Biomedical subjects

H J Mamin

Publications and source records attributed to H J Mamin.

7 recordsLinked to original sources

PubMed2005

Creating order from random fluctuations in small spin ensembles.

We demonstrate the ability to create spin order by using a magnetic resonance force microscope to harness the naturally occurring statistical fluctuations in small ensembles of electron spins. In one method, we hyperpolarized the spin system by selectively capturing the transient spin order created by the statistical fluctuations. In a second method, we took a more active approach and rectified the spin fluctuations by applying real-time feedback to the entire spin ensemble. The created spin order can be stored in the laboratory frame for a period on the order of the longitudinal relaxation time of 30 seconds and then read out.

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PubMed2004

Single spin detection by magnetic resonance force microscopy.

Magnetic resonance imaging (MRI) is well known as a powerful technique for visualizing subsurface structures with three-dimensional spatial resolution. Pushing the resolution below 1 micro m remains a major challenge, however, owing to the sensitivity limitations of conventional inductive detection techniques. Currently, the smallest volume elements in an image must contain at least 10(12) nuclear spins for MRI-based microscopy, or 10(7) electron spins for electron spin resonance microscopy. Magnetic resonance force microscopy (MRFM) was proposed as a means to improve detection sensitivity to the single-spin level, and thus enable three-dimensional imaging of macromolecules (for example, proteins) with atomic resolution. MRFM has also been proposed as a qubit readout device for spin-based quantum computers. Here we report the detection of an individual electron spin by MRFM. A spatial resolution of 25 nm in one dimension was obtained for an unpaired spin in silicon dioxide. The measured signal is consistent with a model in which the spin is aligned parallel or anti-parallel to the effective field, with a rotating-frame relaxation time of 760 ms. The long relaxation time suggests that the state of an individual spin can be monitored for extended periods of time, even while subjected to a complex set of manipulations that are part of the MRFM measurement protocol.

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PubMed2004

Suppression of spin diffusion near a micron-size ferromagnet.

We have used the large gradients generated near the ferromagnetic tip of a magnetic resonance force microscope to locally suppress spin diffusion in a silica sample containing paramagnetic electron spins. By controlling the slice location with respect to the tip, the magnetic field gradient was varied from 0.01 to 36 mT/microm, resulting in a fourfold decrease in T-11 and a similar decrease in T(-1)(1 rho). The observed dependence of the relaxation rates on field gradient is consistent with the quenching of flip-flop interactions that mediate the transport of magnetization between slow and fast relaxing spins.

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PubMed2003

Detection and manipulation of statistical polarization in small spin ensembles.

We report the detection of the square root of N statistical polarization in a small ensemble of electron spin centers in SiO2 by magnetic resonance force microscopy. A novel detection technique was employed that captures the statistical polarization and cycles it between states that are either locked or antilocked to the effective field in the rotating frame. Using field gradients as high as 5 G/nm, we achieved a detection sensitivity equivalent to roughly two electron spins, and observed ultralong spin-lock lifetimes, as long as 20 s. Given a sufficient signal-to-noise ratio, this scheme should be extendable to single electron spin detection.

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PubMed2001

Electron spin relaxation near a micron-size ferromagnet.

Magnetic resonance force microscopy was used to study the behavior of small ensembles of unpaired electron spins in silica near a micrometer-size ferromagnetic tip. Using a cantilever-driven spin manipulation protocol and a magnetic field gradient greater than 10(5) T/m, signals from as few as 100 net spins within a 20 nm thick resonant slice could be studied. A sixfold increase in the spin-lattice relaxation rate was found within 800 nm of the ferromagnet, while no effect due to silica surface proximity was detected. The results are interpreted in terms of Larmor-frequency magnetic field fluctuations emanating from the ferromagnet.

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PubMed2001

Noncontact friction and force fluctuations between closely spaced bodies.

Noncontact friction between a Au(111) surface and an ultrasensitive gold-coated cantilever was measured as a function of tip-sample spacing, temperature, and bias voltage using observations of cantilever damping and Brownian motion. The importance of the inhomogeneous contact potential is discussed and comparison is made to measurements over dielectric surfaces. Using the fluctuation-dissipation theorem, the force fluctuations are interpreted in terms of near-surface fluctuating electric fields interacting with static surface charge.

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PubMed2001

Magnetic dissipation and fluctuations in individual nanomagnets measured by ultrasensitive cantilever magnetometry.

Cantilever magnetometry with moment resolution better than 10(4)micro(B) was used to study individual nanomagnets. By using the fluctuation-dissipation theorem to interpret measurements of field-induced cantilever damping, the low frequency spectral density of magnetic fluctuations could be determined with resolution better than 1micro(B) Hz-1/2. Cobalt nanowires exhibited significant magnetic dissipation and the associated magnetic fluctuations were found to have 1/f frequency dependence. In individual submicron rare-earth alloy magnets, the dissipation/fluctuation was very small and not distinguishable from that of a bare silicon cantilever.

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