We report the observation of weak magnetism in superlattices of LaAlO(3)/SrTiO(3) using β-detected nuclear magnetic resonance. The spin lattice relaxation rate of ^{8}Li in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO(3) exhibits a strong peak near ~35 K, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the LaAlO(3)/SrTiO(3) interface. These results show that the magnetism at the interface depends strongly on the thickness of the spacer layer, and that a minimal thickness of ~4-6 unit cells is required for the appearance of magnetism. A simple model is used to determine that the observed relaxation is due to small fluctuating moments (~0.002μ(B)) in the two samples with a larger LaAlO(3) spacer thickness.

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.

A direct measurement of the London penetration depth in the high-T c superconductor YBa 2 Cu 3 O 6.92 has been made using low-energy SR with an effective background suppression method. The average magnetic field versus mean depth was measured in the Meissner state of high-purity detwinned crystals of YBa 2 Cu 3 O 6.92 . The resulting magnetic field profiles along the a and b axes are consistent with a local London model beyond 10 nm but there are deviations close to the surface. The absolute values of a and b extrapolated to zero temperature are 126.1Ϯ 1.2Ϯ 3 and 105.5Ϯ 1.0Ϯ 3 nm, respectively. These results are compared with other less direct methods and extend the use of low-energy SR to small crystals.One of the fundamental quantities of a superconductor is the London penetration depth, , which is the characteristic length scale that a magnetic field penetrates into the surface of a superconductor while in the Meissner state. 1 In the clean limit the absolute value of is directly related to the superfluid density n s via 1 / 2 = 0 e 2 n s / m and consequently its variation as a function of temperature, doping and orientation are of central importance in testing microscopic theories of exotic superconductors. For example, the linear variation in 1 / 2 with respect to temperature was a key finding confirming the d-wave nature of the pairing in YBa 2 Cu 3 O 6+x . 2,3 Also, early SR studies of the vortex phase in polycrystalline samples found a linear correlation between 1 / 2 and T c in the underdoped region. 4-6 More recent measurements on crystals both in the Meissner 7 and vortex states 8 indicate this systematic variation with doping is sublinear and may be connected with an approach to a quantum-critical point. 7,9 The large in-plane anisotropy of in YBa 2 Cu 3 O 6.95 measured with IR reflectivity, 10 was taken as evidence for a multiband effect, whereby a one-dimensional Fermi sheet associated with the CuO chains in YBa 2 Cu 3 O 6.95 contributes to the superfluid flowing in the chain direction. 11 This is a unique feature of YBa 2 Cu 3 O 6+x which distinguishes it from other cuprates. Accurate measurements of the absolute value of and its anisotropy are required to clarify central issues in YBa 2 Cu 3 O 6+x and more generally in the area of exotic superconductors.Unfortunately, accurate measurements of are difficult due to many possible systematic uncertainties. For example, in any bulk measurement the assumption of an exponential decay of the field in the Meissner state is only valid in the local London limit of a perfect surface. 1 This adds uncertainty to all bulk measurements where the field profile is assumed and not measured. Alternatively, one can determine from SR studies in the vortex state where the muon acts as a sensitive probe of the magnetic field distribution. 8,12,13 However, in this case the nonlocal and nonlinear effects complicate the theory 14 leading to an effective-fielddependent penetration depth. Until now there has been no way to verify to what extent this effective penetration de...

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.

We report the behavior of low energy 8 Li + implanted into gold as revealed by beta-detected NMR. At an external magnetic field of 3 T, two narrow resonances are observed, which are attributed to Li in the octahedral interstitial and the substitutional lattice sites. The Knight shifts for these two resonances are found to be temperature independent with values of +141͑4͒ and +73͑5͒ ppm, respectively. The spin-lattice relaxation rate in high magnetic fields at 290 K is slow, consistent with the Korringa relation; however, the rate increases dramatically for magnetic fields below about 2 mT. We attribute this to interaction of the 8 Li spin with the host lattice nuclear spins.

No abstract

No abstract

No abstract