R. I. Miller

Evidence for static magnetism in the vortex cores of ortho-II YBa2Cu3O6.50.

Evidence for static alternating magnetic fields in the vortex cores of underdoped YBa2Cu3O6+x is reported. Muon spin rotation measurements of the internal magnetic field distribution of the vortex state of YBa2Cu3O6.50 in applied fields of H = 1 T and H = 4 T reveal a feature in the high-field tail of the field distribution which is not present in optimally doped YBa2Cu3O6.95 and which fits well to a model with static magnetic fields in the vortex cores. The magnitude of the fields is estimated to be 18(2) G and decreases above T = 10 K. We discuss possible origins of the additional vortex core magnetism within the context of existing theories.

Field Induced Reduction of the Low-Temperature Superfluid Density in YBa{sub 2}Cu{sub 3}O{sub 6.95}

A novel high magnetic field (8 T) spectrometer for muon spin rotation has been used to measure the temperature dependence of the in-plane magnetic penetration depth {lambda}{sub ab} in YBa{sub 2}Cu {sub 3}O{sub 6.95} . At low H and low T , {lambda}{sub ab} exhibits the characteristic linear T dependence associated with the energy gap of a d{sub x{sup 2}-y{sup 2}}-wave superconductor. However, at higher fields {lambda}{sub ab} is essentially temperature independent at low T . We discuss possible interpretations of this surprising new feature in the low-energy excitation spectrum. (c) 1999 The American Physical Society.

Local magnetic properties of a monolayer of Mn12 single molecule magnets.

The magnetic properties of a monolayer of Mn12 single molecule magnets grafted onto a silicon (Si) substrate have been investigated using depth-controlled beta-detected nuclear magnetic resonance. A low-energy beam of spin-polarized radioactive 8Li was used to probe the local static magnetic field distribution near the Mn12 monolayer in the Si substrate. The resonance line width varies strongly as a function of implantation depth as a result of the magnetic dipolar fields generated by the Mn12 electronic magnetic moments. The temperature dependence of the line width indicates that the magnetic properties of the Mn12 moments in this low-dimensional configuration differ from bulk Mn12.

Near-Surface Structural Phase Transition of SrTiO~3 Studied with Zero-Field beta-Detected Nuclear Spin Relaxation and Resonance

We demonstrate that zero-field beta-detected nuclear quadrupole resonance and spin relaxation of low energy (8)Li can be used as a sensitive local probe of structural phase transitions near a surface. We find that the transition near the surface of a SrTiO(3) single crystal occurs at T(c) approximately 150K, i.e., approximately 45K higher than T(c)bulk, and that the tetragonal domains formed below T(c) are randomly oriented.

Muon-Spin Rotation Measurements of the Magnetic Field Dependence of the Vortex-Core Radius and Magnetic Penetration Depth in NbSe{sub 2}

Muon-spin rotation spectroscopy ({mu}SR) has been used to measure the internal magnetic field distribution in NbSe{sub 2} for H{sub c1}{lt}H{lt}0.25H{sub c2} . The deduced profiles of the supercurrent density J{sub s} indicate that the vortex-core radius {rho}{sub 0} in the bulk decreases sharply with increasing magnetic field. This effect, which is attributed to increased vortex-vortex interactions, does not agree with the dirty-limit microscopic theory. A simple phenomenological equation in which {rho}{sub 0} depends on the intervortex spacing is used to model this behavior. In addition, we find for the first time that the in-plane magnetic penetration depth {lambda}{sub ab} increases linearly with H in the vortex state of a conventional superconductor. {copyright} {ital 1997} {ital The American Physical Society}

Low-energy spin-polarized radioactive beams as a nano-scale probe of matter

Abstract We have commissioned a polarized low-energy 8 Li ion beam line, which together with a high-field β-NMR spectrometer, can act as sensitive new probe of thin films and interfaces. The implantation energy can be continuously adjusted from 1 to 90 keV and the maximum polarization achieved thus far is 80%. This instrument opens up new applications for β-NMR which parallel and complement efforts with low-energy muons. For example, it is possible to probe the magnetic field distribution near the surface of a material by stopping a polarized 8 Li beam in a thin overlayer of Ag. Since the 8 Li adopts a site with cubic symmetry in Ag there is no quadrupolar splitting of the resonance, and the 8 Li acts as a purely magnetic sensor.

Magnetic-field effects on the size of vortices below the surface of NbSe2 detected using low energy beta-NMR.

A low energy radioactive beam of polarized

MEASUREMENT OF THE FUNDAMENTAL LENGTH SCALES IN THE VORTEX STATE OF YBA2CU3O6.60

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Correlations between charge ordering and local magnetic fields in overdoped YBa2Cu3O6+x

Li has been used to observe the vortex lattice near the surface of superconducting NbSe

Superconductivity and field-induced magnetism in Pr2-xCexCuO4 single crystals

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