267 research outputs found
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
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 of the applied
field.Comment: 4 page
Magnetization and EPR studies of the single molecule magnet Ni with integrated sensors
Integrated magnetic sensors that allow simultaneous EPR and magnetization
measurements have been developed to study single molecule magnets. A high
frequency microstrip resonator has been integrated with a micro-Hall effect
magnetometer. EPR spectroscopy is used to determine the energy splitting
between the low lying spin-states of a Ni single crystal, with an S=4
ground state, as a function of applied fields, both longitudinal and transverse
to the easy axis at 0.4 K. Concurrent magnetization measurements show changes
in spin-population associated with microwave absorption. Such studies enable
determination of the energy relaxation time of the spin system.Comment: 4 pages, 4 figures, accepted for publication (Proceedings of the 10th
Joint MMM/Intermag Conference, which will be published as special issues of
the Journal of Applied Physics
Magnetic resonance spectroscopy of perpendicularly magnetized permalloy multilayer disks
Using a Magnetic Resonance Force Microscope, we compare the ferromagnetic
resonance spectra of individual micron-size disks with identical diameter, 1
m, but different layer structures. For a disk composed of a single 43.3 nm
thick permalloy (Py) layer, the lowest energy mode in the perpendicular
configuration is the uniform precession. The higher energy modes are standing
spin-waves confined along the diameter of the disk. For a Cu(30)/Py(100)/Cu(30)
nm multilayer structure, it has been interpreted that the lowest energy mode
becomes a precession localized at the Cu/Py interfaces. When the multilayer is
changed to Py(100)/Cu(10)/Py(10) nm, this localized mode of the thick layer is
coupled to the precession of the thin layer
A Frequency-Controlled Magnetic Vortex Memory
Using the ultra low damping NiMnSb half-Heusler alloy patterned into
vortex-state magnetic nano-dots, we demonstrate a new concept of non-volatile
memory controlled by the frequency. A perpendicular bias magnetic field is used
to split the frequency of the vortex core gyrotropic rotation into two distinct
frequencies, depending on the sign of the vortex core polarity inside
the dot. A magnetic resonance force microscope and microwave pulses applied at
one of these two resonant frequencies allow for local and deterministic
addressing of binary information (core polarity)
Dynamics of two coupled vortices in a spin valve nanopillar excited by spin transfer torque
We investigate the dynamics of two coupled vortices driven by spin transfer.
We are able to independently control with current and perpendicular field, and
to detect, the respective chiralities and polarities of the two vortices. For
current densities above , a highly coherent signal
(linewidth down to 46 kHz) can be observed, with a strong dependence on the
relative polarities of the vortices. It demonstrates the interest of using
coupled dynamics in order to increase the coherence of the microwave signal.
Emissions exhibit a linear frequency evolution with perpendicular field, with
coherence conserved even at zero magnetic field
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