer of angular momenta between the two exchange-coupled sublattices while the total angular momentum stays constant. In Co 0.74 Tb 0.26 we have observed a transfer of the total angular momentum to an external bath, which is delayed by B150 fs.

Photoinduced Demagnetization and Insulator-to-Metal Transition in Ferromagnetic InsulatingBaFeO3Thin Films

“…Beaurepaire et al proposed a phenomenological "three-temperature model" in order to understand the ultrafast demagnetization of Ni, which considers three interacting reservoirs of electrons, spins, and lattice, and suggested the importance of direct electron-spin interactions. Since the electron, spin, and lattice systems are quite tightly coupled to each other in strongly correlated 3d transition metal oxides, it is interesting to investigate the photoinduced dynamics with respect to the electronic states and magnetism [4][5][6][7][8][9][10][11][12][13][14][15].…”

“…Beaurepaire et al proposed a phenomenological "three-temperature model" in order to understand the ultrafast demagnetization of Ni, which considers three interacting reservoirs of electrons, spins, and lattice, and suggested the importance of direct electron-spin interactions. Since the electron, spin, and lattice systems are quite tightly coupled to each other in strongly correlated 3d transition metal oxides, it is interesting to investigate the photoinduced dynamics with respect to the electronic states and magnetism [4][5][6][7][8][9][10][11][12][13][14][15].For this study, we chose fully oxidized single crystalline BaFeO 3 thin films, which show unusual behaviors of ferromagnetic and insulating properties with saturation magnetization and Curie temperature of 3.2 µ B /formula unit and 115 K, respectively [16]. The large magnetic moment of BaFeO 3 thin films results in quite large peak intensity of Fe 2p x-ray magnetic circular dichroism (XMCD), ∼ 18 % of the x-ray absorption peak * Electronic address: wadati@issp.u-tokyo.ac.jp; URL: http://www.geocities.jp/qxbqd097/index2.htm intensity [17].…”

Ab initioinvestigation of light-induced relativistic spin-flip effects in magneto-optics

“…(17), which determines the polar Kerr effect, or the semirelativistic expression for the momentum operator in Eq. (14). It is already well known that the magneto-optical Kerr effect is by itself a relativistic effect, since it is directly related to spin-orbit coupling [54,55] present in the ab initio calculated electronic structure (particularly, in the wavefunctions).…”

“…To evaluate their influence, all the calculations described in the next section are performed with switching on and off the terms in square brackets of Eq. (14). To be precise our ab initio implementation of the relativistic momentum operator matrix elements use the equation (10) in Ref.…”

“…[2][3][4][5][6][7][8]). More recently, ultrafast laser-induced demagnetization has been studied in multisublattice or multilayer materials employing element resolved probing techniques in the extreme ultraviolet and soft x-ray regimes [9][10][11][12][13][14].…”