RELAXATION TIME MEASUREMT OF NITROXIDE PROBES FOR SCANNED-PROBE MAGNETIC FORCE

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. John Marohn has developed an approach that extends the applicability of ultrasensitive force gradient detection of magnetic resonance to samples with spin-lattice relaxation times (T1) as short as a single cantilever period. The generality of the approach, which relies on detecting either cantilever frequency or phase, was demonstrated by detecting electron spin resonance from a T1 = 1 ms nitroxide spin probe (TEMPAMINE) in a thin film at 4.2 K and 0.6 T. A custom fabricated cantilever with a 4 Mu m diameter nickel tip, was used to achieve a magnetic resonance sensitivity of 410 Bohr magnetons in a 1 Hz bandwidth. The theory underlying this experiment quantitatively predicts both the lineshape and the magnitude of the observed cantilever frequency shift as a function of field and cantilever-sample separation. The new approach has a number of advantages that make it well suited for magnetic resonance detection and imaging of nitroxide spin labels in an individual macromolecule at single-spin sensitivity