Stripline (SL), vector network analyzer (VNA), and pulsed inductive microwave magnetometer (PIMM) techniques were used to measure the ferromagnetic resonance (FMR) linewidth for a series of Permalloy films with thicknesses of 50 and 100nm. The SL-FMR measurements were made for fixed frequencies from 1.5to5.5GHz. The VNA-FMR and PIMM measurements were made for fixed in-plane fields from 1.6to8kA∕m (20–100Oe). The results provide a confirmation, lacking until now, that the linewidths measured by these three methods are consistent and compatible. In the field format, the linewidths are a linear function of frequency, with a slope that corresponds to a nominal Landau-Lifshitz phenomenological damping parameter α value of 0.007 and zero frequency intercepts in the 160–320A∕m (2–4Oe) range. In the frequency format, the corresponding linewidth versus frequency response shows a weak upward curvature at the lowest measurement frequencies and a leveling off at high frequencies.

/pdf/ferromagnetic-resonance-linewidth-in-metallic-thin-films-4nmku8h46u.pdf

Ferromagnetic resonance linewidth in metallic thin films: Comparison of measurement methods | NIST

The electrical manipulation of magnetization and exchange bias in antiferromagnet/ferromagnet thin films could be of use in the development of the next generation of spintronic devices. Current-controlled magnetization switching can be driven by spin–orbit torques generated in an adjacent heavy-metal layer, but these structures are difficult to integrate with exchange bias switching and tunnelling magnetoresistance measurements. Here, we report the current-induced switching of the exchange bias field in a perpendicularly magnetized IrMn/CoFeB bilayer structure using a spin–orbit torque generated in the antiferromagnetic IrMn layer. By manipulating the current direction and amplitude, independent and repeatable switching of the magnetization and exchange bias field below the blocking temperature can be achieved. The critical current density for the exchange bias switching is found to be larger than that for CoFeB magnetization reversal. X-ray magnetic circular dichroism, polarized neutron reflectometry measurements and micromagnetic simulations show that a small net magnetization within the IrMn interface plays a crucial role in these phenomena. The magnetization and exchange bias field in an IrMn/CoFeB bilayer can be independently switched using a current-controlled spin–orbit torque generated in the antiferromagnetic IrMn layer.

Exchange bias switching in an antiferromagnet/ferromagnet bilayer driven by spin–orbit torque

In-plane magnetic anisotropy and coercive field dependence upon thickness of CoFeB

The competition between the interface crystallization and diffusion processes, their influence on the onset of symmetry-filtering coherent tunneling of ${\ensuremath{\Delta}}_{1}$ band electrons in the MgO-based magnetic tunnel junctions is investigated. Systematic study of the transport and magnetoresistance during thermal annealing of these junctions shows a unique behavior of the tunneling conductance in the parallel state. The optimal annealing time for achieving giant tunneling magnetoresistance at different temperatures is determined. The evolution of magnetoresistance consists of three distinct regions, responsible by different contributions from CoFeB electrodes and the MgO barrier. The whole phenomenon can be understood through an empirical model based on the Landauer tunneling picture.

Understanding tunneling magnetoresistance during thermal annealing in MgO-based junctions with CoFeB electrodes

Effects of composition, thickness and temperature on the magnetic properties of amorphous CoFeB thin films

This letter reports specular and diffuse x-ray reflectance studies of the interface in the ion beam sputtered CoFeB(∼5–8 nm)/MgO(∼2–5 nm) bilayers. The study reveals the specific roles of oxygen ion energy, substrate temperature, and reactive gas ambient on controlling the interface width in the bilayers. Depending on oxidation-method employed for MgO growth the interface width varies between 0.51 and 0.20 nm. Energy of assist ions (≤50 eV) plays a key role compared to the growth temperature in determining the sharpness of the interface. The bottom grown CoFeB exhibited significant increase in coercivity (HC), which also depends on MgO-growth process.

X-ray reflectance studies of interface in ion beam sputtered CoFeB/MgO bilayers

Electronic structure of magnetic Fe/MgO/Fe/Co multilayer structure by NEXAFS spectroscopy

Unconventional multi-jump magnetization reversal and significant in-plane uniaxial magnetic anisotropy (UMA) in the ion-beam sputtered amorphous Co20Fe60B20(5–75 nm) thin films grown on Si/amorphous SiO2 are reported. While such multi-jump behavior is observed in CoFeB(10 nm) film when the magnetic field is applied at 10°–20° away from the easy-axis, the same is observed in CoFeB(12.5 nm) film when the magnetic field is 45°–55° away from easy-axis. Unlike the previous reports of multi-jump switching in epitaxial films, their observance in the present case of amorphous CoFeB is remarkable. This multi-jump switching is found to disappear when the films are crystallized by annealing at 420 °C. The deposition geometry and the energy of the sputtered species appear to intrinsically induce a kind of bond orientation anisotropy in the films, which leads to the UMA in the as-grown amorphous CoFeB films. Exploitation of such multi-jump switching in amorphous CoFeB thin films could be of technological significance because of their applications in spintronic devices.

M. Raju

Papers

In-plane magnetic anisotropy and coercive field dependence upon thickness of CoFeB

X-ray reflectance studies of interface in ion beam sputtered CoFeB/MgO bilayers

Electronic structure of magnetic Fe/MgO/Fe/Co multilayer structure by NEXAFS spectroscopy

Multi-jump magnetic switching in ion-beam sputtered amorphous Co20Fe60B20 thin films

Effect of interface on magnetic properties of Co20Fe60B20 in ion-beam sputtered Si/CoFeB/MgO and Si/MgO/CoFeB bilayers