Detection of localized ferromagnetic resonance in a continuous thin film via magnetic resonance force microscopy (original) (raw)
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We present Magnetic Resonance Force Microscopy (MRFM) measurements of Ferromagnetic Resonance (FMR) in a 50 nm thick permalloy film, tilted with respect to the direction of the external magnetic field. At small probe-sample distances the MRFM spectrum breaks up into multiple modes, which we identify as local ferromagnetic resonances confined by the magnetic field of the MRFM tip. Micromagnetic simulations support this identification of the modes and show they are stabilized in the region where the dipolar tip field has a component anti-parallel to the applied field.
Perturbation of magnetostatic modes observed by ferromagnetic resonance force microscopy
Physical Review B, 2006
Magnetostatic modes of yttrium iron garnet ͑YIG͒ films are investigated by ferromagnetic resonance force microscopy. A thin-film "probe" magnet at the tip of a compliant cantilever introduces a local inhomogeneity in the internal field of the YIG sample. This influences the shape of the sample's magnetostatic modes, thereby measurably perturbing the strength of the force coupled to the cantilever. We present a theoretical model that explains these observations; it shows that the tip-induced variation of the internal field creates either a local "potential barrier" or "potential well" for the magnetostatic waves. The data and model together indicate that local magnetic imaging of ferromagnets is possible, even in the presence of long-range spin coupling, through the introduction of localized magnetostatic modes predicted to arise from sufficiently strong tip fields.
Ferromagnetic resonance force spectroscopy of individual submicron-size samples
Physical Review B, 2008
We review how a magnetic resonance force microscope (MRFM) can be applied to perform ferromagnetic resonance (FMR) spectroscopy of individual sub-micron size samples. We restrict our attention to a thorough study of the spin-wave eigen-modes excited in permalloy (Py) disks patterned out of the same 43.3 nm thin film. The disks have a diameter of either 1.0 or 0.5 µm and are quasi-saturated by a perpendicularly applied magnetic field. It is shown that quantitative spectroscopic information can be extracted from the MRFM measurements. In particular, the data are extensively compared with complementary approximate models of the dynamical susceptibility: i) a 2D analytical model, which assumes an homogeneous magnetization dynamics along the thickness and ii) a full 3D micromagnetic simulation, which assumes an homogeneous magnetization dynamics below a characteristic length scale c and which approximates the cylindrical sample volume by a discretized representation with regular cubic mesh of lateral size c = 3.9 nm. In our analysis, the distortions due to a breaking of the axial symmetry are taken into account, both models incorporating the possibility of a small misalignment between the applied field and the normal of the disks.
Ferromagnetic resonance force microscopy on a thin permalloy film
Applied Physics Letters, 2007
Ferromagnetic Resonance Force Microscopy (FMRFM) offers a means of performing local ferromagnetic resonance. We have studied the evolution of the FMRFM force spectra in a continuous 50 nm thick permalloy film as a function of probe-film distance and performed numerical simulations of the intensity of the FMRFM probe-film interaction force, accounting for the presence of the localized strongly nonuniform magnetic field of the FMRFM probe magnet. Excellent agreement between the experimental data and the simulation results provides insight into the mechanism of FMR mode excitation in an FMRFM experiment.
NMR Spectroscopy for Thin Films by Magnetic Resonance Force Microscopy
Scientific Reports, 2013
Nuclear magnetic resonance (NMR) is a fundamental research tool that is widely used in many fields. Despite its powerful applications, unfortunately the low sensitivity of conventional NMR makes it difficult to study thin film or nano-sized samples. In this work, we report the first NMR spectrum obtained from general thin films by using magnetic resonance force microscopy (MRFM). To minimize the amount of imaging information inevitably mixed into the signal when a gradient field is used, we adopted a large magnet with a flat end with a diameter of 336 mm that generates a homogeneous field on the sample plane and a field gradient in a direction perpendicular to the plane. Cyclic adiabatic inversion was used in conjunction with periodic phase inversion of the frequency shift to maximize the SNR. In this way, we obtained the 19 F NMR spectrum for a 34 nm-thick CaF 2 thin film. N MR is a very powerful research tool used as widely as X-ray in physics, chemistry, biology, medicine and engineering. It may not be an accident that X-ray CT and MRI, which are the two most frequently used fundamental diagnosis tools in hospitals, are based on X-ray and NMR, respectively. The signal obtained from NMR basically contains all information on the local electronic and nuclear states. In physics, mostly the interaction between nuclei and electrons is analyzed to get the state and dynamics of electrons in condensed matters. In chemistry and biology, typically the interaction among nuclei is used to get molecular structure. Since a nuclear spin is adopted as a probe in NMR, measurement hardly disturbs the physical state of a sample under investigation. This noninvasive probing capability is best utilized in imaging. NMR was also the first tool to demonstrate quantum computing. It is difficult to imagine that quantum control of a single quantum state, which is one of the ultimate goals of nanotechnology, can be reached without magnetic resonance. The combination of capabilities to select nuclei, and observe static and dynamic interactions is still generating new applications in various fields.
Ferromagnetic Resonance Studies in Magnetic Nanosystems
Magnetochemistry
Ferromagnetic resonance is a powerful method for the study of all classes of magnetic materials. The experimental technique has been used for many decades and is based on the excitation of a magnetic spin system via a microwave (or rf) field. While earlier methods were based on the use of a microwave spectrometer, more recent developments have seen the widespread use of the vector network analyzer (VNA), which provides a more versatile measurement system at almost comparable sensitivity. While the former is based on a fixed frequency of excitation, the VNA enables frequency-dependent measurements, allowing more in-depth analysis. We have applied this technique to the study of nanostructured thin films or nanodots and coupled magnetic layer systems comprised of exchange-coupled ferromagnetic layers with in-plane and perpendicular magnetic anisotropies. In the first system, we have investigated the magnetization dynamics in Co/Ag bilayers and nanodots. In the second system, we have st...
Local field loop measurements by magnetic force microscopy
Journal of Physics D: Applied Physics, 2014
Magnetic force microscopy (MFM) is a valuable technique to investigate the reversal mechanisms of the magnetization in micrometric and sub-micrometric-patterned thin films that cannot be studied by means of magneto-optical methods because of their limited resolution. However, acquiring tens or hundreds of images consecutively at different applied magnetic fields is often impossible or impractical. Therefore, a field-dependent MFM-derived technique is discussed and applied on square and circular dots of different materials (Ni 80 Fe 20 , Co 67 Fe 4 Si 14.5 B 14.5 , Fe 78 Si 9 B 13 ) having sizes ranging from 800 nm to 20 µm. Experimental local hysteresis loops are obtained by properly analysing the phase signal of the MFM along a selected profile of the studied patterned structure, as a function of the applied magnetic field. Characteristic features of the magnetization process, such as vortex nucleation and expulsion, transition from C-state to saturated state or domain wall motion in Landau-like domain configuration are identified, and their evolution with the applied field is followed. The necessity to combine experimental and theoretical analyses is addressed by micromagnetic simulations on a model system (a Ni 80 Fe 20 square dot with a lateral size of 800 nm), comparable to one of the studied samples. The agreement between experimental and simulated MFM maps, at different applied fields, and hysteresis loops provides the necessary validation for the technique. Additionally, the simulations have been proven to be necessary to understand the magnetization reversal processes occurring in the studied sub-micrometric structures and to associate them with characteristic features of the hysteresis loops measured with the proposed technique.