All-optical measurement of interlayer exchange coupling in Fe/Pt/FePt thin films

Abstract

Time Resolved Magneto Optic Kerr Effect spectroscopy was used to all-optically study the dynamics in exchange coupled Fe(10 nm)/Pt(x = 0–5 nm)/FePt (10 nm) thin films. As the Pt spacer decreases, the effective magnetization of the layers is seen to evolve towards the strong coupling limit where the two films can be described by a single effective magnetization. The coupling begins at x = 1.5 nm and reaches a maximum exchange coupling constant of 2.89 erg/cm2 at x = 0 nm. The films are ferromagnetically coupled at all Pt thicknesses in the exchange coupled regime (x ≤ 1.5 nm). A procedure for extracting the interlayer exchange constant by measuring the magnetic precession frequencies at multiple applied fields and angles is outlined. The dynamics are well reproduced using micromagnetic simulations.

Strongly coupled magnon–phonon dynamics in a single nanomagnet

“…In order to extract the relevant magnetic parameters, an identical magnetic film was grown next to the nanostructures. Its precession resonances were measured at various fields and angles, and γ and M S were fit to the Kittel formula 22 where , , H is the applied field magnitude, θ M and θ H are the angles of the magnetization vector and the applied field with respect to the surface normal, γ is the gyromagnetic ratio, and M S is the saturation magnetization. The fitted frequencies yielded values of rad∙ Oe −1 ∙s −1 and emu∙cm −3 .…”

Large anisotropy of magnetic damping in ultrathin epitaxial Fe/GaAs (0 0 1) film

“…Generally, the precessional motion detected by probe beam lasts up to the nanosecond scale. 25,26 In the TR-MOKE measurements, the femtosecond pulse laser is generated by a Ti:sapphire regenerative amplifier with a repetition rate of 1 kHz, a central wavelength of 800 nm, and pulse duration of about 60 fs, respectively. The pump beam fluence is 15.3 mJ/cm 2 .…”

Laser-Induced Magnetization Dynamics in Interlayer-Coupled [Ni/Co]4/Ru/[Co/Ni]3 Perpendicular Magnetic Films for Information Storage

“…As we all known, for the exchange-coupled structures, two different precession modes, a normal acoustic mode with in-phase magnetization precession and an optical mode with out-of-phase precession, can be observed in the dynamic magnetic measurements. − As compared to the acoustic mode frequency ( f a ), the precession frequency of optical mode ( f o ) is very sensitive to the IEC interaction. For the FM-coupled Fe/Pt/FePt, NiFe/Cu/Co and other systems, ,, f o would be always higher than f a and the difference is proportional to the interlayer coupling strength. In contrast, if the two FM layers are coupled antiferromagnetically, such as CoFeB/Ru/CoFeB and Co/Ru/Co systems, , the relation between f o and f a is quite complicated.…”

“…Usually, the laser-induced magnetic dynamics consists of an ultrafast demagnetization process taking place within the 1 ps range , and a subsequent precession process triggered by the transient change of magnetic anisotropy, which lasts for tens to hundreds of picoseconds depending on the magnetic damping factor. ,− Recent studies indicate that the possibility of all-optical switching in AF coupled structures, in which the optically induced transient “unpinning” of IEC provides an effective driving force for the ultrafast switching process. − In the magnetization precession process, the magnetic dynamic properties can be promoted by controlling the interlayer coupling, which is one of the key technological considerations in spintronic devices. As we all known, for the exchange-coupled structures, two different precession modes, a normal acoustic mode with in-phase magnetization precession and an optical mode with out-of-phase precession, can be observed in the dynamic magnetic measurements. − As compared to the acoustic mode frequency ( f a ), the precession frequency of optical mode ( f o ) is very sensitive to the IEC interaction. For the FM-coupled Fe/Pt/FePt, NiFe/Cu/Co and other systems, ,, f o would be always higher than f a and the difference is proportional to the interlayer coupling strength.…”

“…While in the saturated state, f o would be lower than f a and the difference is also proportional to the coupling strength. As for the intensity of precession modes, the optical mode is usually smaller than that of acoustic mode and increases with the decrease of coupling strength . The mode frequency and precession intensity rely not only on the interlayer coupling type and strength but also on the particular SAF structure and magnetic anisotropies.…”