An aluminum coated tapered optical fiber is rigidly attached to one of the prongs of a high Q piezoelectric tuning fork. The fork is mechanically dithered at its resonance frequency (33 kHz) so that the tip amplitude does not exceed 0.4 nm. A corresponding piezoelectric signal is measured on electrodes appropriately placed on the prongs. As the tip approaches within 20 nm above the sample surface a 0.1 nN drag force acting on the tip causes the signal to reduce. This signal is used to position the optical fiber tip to about 0 to 25 nm above the sample. Shear forces resulting from the tip-sample interaction can be quantitatively deduced.

The electronic valence state of Mn in Pb(Zr0.2Ti0.8)O3/La0.8Sr0.2MnO3 multiferroic heterostructures is probed by near edge x-ray absorption spectroscopy as a function of the ferroelectric polarization. We observe a temperature independent shift in the absorption edge of Mn associated with a change in valency induced by charge carrier modulation in the La0.8Sr0.2MnO3, demonstrating the electronic origin of the magnetoelectric effect. Spectroscopic, magnetic, and electric characterization shows that the large magnetoelectric response originates from a modified interfacial spin configuration, opening a new pathway to the electronic control of spin in complex oxide materials.PACS numbers: 75.70. Cn,78.70.Dm,73.90.+f,75.60.Ej,85.30.Tv,75.30.Kz,85.70.Ay Understanding how to couple the electric and magnetic order parameters in the solid state is a long-standing scientific challenge that is intimately linked to the spatial and temporal symmetries associated with charge and spin. Coupling of the order parameters is observed in many different materials, but the effect is generally weak in magnitude, even in materials that are both ferroelectric and ferromagnetic (multiferroic) [1][2][3]. Increasing the magnitude of the coupling is a fundamental problem in condensed matter physics with important implications for applications. For example, strong magnetoelectric coupling allows for the ultra-sensitive measurement of weak magnetic fields, and at smaller length scales, enables spin-based technologies by allowing the control of the spin state at the atomic scale via electric fields.In single phase multiferroics, the magnetic and ferroelectric orders often occur largely independent of each other, and as a result the magnetoelectric coupling tends to be small [2,4]. In order to overcome this intrinsic limitation in the coupling between the order parameters, artificially structured materials with enhanced magnetoelectric couplings have been engineered, where a break in time reversal and spatial symmetry occurs naturally at the interface between the different phases [3,5,6]. Moreover, the coupling mechanism can be tailored to benefit from several phenomena, including elastic [7,8], magnetic exchange bias [9][10][11], and charge-based [12] couplings. In charge-based multiferroic composites, the sensitivity of the electronic and spin state of strongly correlated oxides to charge provides enhanced coupling between magnetic and ferroelectric order parameters [12]; it often relies on charge doping of a "colossal" magnetoresistive (CMR) manganite to modulate between high and low spin states, which compete for the ground state of the system. However, the microscopic origin of this effect is still not fully understood. In particular, the nature of the effect and how the interplay between charge, spin, and valency combines to yield the large magnetoelectric response in this system remain to be addressed. In this Letter, we explore the sensitivity of x-ray absorption near edge spectroscopy (XANES) to the atomic electronic state to demons...

Reflection scanning near-field optical microscopy with uncoated fiber tips: How good is the resolution really?

Comment on "A nanopositioner for scanning probe microscopy: The KoalaDrive" [Rev. Sci. Instrum. 83, 023703 (2012)] Rev. Sci. Instrum. 83, 097101 (2012) Three-axis correction of distortion due to positional drift in scanning probe microscopy Rev. Sci. Instrum. 83, 083711 (2012) A near-field scanning microwave microscope for characterization of inhomogeneous photovoltaics Rev. Sci. Instrum. 83, 083702 (2012) Scanning gate microscopy on a graphene nanoribbon Appl. Phys. Lett. 101, 063101 (2012) Additional information on Rev. Sci. Instrum. This paper explores the fundamental limits of the use of quartz tuning forks as force detectors in scanned probe microscopy. It is demonstrated that at room temperature, pressure, and atmosphere these force sensors have a noise floor of 0.62 pN/ͱHz and exhibit a root mean square Brownian motion of only 0.32 pm. When operated as a shear force sensor both dissipative and reactive forces are detected on approach to the sample. These forces are sufficient to reduce the amplitude of motion of the probe nearly to zero without physically contacting the surface. It is also demonstrated that conventional proportional-integral feedback control yields closed loop responses at least 40 times faster than their open loop response.

Articles you may be interested inPrediction of giant magnetoelectric effect in LaMnO3/BaTiO3/SrMnO3 superlattice: The role of n-type SrMnO3/LaMnO3 interface J. Appl. Phys. 116, 074102 (2014); 10.1063/1.4893370 Enhanced magnetism and ferroelectricity in epitaxial Pb(Zr0.52Ti0.48)O3/CoFe2O4/La0.7Sr0.3MnO3 multiferroic heterostructures grown using dual-laser ablation technique Enhanced magnetoelectric effect in La0.67Sr0.33MnO3/PbZr0.52Ti0.48O3 multiferroic nanocomposite films with a SrRuO3 buffer layer Coexistence of tunneling magnetoresistance and electroresistance at room temperature in La0.7Sr0.3MnO3/(Ba, Sr)TiO3/La0.7Sr0.3MnO3 multiferroic tunnel junctions J. Appl. Phys. 109, 07D915 (2011); 10.1063/1.3564970 Control of magnetism in Pb(Zr0.2Ti0.8)O3/La0.8Sr0.2MnO3 multiferroic heterostructures (invited)The magnetoelectric response of Pb͑Zr 0.2 Ti 0.8 ͒O 3 / La 0.8 Sr 0.2 MnO 3 ͑PZT/LSMO͒ artificial multiferroic heterostructures as a function of temperature, electric, and magnetic field, shows that the largest magnetoelectric coupling is attained at temperatures near the magnetic critical point of LSMO, at ϳ180 K ͑−13.5 Oe cm kV −1 ͒. The magnetoelectric coupling displays a strong temperature dependence, changing sign at 150 K and saturating to positive values below ϳ100 K ͑+6 Oe cm kV −1 ͒. The magnetoelectric curve switches hysteretically between two states in response to the ferroelectric switching. The peak in the magnetoelectric response coincides with the observation of on/off switching of magnetism in LSMO near the critical region, where the sensitivity to electric field is largest, making it a promising approach for device applications.

We report a study of a gallium phosphide, hemispherical, solid immersion lens through the imaging of 40-nm-diam fluorescent dye balls. A spatial resolution as small as 139 nm has been achieved at a wavelength of 560 nm, which is equivalent to a diffraction-limited system of numerical aperture 2.0. This resolution is a 33% improvement over conventional oil immersion objectives and previously reported solid immersion lenses, which typically have a numerical aperture around 1.5.

We report the observation of a sharp absorption line in the photoluminescence excitation spectra of individual naturally occurring quantum dots in a narrow (2.8 nm) GaAs͞Al 0.3 Ga 0.7 As quantum well that is remarkably constant throughout the sample. We propose that it is identified as the delocalized two-dimensional exciton. This assignment is confirmed by photoluminescence and photoluminescence excitation diffusion experiments.

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