Mechanical detection of nuclear spin relaxation in a micron-size crystal

A room temperature nuclear magnetic resonance force microscope (MRFM), fitted in a $^1$Tesla electromagnet, is used to measure the nuclear spin relaxation of $^1$H in a micron-size (70ng) crystal of ammonium sulfate. NMR sequences, combining both pulsed and continuous wave r.f. fields, have allowed us to measure mechanically $T_2$ and $T_1$, the transverse and longitudinal spin relaxation times. Because two spin species with different $T_1$ values are measured in our $7\mu{\rm m}$ thick crystal, magnetic resonance imaging of their spatial distribution inside the sample section are performed. To understand quantitatively the measured signal, we carefully study the influence of the spin-lattice relaxation and the non-adiabaticity of the c.w. sequence on the intensity and time dependence of the detected signal.Comment: latex drafteps.tex, 13 files, 12 pages [SPEC-S00/010], submitted to Eur. Phys. J.

Influence of parental compliance on the effectiveness of treatment of chronic gastroduodenal pathology in children

The article focuses on the studies which point to particular difficulties in achieving compliance in pediatrics. A dangerous trend to escalate the number and doses of antibiotics in anti- Helicobacter pylori (HP) schemes, the dosage frequency and course duration of eradication therapy considerably complicates a patient’s compliance to the treatment and contributes to a further growth of HP antibiotic resistance. In the treatment of children, the control of the outpatient therapy largely depends on the patient’s parent

Spectroscopy of the parametric magnons excited by 4-wave process

Using a Magnetic Resonace Force Microscope, we have performed ferromagnetic resonance (FMR) spectroscopy on parametric magnons created by 4-wave process. This is achieved by measuring the differential response to a small source modulation superimposed to a constant excitation power that drives the dynamics in the saturation regime of the transverse component. By sweeping the applied field, we observe abrupt readjustement of the total number of magnons each time the excitation coincides with a parametric mode. This gives rise to ultra-narrow peaks whose linewith is lower than $5~10^{-6}$ of the applied field.Comment: 4 page

Quantitative MRFM characterization of the autonomous and forced dynamics in a spin transfer nano-oscillator

Using a magnetic resonance force microscope (MRFM), the power emitted by a spin transfer nano-oscillator consisting of a normally magnetized Py$|$Cu$|$Py circular nanopillar is measured both in the autonomous and forced regimes. From the power behavior in the subcritical region of the autonomous dynamics, one obtains a quantitative measurement of the threshold current and of the noise level. Their field dependence directly yields both the spin torque efficiency acting on the thin layer and the nature of the mode which first auto-oscillates: the lowest energy, spatially most uniform spin-wave mode. From the MRFM behavior in the forced dynamics, it is then demonstrated that in order to phase-lock this auto-oscillating mode, the external source must have the same spatial symmetry as the mode profile, i.e., a uniform microwave field must be used rather than a microwave current flowing through the nanopillar

Magnetic resonance studies of the fundamental spin-wave modes in individual submicron Cu/NiFe/Cu perpendicularly magnetized disks

Spin wave spectra of perpendicularly magnetized disks with trilayers consisting of a 100 nm permalloy (Py) layer sandwiched by two Cu layers of 30 nm, are measured individually with a Magnetic Resonance Force Microscope (MRFM). It is demonstrated by 3D micromagnetic simulations that in disks having sub-micron size diameters, the lowest energy spin wave mode of the saturated state is not spatially uniform but rather is localized at the center of the Py/Cu interface in the region of a minimum demagnetizing field

Complete mapping of the spin-wave spectrum in vortex state nano-disk

We report a study on the complete spin-wave spectrum inside a vortex state nano-disk. Transformation of this spectrum is continuously monitored as the nano-disk becomes gradually magnetized by a perpendicular magnetic field and encouters a second order phase transition to the uniformly magnetized state. This reveals the bijective relationship that exists between the eigen-modes in the vortex state with the ones in the saturated state. It is found that the gyrotropic mode can be continuously viewed as a uniform phase precession, which uniquely softens (its frequency vanishes) at the saturation field to transform above into the Kittel mode. By contrast the other spin-wave modes remain finite as a function of the applied field while their character is altered by level anti-crossing

Comparative Measurements of Inverse Spin Hall and Magnetoresistance in YIG|Pt and YIG|Ta

We report on a comparative study of spin Hall related effects and magnetoresistance in YIG|Pt and YIG|Ta bilayers. These combined measurements allow to estimate the characteristic transport parameters of both Pt and Ta layers juxtaposed to YIG: the spin mixing conductance $G_{\uparrow \downarrow}$ at the YIG$|$normal metal interface, the spin Hall angle $\Theta_{SH}$, and the spin diffusion length $\lambda_{sd}$ in the normal metal. The inverse spin Hall voltages generated in Pt and Ta by the pure spin current pumped from YIG excited at resonance confirm the opposite signs of spin Hall angles in these two materials. Moreover, from the dependence of the inverse spin Hall voltage on the Ta thickness, we extract the spin diffusion length in Ta, found to be $\lambda_{sd}^\text{Ta}=1.8\pm0.7$ nm. Both the YIG|Pt and YIG|Ta systems display a similar variation of resistance upon magnetic field orientation, which can be explained in the recently developed framework of spin Hall magnetoresistance.Comment: 8 pages, 5 figures, 1 tabl

Detection of the microwave spin pumping using the inverse spin Hall effect

We report electrical detection of the dynamical part of the spin pumping current emitted during ferromagnetic resonance (FMR) using the inverse Spin Hall Effect (ISHE). The experiment is performed on a YIG$|$Pt bilayer. The choice of YIG, a magnetic insulator, ensures that no charge current flows between the two layers and only pure spin current produced by the magnetization dynamics are transferred into the adjacent strong spin-orbit Pt layer via spin pumping. To avoid measuring the parasitic eddy currents induced at the frequency of the microwave source, a resonance at half the frequency is induced using parametric excitation in the parallel geometry. Triggering this nonlinear effect allows to directly detect on a spectrum analyzer the microwave component of the ISHE voltage. Signals as large as 30 $\mu$V are measured for precession angles of a couple of degrees. This direct detection provides a novel efficient means to study magnetization dynamics on a very wide frequency range with great sensitivity

Mechanical magnetometry of Cobalt nanospheres deposited by focused electron beam at the tip of ultra-soft cantilevers

Using focused-electron-beam-induced deposition, Cobalt magnetic nanospheres with diameter ranging between 100 nm and 300 nm are grown at the tip of ultra-soft cantilevers. By monitoring the mechanical resonance frequency of the cantilever as a function of the applied magnetic field, the hysteresis curve of these individual nanospheres are measured. This enables to evaluate their saturation magnetization, found to be around 430 emu/cm^3 independently of the size of the particle, and to infer that the magnetic vortex state is the equilibrium configuration of these nanospheres at remanence