To read the paper abstract, click on its title.

Ferromagnetic Resonance study of polycrystalline Fe_1-xV_x alloy thin films
J-M. L. Beaujour¹, J. Z. Sun², A. D. Kent^1
1 Department of Physics, New York University, New York, USA,
² IBM T. J. Watson Research Center - Yorktown Heights, NY 10598, USA

To be published in J. Appl. Phys. (May 2008)

• Abstract: 

  Ferromagnetic resonance has been used to study the magnetic properties and magnetization dynamics of polycrystalline Fe_1-xV_x alloy films with 0 ≤ x < 0.7. Films were produced by co-sputtering from separate Fe and V targets, leading to a composition gradient across a Si substrate. FMR studies were conducted at room temperature with a broadband coplanar waveguide at frequencies up to 50 GHz using the flip-chip method. The effective demagnetization field 4pM_eff and the Gilbert damping parameter G have been determined as a function of V concentration. The results are compared to those of epitaxial FeV fims.

 

Ferromagnetic resonance study of Co|Ni multilayers
J-M. L. Beaujour¹, W. Chen¹, K. Krycka², C-C. Kao², J. Z. Sun, A. D. Kent^1
1 Department of Physics, New York University, New York, USA,
² Brookhaven National Laboratory, Upton, New York 11973, USA
³ IBM T. J. Watson Research Center - Yorktown Heights, NY 10598, USA

Eur. Phys. J. B (2007)

• Abstract: 

  We report on room temperature ferromagnetic resonance (FMR) studies of [t Co|2t Ni]×N sputtered films, where 0.1 ≤ t ≤ 0.6 nm. Two series of films were investigated: films with the same number of Co|Ni bilayer repeats (N = 12), and samples in which the overall magnetic layer thickness is kept constant at 3.6 nm (N = 1.2/t). The FMR measurements were conducted with a high frequency broadband coplanar waveguide up to 50 GHz using a flip-chip method. The resonance field and the full width at half maximum were measured as a function of frequency for the field in-plane and field normal to the plane, and as a function of angle to the plane for several frequencies. For both sets of films, we find evidence for the presence of first and second order anisotropy constants, K₁ and K₂. The anisotropy constants are strongly dependent on the thickness t, and to a lesser extent on the total thickness of the magnetic multilayer. The Lande g-factor increases with decreasing t and is practically independent of the
  multilayer thickness. The magnetic damping parameter α, estimated from the linear dependence of the linewidth DH, on frequency, in the field in-plane geometry, increases with decreasing t. This behaviour is attributed to an enhancement of spin-orbit interactions with decreasing Co layer thickness and in thinner films, to a spin-pumping contribution to the damping.

e2007-00071-1

Magnetization damping in polycrystalline Co ultra-thin films: Evidence for non-local effects
J-M. L. Beaujour¹, J. H. Lee¹, K. Krycka², C-C. Kao², A. D. Kent^1
1 Department of Physics, New York University, New York, USA,
² Brookhaven National Laboratory, Upton, New York 11973, USA

Phys. Rev. B 74, 214405 (2006)

• Abstract: 

  The magnetic properties and magnetization dynamics of polycrystalline ultra-thin Co layers were investigated using a broadband ferromagnetic resonance (FMR) technique at room temperature. A variable thickness (1 £ t £ 10 nm) Co layer is sandwiched between 10 nm thick Cu layers (10 nm Cu|Co|10 nm Cu), while materials in contact with the Cu outer interfaces are varied to determine their influence on the magnetization damping. The resonance field and the linewidth were studied for in-plane magnetic fields in field swept experiments at a fixed frequency, from 4 to 25 GHz. The Co layers have a lower magnetization density than the bulk, and an interface contribution to the magnetic anisotropy normal to the film plane. The Gilbert damping, as determined from the frequency dependence of the linewidth, increases with decreasing Co layer thickness for films with outer Pt layers. This enhancement is not observed in structures without Pt layers. The result can be understood in terms of a non-local contribution to the damping due to spin pumping from Co through the Cu layer and spin relaxation in Pt layers. Pt layers just 1.5 nm thick are found to be suffcient to enhance the damping and thus act as efficient "spin-sinks." In structures with Pt outer layers, this non-local contribution to the damping becomes predominant when the Co layer is thinner than 4 nm.

cond-mat/0602243

Ferromagnetic resonance study of polycrystalline Cobalt ultrathin films
J-M. L. Beaujour¹, W. Chen¹, A. D. Kent¹, J. Z. Sun^2
1 Department of Physics, New York University, New York, USA,
² IBM T. J. Watson Research Center, Yorktown Heights, NY 10598, USA

J. Appl. Phys. 99, 08N503 (2006)

• Abstract:  We present room temperature ferromagnetic resonance (FMR) studies of polycrystalline ||Pt/10 nm Cu/t Co/10 nm Cu/Pt|| films as a function of Co layer thickness (1 £ t £ 10 nm) grown by evaporation and magnetron sputtering. FMR was studied with a high frequency broadband coplanar waveguide (up to 25 GHz) using a flip-chip method. The resonance field and the linewidth were measured as a function of the ferromagnetic layer thickness. The evaporated films exhibit a lower magnetization density (M_s = 1131 emu/cm³) compared to the sputtered films (M_s= 1333 emu/cm³), with practically equal perpendicular surface anisotropy (K_s ~ -0.5 erg/cm²). For both series of films, a strong increase of the linewidth was observed for Co layer thickness below 3 nm. For films with a ferromagnetic layer thinner than 4 nm, the damping of the sputtered films is larger than that of the evaporated films. The thickness dependence of the linewidth can be understood in term of the spin pumping effect, from which the interface spin mixing conductance (g^?? S^-1) is deduced.


[PDF]