ferromagnetic resonance

Introduction

Ferromagnetic resonance (FMR) is a powerful technique used to study the magnetic properties of ferromagnetic materials. It involves the resonant absorption of microwave radiation by the magnetic moments in a material, providing insights into various magnetic parameters such as anisotropy, damping, and spin dynamics. This synthesis explores recent advancements and methodologies in FMR, particularly focusing on nanoscale applications and the influence of electric fields and spin-transfer torques.

Key Insights

Nanoscale Ferromagnetic Resonance Techniques:
- FMR can be induced in individual nanoscale samples using an oscillating electric current at microwave frequencies, allowing characterization of materials with uniform magnetization profiles .
- Spin-transfer-driven FMR enables measurements of magnetic excitations in nanoscale ferromagnets, providing detailed information about exchange, damping, and spin-transfer torques.
Electric Field Influence on FMR:
- Electric fields can be used to control FMR excitations, potentially reducing power consumption in spintronic devices.
- The precessing magnetization in a ferromagnet/normal-metal/ferromagnet structure can rectify alternating currents, generating a dc voltage, which is influenced by electric fields.
Spin-Orbit Coupling and Structural Effects:
- Spin-orbit coupling and structural inversion asymmetry play significant roles in the FMR of nanoscale bars, affecting resonant damping and anisotropy.
Voltage Generation via FMR:
- FMR can generate a dc voltage at a normal-metal contact to a ferromagnet due to spin-flip scattering and spin dynamics in the nonmagnetic region.
Physical Conditions and Resonance Modes:
- Various resonance modes can be excited in ferromagnetic wires, influenced by factors such as wire radius, microwave magnetic field symmetry, and skin depth.
- The resonance fields of bulk samples follow Kittel’s resonance condition, while nanowires exhibit distinct resonance modes due to their smaller radius.
Historical and Material-Specific Studies:
- Early discoveries and experiments on FMR have provided foundational knowledge, including studies on metals and alloys of the iron and lanthanide groups.
- Specific materials like CrBr3 and single-crystal samples of nickel and iron have been studied for their unique FMR properties, such as linewidths and anisotropy .

Conclusion

Ferromagnetic resonance remains a crucial technique for understanding the magnetic properties of materials, with significant advancements in nanoscale applications and electric field control. The ability to induce and measure FMR in individual nanoscale samples, coupled with the influence of spin-orbit coupling and structural effects, opens new avenues for research and technological applications in spintronics. Additionally, the generation of dc voltage through FMR and the exploration of various resonance modes in different materials highlight the diverse potential of this technique.

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Ferromagnetic resonance

Summary

Introduction

Key Insights

Conclusion

Sources and full results

Spin-orbit-driven ferromagnetic resonance.

This study introduces a new form of ferromagnetic resonance that allows for the characterization of individual nanoscale samples with uniform magnetization profiles, using microwave frequencies to create an effective magnetic field.

Electric-field-induced ferromagnetic resonance excitation in an ultrathin ferromagnetic metal layer

Electric fields can control ferromagnetic resonance excitations in ultrathin metal layers, potentially reducing power consumption in spintronic devices and systems.

Spin-transfer-driven ferromagnetic resonance of individual nanomagnets.

This study demonstrates a technique for measuring ferromagnetic resonance in individual nanomagnets, providing detailed information on exchange, damping, and spin-transfer torques in magnetic nanostructures.

Physical conditions for ferromagnetic resonance

All but one of the multiple ferromagnetic resonances observed in a sphere correspond to modes in which the oscillating part of the magnetization is independent of r or varies linearly with r in the sample.

Theory of the spin-torque-driven ferromagnetic resonance in a ferromagnet/normal-metal/ferromagnet structure

Current-driven ferromagnetic resonance in a ferromagnet/normal-metal/ferromagnet tri-layer can generate a dc voltage, with a second mechanism contributing equally for thin ferromagnetic films.

Voltage generation by ferromagnetic resonance at a nonmagnet to ferromagnet contact.

Ferromagnettic resonance can generate a DC voltage at a nonmagnet to ferromagnet contact, allowing time-dependent magnetization sensing using established dc electronic techniques.

Ferromagnetic resonance in microwires and nanowires

Ferromagnetic resonance in thin ferromagnetic wires can be characterized by two modes: the main resonance for a thin planar plate and the weak "insulator" mode for nanowires.

Ferromagnetic resonance at the Clarendon Laboratory, Oxford. A tribute to J. H. E. Griffiths (1908–1981)

Ferromagnetic resonance was discovered in 1945 by J. H. E. Griffiths at the Clarendon Laboratory, and his research on metals and alloys has shaped our understanding of transition elements and their alloys.

Ferromagnetic Resonance in CrBr3

Ferromagnetic resonance in CrBr3 crystals at 1.5°K reveals a narrow linewidth of 3.5 oe, with a g value of 2.006 and uniaxial anisotropy of 9.4 105 ergs/cm3.

Ferromagnetic Resonance in Nickel and Iron

Ferromagnetic resonance linewidths in nickel and iron are mainly due to exchange-conductivity broadening, with relaxation damping and exchange-conductivity mechanisms contributing to nickel results.

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