Jae-Woo Jeong

Ultrafast magnetization relaxation of L10-ordered Fe50Pt50 alloy thin film

We have investigated the ultrafast magnetization dynamics of L10-ordered Fe50Pt50 thin film by means of a time-resolved magneto-optical Kerr effect measurement. We have found a high Gilbert damping value of α∼0.26, together with a very high precession frequency of f∼85 GHz and the shortest relaxation characteristic time of τ∼6.5 ps ever reported. We believe that L10-ordered FePt film with the unique property of a very high precession frequency and the shortest relaxation time will be very useful for the realization of picosecond spin switching.

Large converse magnetoelectric coupling effect at room temperature in CoPd/PMN-PT (001) heterostructure

We report a large converse magnetoelectric (CME) effect at room temperature in a multiferroic heterostructure formed from thin layers of perpendicularly magnetized CoxPd1-x alloys deposited on a piezoelectric single-crystal of lead magnesium niobate-lead titanate PMN-PT(001). The CME results from a strain-induced reorientation of the CoPd magnetization. By varying the composition and thickness of the CoxPd1-x film, a large converse magnetoelectric coupling constant, α=8×10−7 s/m, at room temperature was found for 10 nm Co0.25Pd0.75. This large CME effect results from combining a highly magnetostrictive CoPd alloy with highly piezoelectric PMN-PT.

Second-harmonic generation from realistic film-substrate interfaces: The effects of strain

The optical second-harmonic generation from a thin crystalline film on a substrate is theoretically investigated for both s and p polarized incident light. The contributions of lattice misfit strain as well as of misfit dislocation strain to the second-order nonlinear optical susceptibility are described using a nonlinear photoelastic tensor and can be separated by a polarization analysis of the scattered light at the second harmonic frequency. For the s(v)!s(2v) and p(v)!s(2v) scattering geometries, the nonlinear optical signal will be determined by dislocation strain only, whereas for the s(v)! p(2v) and p(v)! p(2v) geometries both lattice misfit strain and misfit dislocation strain will contribute.

Ultrafast spin demagnetization by nonthermal electrons of TbFe alloy film

An ultrafast spin demagnetization process of an amorphous Tb35Fe65 alloy film has been investigated by means of an all-optical pump-probe technique. Interestingly, steplike demagnetization on a subpicosecond time scale is observed before a much slower change on a time scale of tens of picoseconds. The steplike demagnetization at the subpicosecond scale is explained by the extended three-temperature model considering the interaction between a nonthermal electron and a spin system. The characteristic of subpicosecond demagnetization of TbFe alloy film is expected to be very useful in the manipulation of the spin state in ultrafast regime.

Influence of lattice mismatch on magnetization-induced optical second harmonic generation from a magnetic film on a nonmagnetic substrate

The optical second harmonic generation from a thin magnetic film on a nonmagnetic substrate is theoretically investigated for both s- and p-polarized incident light. The contributions of lattice misfit strain as well as of misfit dislocation strain to the second-order nonlinear optical susceptibility are described using a nonlinear photoelastic tensor, together with the contribution of magnetization described by a nonlinear magneto-optical tensor.

Direct observation of controlled strain-induced second harmonic generation in a Co0.25Pd0.75 thin film on a Pb (ZrTi)O3 substrate

The authors have observed strain-induced second harmonic generation (SHG) signals from a Co0.25Pd0.75 alloy film deposited on a lead zirconate titanate (PZT) substrate. The strain in the sample was controlled by the inverse piezoelectric effect. The authors demonstrate that it is possible to separate the strain contribution to the SHG signal from the crystallographic contribution and that from the electric polarization in PZT. An estimate of the value of the nonlinear photoelastic tensor components is in very good agreement with previous calculations.

Second Harmonic Rotational Anisotropy of Polycrystalline Fe Films on Glass Substrates

유리판 위에 증착된 다결정 Fe 자성박막의 두께에 따른 표면 결정 구조가 Ti : Sapphire 레이저를 사용하여 조사되었다. 비선형 광학 유전율의 결정구조에 따른 대칭성에 대한 계산으로부터 박막 표면은 C 2v 에 매우 가까운 C s 구조를 갖음을 보였다. 이러한 광학적 회전 이방성은 임의 방향의 그레인으로 구성된 다결정 구조의 박막에서는 매우 이례적인 일이다. 이차조화파로부터 얻은 이 결과는 (110) bcc 형태로 자란 X선 회절 결과와도 일치하는 것으로 매우 얇은 상태일 때 가지고 있던 박막 표면의 등방 구조가 두께가 증가함에 따라 바뀌면서 bulk 상태의 구조를 점차적으로 갖게 됨을 보여주고 있다.

Nonuniform apparent relaxation from dephasing of magnetostatic wave modes in a confined microdisk

We report the nonuniform apparent relaxation due to the spatially inhomogeneous dephasing of magnetostatic wave modes in a confined Permalloy microdisk investigated by picosecond time-resolved scanning Kerr microscopy. Spin precession in the disk shows a considerable nonuniformity in the relaxation time along the direction of a bias magnetic field. The nonuniform apparent relaxation is well reproduced by micromagnetic simulation using uniform values of damping constant. This implies that the spinwaves in the microdisk plays a significant role in the relaxation process. The simulation study, based on the analysis of spinwave modes, reveals that the spatial relaxation variation is mainly caused by the spatially inhomogeneous dephasing between the fundamental mode and magnetostatic backward volume wave mode.

Hyper-Rayleigh light scattering by dislocation deformation

We present a phenomenological description of HRLS by long-range dislocation deformation fields. For the description of nonlinear interaction of light with dislocations we use a nonlinear photoelastic tensor for investigation of acoustically-induced optical second harmonic generation. A cubic crystal without inversion center (for example GaAs, which is characterized by the symmetry point group T/sub d/) with linear edge dislocation is considered.