Oscillations of the ferromagnetic resonance linewidth and magnetic phases in Co/Ru superlattices

Abstract

The interlayer exchange coupling ͑IEC͒ and the magnetic anisotropy of Co/Ru͑0002͒ hcp superlattices, produced by magnetron sputtering, were studied by ferromagnetic resonance ͑FMR͒. The main mode and a secondary mode, with a higher resonance field, were identified in the perpendicular FMR spectra. The secondary mode is attributed to the resonance of the bulk of Co magnetic layers while the main mode is associated with the Co/Ru interfacial phase. The linewidth dependence of the main FMR mode on the Ru thickness clearly reproduces the oscillations of the IEC between Co layers. These oscillations are attributed to the effects of lateral inhomogeneities of the IEC strength and have a period of about 12 Å. Moreover, they are in good agreement with magnetoresistance and magnetization measurements performed in the same samples. The dependence of the effective anisotropy constants on the Co layer thickness leads to the volume and surface anisotropy constants of K V = −1.10ϫ 10 7 erg/ cm 3 and 2K s = 0.95 erg/ cm 2 , respectively, and also to a critical Co thickness of approximately 9 Å below which the magnetization is oriented perpendicular to the plane of the film.

Magnetic phases and structural properties in Co/Ru superlattices

“…The spectra are characterized by two uniform absorption modes which are well resolved in the perpendicular orientation: the main mode with a lower resonance field and a secondary mode. The origin of these peaks has been discussed previously 6 and was attributed to the resonance of the Co/Ru interfacial regions and the bulk regions of the Co layers, respectively, indicating the presence of two magnetic phases with different effective magnetizations in the samples. The intensity of the modes shows a dependence with the Ru thickness, as will be discussed later in this section.…”

“…6 The main mode is associated with the Co/Ru interfacial regions, and the secondary mode, with the bulk regions of the Co layers. In this work we present FMR studies about the effect of the Ru layer thickness t Ru on the properties of the two Co magnetic regions in the ͓Co͑50 Å͒ / Ru͑t Ru ͔͒ 20 superlattices grown on Si͑100͒ substrates and XMCD experiments in the ͓Co͑50 Å͒ / Ru͑21 Å͔͒ 20 providing the Co effective spin magnetic moment at the interfacial region.…”

Pure spin current manipulation in antiferromagnetically exchange coupled heterostructures

“…This exchange coupling is similar to the RKKY interaction, whose sign and magnitude depend on the spacer thickness, and it is mediated by the conduction electrons of the metallic spacer. This type of interaction is present in trilayer systems such as Co/Ru/ Co, [20][21][22] Fe/Au/Fe 23 or Py/Cu/Py. 24 In this work, we will make use of the IEC between FM layers in order to modify the magnetization orientation during the resonance condition that can be used to control the polarization of the pure spin currents generated during the spin pumping process of the SAF/ML system.…”

Temperature Dependence of Magnetization Dynamics in Co/IrMn and Co/FeMn Exchange Biased Structures

“…Both are affected by many factors. Thus, for the free F layer the resonance field depends on the layer's saturation magnetization, surface anisotropy, and uniaxial magnetocrystalline anisotropy [11][12][13]. In the case of F/AF polycrystalline thin films, the structures resonance field is additionally affected by exchange bias due to the exchange interaction with AF spins and by rotatable anisotropy due to the presence of small unstable AF grains in which the AF magnetization rotates irreversibly as the FM magnetization is in rotation [14][15][16][17].…”