Vincent Castel

Spin-Hall magnetoresistance in platinum on yttrium iron garnet : Dependence on platinum thickness and in-plane/out-of-plane magnetization

The occurrence of spin-Hall magnetoresistance (SMR) in platinum (Pt) on top of yttrium iron garnet (YIG) has been investigated, for both in-plane and out-of-plane applied magnetic fields and for different Pt thicknesses [3, 4, 8, and 35 nm]. Our experiments show that the SMR signal directly depends on the in-plane and out-of-plane magnetization directions of the YIG. This confirms the theoretical description, where the SMR occurs due to the interplay of the spin-orbit interaction in the Pt and the spin-mixing conductance at the YIG/Pt interface. Additionally, the sensitivity of the SMR and spin pumping signals on the YIG/Pt interface conditions is shown by comparing two different deposition techniques (e-beam evaporation and dc sputtering).

Magnetoelectric effect in BaTiO3/Ni particulate nanocomposites at microwave frequencies

We present a comprehensive study of the magnetic and microwave properties of piezoelectric BaTiO3/magnetostrictive Ni nanocomposites (NCs), fabricated under uniaxial compression, at room temperature. In the current work, we investigated samples in the compositional range between 0≤fNi≤33.5 vol % and from 0.1 to 6 GHz using broadband microwave spectroscopy in combination with atomic and magnetic force microscopy (MFM), x-ray diffraction (XRD), electron transport, and broadband (6–28 GHz) ferromagnetic resonance (FMR) experiments in the microwave regime to correlate magnetization dynamics, electromagnetic materials parameters, and microstructural information. The static magnetic response is consistent with a model of a composite medium with an unmodified Ni phase in a nonmagnetic matrix. We provide the experimental evidence for a magnetoelectric (ME) effect, i.e., the effective permittivity at microwave frequencies can be controlled by an external magnetic field, which makes these nanostructures ready for m...

Platinum thickness dependence of the inverse spin-Hall voltage from spin pumping in a hybrid yttrium iron garnet/platinum system

We show the experimental observation of the platinum thickness dependence in a hybrid yttrium iron garnet/platinum system of the inverse spin-Hall effect from spin pumping, over a large frequency range and for different radio-frequency powers. From the measurement of the voltage at the resonant condition and the resistance of the normal metal layer, a strong enhancement of the ratio of these quantities has been observed, which is not in agreement with previous studies on the NiFe/platinum system. The origin of this behaviour cannot be fully explained by the spin transport model that we have used and is therefore still unclear.

Exchange magnetic field torques in YIG/Pt bilayers observed by the spin-Hall magnetoresistance

The effective field torque of an yttrium-iron-garnet (YIG) film on the spin accumulation in an attached platinum (Pt) film is measured by the spin-Hall magnetoresistance (SMR). As a result, the magnetization direction of a ferromagnetic insulating layer can be measured electrically. Experimental transverse and longitudinal resistances are well described by the theoretical model of SMR in terms of the direct and inverse spin-Hall effect, for different Pt thicknesses [3, 4, 8, and 35 nm]. Adopting a spin-Hall angle of Pt ?SH = 0.08, we obtain the spin diffusion length of Pt (? = 1.1±0.3?nm) as well as the real (Gr = (7±3)×1014???1m?2) and imaginary part (Gi = (5±3)×1013???1m?2) of the spin-mixing conductance and their ratio (Gr/Gi = 16±4).

Asymmetric magnetization reversal behavior in exchange-biased NiFe∕MnPt bilayers in two different anisotropy regimes: Close and far from critical thickness

The effect of the ratio between the uniaxial and unidirectional anisotropy on magnetization reversal in NiFe∕MnPt bilayers has been systematically studied using vectorial vibrating magnetometer. Depending on the balance between these two anisotropies the magnetization reverses either in the opposite or the same semicircles during the ascending and descending branches of the hysteresis loop. A simple modified coherent rotation model provides a good description of the magnetization reversal in these bilayers.

Controlled extrinsic magnetoelectric coupling in BaTiO3/Ni nanocomposites: Effect of compaction pressure on interfacial anisotropy

The dynamical control of the dielectric response in magnetoelectric (ME) nanocomposites (NCs) renders an entire additional degree of freedom to the functionality of miniaturized magnetoelectronics and spintronics devices. In composite materials, the ME effect is realized by using the concept of product properties. Through the investigation of the microwave properties of a series of BaTiO3/Ni NCs fabricated by compaction of nanopowders, we present experimental evidence that the compaction (uniaxial) pressure in the range 33–230 MPa affects significantly the ME features. The Ni loading was varied from zero (BaTiO3 only) to 63 vol %. Our findings revealed that the ME coupling coefficient exhibits a large enhancement for specific values of the Ni volume fraction and compaction pressure. The coupling effects in the NCs were studied by looking at the relationships among the crystallite orientation and the magnetic properties. The magnetization curves for different directions of the applied magnetic field cannot...

Broadband ferromagnetic resonance measurements in Ni/ZnO and Ni γ -Fe 2 O 3 nanocomposites

A comparative study at the ambient temperature of the ferromagnetic resonance (FMR) spectra of Ni/ZnO and Ni/γ-Fe2O3 nanocomposites (NCs) is reported. A microstrip transmission line technique was used to measure the FMR profiles and linewidths in the 8-24 GHz frequency range. The samples were placed at the center of a microstrip line where the derivative of the absorbed power was measured using a standard ac field modulation technique (10 Oe amplitude) and lock-in detection. The analysis of the FMR spectra can be interpreted as arising from aggregates of magnetic nanoparticles, each of which resonates in an effective magnetic field composed of the applied field, the average (magnetostatic) dipolar field, and the randomly oriented magnetic anisotropy field. It is found that frequency and applied magnetic field strongly influence the lineshape of the FMR spectra. Two observations are identified within the FMR spectra. On the one hand, the resonance field increased linearly with frequency as expected from uniform mode theory and yielded a Lande g factor in the range 1.48-2.05. On the other hand, there is no clear correlation between FMR linewidths and frequency. Inhomogeneity-based line-broadening mechanisms, due to the damping of surface/interface effects and interparticle interaction, affect the FMR effective linewidth.

Electromagnetomechanical coupling characteristics of plastoferrites

The impetus of this work was to investigate the electromagnetic and tensile properties of several commercially available plastoferrites (PFs) at ambient conditions. The approach involved selection of a set of PFs and measuring their complex effective permittivity e=e′−je″ and permeability μ=μ′−jμ″ under uniaxial stress at microwave frequencies (0.1–4.5GHz) and room temperature. We analyze the e and μ spectra for tensilely strained PFs up to 3%. Comparing our experimental e data against several dielectric relaxational behaviors, we find that the main physics cannot be understood with a single relaxation mechanism. We then go on to consider the magnetic permeability spectra in the microwave range of frequencies and show that an appropriate magnetization mechanism is given by the gyromagnetic spin resonance mechanism. We use a combination of Bruggeman mean field analysis and Landau-Lifshitz-Gilbert modeling to reproduce the experimental bimodal line-shape characteristics of the effective complex magnetic per...

Spin-wave resonances in exchange-coupled Permalloy/garnet bilayers

Exchange coupling at the interface between a single-crystal garnet film with a perpendicular anisotropy and a Permalloy film with an in-plane anisotropy was investigated both experimentally and theoretically. Wide-band (2–20 GHz) ferromagnetic resonance measurements in parallel configuration reveal spectra with multiple resonance lines (up to four). These data were analyzed by means of a standing spin-wave model extended to account for in-plane/out-of-plane anisotropy bilayers and to include a finite value of the bilinear interfacial exchange coupling J. The field and frequency evolutions of the observed multiple resonance peaks were satisfactorily reproduced using the value J=0.18±0.05 erg/cm2.

Thermal control of the magnon-photon coupling in a notch filter coupled to a yttrium iron garnet/platinum system

We report thermal control of mode hybridization between the ferromagnetic resonance and a planar resonator (notch filter) working at 4.74 GHz. The chosen magnetic material is a ferrimagnetic insulator (yttrium iron garnet: YIG) covered by 6 nm of platinum (Pt). A current-induced heating method has been used in order to enhance the temperature of the YIG/Pt system. The device permits us to control the transmission spectra and the magnon-photon coupling strength at room temperature. These experimental findings reveal a potentially applicable tunable microwave filtering function.