Synopsis: Unmasking the True Spin Relaxation Time

The experimental artifacts known to disrupt magnetic force microscopy measurements of small spin samples can be identified and removed.
Synopsis figure
Courtesy K. C. Fong/CalTech

In a typical electron spin resonance experiment, an ac magnetic field rotates the spins in a sample and induction electronics track their return to equilibrium. In comparison to this “classic” technique, magnetic resonance force microscopy (MFRM) is sensitive to a much smaller volume of spins—less than a hundred, in some cases. Instead of inductors, MFRMs measure the small change in oscillation frequency of a nanoscale magnetic tip as it is brought into contact with the molecular or atomic spins on a surface.

The so-called spin-lattice relaxation time—a measure of the spins’ interaction with their environment—can be extracted from these frequency shifts, which makes the technique useful for studying magnetic inhomogeneities in superconductors or spin qubits. But the measured spin relaxation time can vary with the power of the ac field or the distance between the oscillating tip and the surface. In a paper appearing in Physical Review B, Kin Chung Fong at the California Institute of Technology and his colleagues map out these effects in MRFM experiments, and show they can be removed to reveal the true local spin dynamics in a small ensemble of spins.

Fong et al. use a home-built MRFM to study spins localized at oxygen vacancies in silica. Their measurement probes a cubic volume 12 nanometers on a side, equivalent to a few hundred spins. Fong et al. achieve experimental conditions that allow their measurement to track the intrinsic spin-lattice relaxation time, suggesting the technique could study spin dynamics in other nanoscale materials. – Jessica Thomas


Features

More Features »

Announcements

More Announcements »

Subject Areas

Magnetism

Previous Synopsis

Particles and Fields

Gamma Rays Carry No Trace of Dark Matter

Read More »

Next Synopsis

Quantum Information

Superposed in a Crystal

Read More »

Related Articles

Synopsis: Sensing Earthly Magnetic Fields
Magnetism

Synopsis: Sensing Earthly Magnetic Fields

An organic material’s resistance changes measurably in weak magnetic fields, with a sensitivity similar to that of migrating birds. Read More »

Synopsis: Powering up Magnetization
Materials Science

Synopsis: Powering up Magnetization

New theoretical work identifies a dynamic form of multiferroic behavior, in which a time-varying electric polarization induces magnetization in a material. Read More »

Viewpoint: Closing in on a Magnetic Analog of Liquid Crystals
Condensed Matter Physics

Viewpoint: Closing in on a Magnetic Analog of Liquid Crystals

Nuclear magnetic resonance measurements strengthen the case that spins in a copper oxide exhibit nematic order similar to that found in liquid crystals. Read More »

More Articles