Photoinduced spin dynamics in a uniaxial intermetallic heterostructure $$\hbox {TbCo}_2/\hbox {FeCo}$$

Abstract

Intermetallic heterostructures of rare-earth and transition metals exhibit physical properties prospective for various applications. These structures combine giant magnetostriction, controllable magnetic anisotropy, magneto-optical activity and allow spin reorientation transitions (SRT) induced by magnetic field at room temperature. Here, we present the results of a study of spin dynamics induced by ultrafast optical excitation in the $$\hbox {TbCo}_2\hbox {/FeCo}$$ TbCo 2 /FeCo heterostructure. The time dependence of the light polarization rotation excited by a pump optical pulse with a duration of 35 fs was measured in the total range of the SRT created by external DC magnetic field. We found hysteretic dependence of the polarization rotation on magnetizing field that is specific for spin dynamics near SRT. Enhancement of the rotation is observed in the critical points of the SRT and near the points of magnetization switch from metastable to stable spin states. In the time-domain, two characteristic delays of 20 ps and 200 ps were found, corresponding to the maximum deviation of the light polarization after excitation. The first is explained by the precession motion of spins out of the plane of the structure. The latter is accounted for the spin in-plane deviation from its initial position and thermal relaxation of the anisotropy.

Derivation of magnetic inertial effects from the classical mechanics of a circular current loop

“…This is coherent with the classical forms of the LLG equation, as generally used in micromagnetism [26,27]. As discussed in the Introduction, the problem of the inertial effect in the dynamics of magnetization has been investigated in recent literature [45][46][47][48][49][50][51][52][53][54][55]. In these works, an evolution equation for the magnetization has been proposed.…”

“…The origin of the differences between our approach and previous works is due to the fact that in Refs. [45][46][47][48][49][50][51][52][53][54][55] the intrinsic rotational motion of the charge defining the magnetic dipole is not considered as a basic assumption and therefore the inertial and Lorentz forces are introduced in a different way. An alternative approach useful to better draw a comparison with the equation proposed by Wegrowe and co-workers is discussed in the next Section.…”

“…It is important to remark that these inertial terms and the Lorentz terms due to the reorientation are both of the order of 1/ω and therefore they are often neglected in practical applications. Nevertheless, the possible use of magnetic fields with extremely high frequencies (at pico-and femto-second time scales) has recently generated a wide interest for the generalization of the LLG equation with inertial effects [45][46][47][48][49][50][51][52][53][54][55]. In this context, our approach yields two generalized sets of second order differential equations for the magnetization dynamics, including the inertial effects and the Lorentz terms due to the reorientation.…”

Composite Multiferroic Terahertz Emitter: Polarization Control via an Electric Field

“…S3 within the Supplemental Material [43]). This difference is explained by the effect of anisotropy disruption during optical pumping, as studied previously on a similar intermetallic structure [50]. The thermodynamic potential in the area of spin reorientation, H < 0.7 kOe, has two minima, in spite of piezoelectric deformation.…”

Polarization control of THz emission using spin-reorientation transition in spintronic heterostructure

“…The first observation of the spin dynamics excited by femtosecond laser pulse in the vicinity of SRT induced at room temperature by magnetic field has been reported in Refs. 29 , 30 . The experiments were carried out on the intermetallic TbCo 2 /FeCo heterostructure with uniaxial in-plane magnetic anisotropy.…”