Ultrafast changes of magnetic anisotropy driven by laser-generated coherent and noncoherent phonons in metallic films

Abstract

. (2016) Ultrafast changes of magnetic anisotropy driven by laser-generated coherent and noncoherent phonons in metallic films. Physical Review B, 93 (21 A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. ABSTRACTUltrafast optical excitation of a metal ferromagnetic film results in a modification of the magnetocrystalline anisotropy and induces the magnetization precession. We consider two main contributions to these processes: an effect of non-coherent phonons, which modifies the temperature dependent parameters of the magneto-crystalline anisotropy; and coherent phonons in the form of a strain contributing via inverse magnetostriction. Contrary to the earlier experiments with high symmetry ferromagnetic structures, where these mechanisms could not be separated, we study the magnetization response to femtosecond optical pulses in the low-symmetry magnetostrictive Galfenol film so that it is possible to separate the coherent and non-coherent phonon contributions. By choosing certain experimental geometry and external magnetic field, we can distinguish the contribution from a specific mechanism. Theoretical analysis and numerical calculations are used to support the experimental observations and proposed model.

Controlling acoustic waves using magneto-elastic Fano resonances

“…7,11,12 The phenomena resulting from interaction between coherent spin and acoustic waves have already been addressed in the research literature: the spin wave excitation of propagating acoustic waves 7,[13][14][15] and vice versa, 8,[16][17][18] acoustic parametric pumping of spin waves, [19][20][21] magnon-phonon coupling in cavities [22][23][24] and mode locking, 25 magnonicphononic crystals, 26,27 Bragg scattering of spin waves from a surface acoustic wave induced grating, [28][29][30] topological properties of magneto-elastic excitations, 15,31 acoustically driven spin pumping and spin Seebeck effect, 32,33 and optical excitation and detection of magneto-acoustic waves. [34][35][36][37][38][39][40] However, studies of the interaction between propagating acoustic waves and spin wave modes of finite-sized magnetic elements, which are the most promising for applications, have been relatively scarce to date. 10 Here, we explore theoretically a class of magneto-acoustic devices in which the signal is carried by acoustic waves while the magnetic field controls its propagation via the magnetoelastic interaction in thin isolated magnetic inclusions as shown in Fig.…”

Damping of Standing Spin Waves in Bismuth-Substituted Yttrium Iron Garnet as Seen via the Time-Resolved Magneto-Optical Kerr Effect

“…is not at the origin of the excitation. The excitation of the SSWs is related to an ultrafast change of magnetic anisotropy induced by incoherent and coherent phonons due to the temperature dependence of the magnetic anisotropy constants [51,52] and inverse magnetostriction [53][54][55][56], respectively. The coherent and incoherent phonons are generated via the absorption of the pump photons by the phonon-assisted electronic d-d transitions simultaneously by one-and two-photon absorption processes [56].…”

Tracking picosecond strain pulses in heterostructures that exhibit giant magnetostriction

“…1. In the probed RSM volume we find three separated peaks with their maximum intensity at the out-of-plane reciprocal space coordinate q z = 2.42 Å -1 , 2.64 Å -1 and 2.69 Å -1 , that are attributed to TbFe 2 (220), Al 2 O 3 (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and Nb (110) respectively, according to their bulk lattice plane spacings. The layer thicknesses set by the sample growth are 500 nm TbFe 2 on top of 50 nm Nb and 330 µm Al 2 O 3 as schematically depicted in Fig.…”

“…We investigate laser excited samples that consist of (110) oriented Terfenol (TbFe 2 ) layers grown by MBE on (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) oriented Sapphire (Al 2 O 3 ) with a buried Niobium (Nb) (110) buffer layer as previously described. 37,39 The basic sample structure is only capped by a 2 nm thin protective Titanium (Ti) layer, which does not significantly contribute to the experimental transients.…”

“…11,12 Strain waves that originate from coherent phonon excitation can attain transient stresses on the order of GPa, which have been shown to interact with other phenomena such as phase transitions, 13,14 quantum well bandgaps, 15 piezo- 16 /ferroelectricity 17 and magnetism. [18][19][20][21] Such interactions are not only of fundamental interest but may also become relevant for applications as soon as the understanding allows for controllability. 22,23 In order to study the response to pure strain pulses it is beneficial to spatially separate the laser excited transducer from the probed layer.…”