Magnetic domain and domain-wall imaging of submicron Co dots by probing the magnetostrictive response using atomic force microscopy

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.An approach to image the domains and domain walls of small ferromagnetic entities using atomic force microscopy(AFM), with a nonmagnetic AFM probe, has been developed. Exciting the sample in an external acmagnetic field, the distribution of magnetostrictive response at the surface is detected. By this technique, the domains and domain walls of submicron Co dots have been imaged with a 1 nm lateral resolution. In elliptical Co dots with a 350-nm-long axis on a triangular lattice array with 400 nm periodicity, we find evidence for two domains with opposite magnetization orientation across a wall. The domain-wall width in these dots is found to be about 35 nm. Furthermore, we observe a ferromagnetic alignment of the domains in the neighboring dots, which suggests a magnetostatic interaction among the dots

Hysteresis and Fractional Matching in Thin Nb Films with Rectangular Arrays of Nanoscaled Magnetic Dots

We have investigated the periodic pinning of magnetic flux quanta in thin Nb films with rectangular arrays of magnetic dots. In this type of pinning geometry, a change in the periodicity and shape of the minima in the magnetoresistance occurs for magnetic fields exceeding a certain threshold value. This has been explained recently in terms of a reconfiguration transition of the vortex lattice due to an increasing vortex-vortex interaction with increasing magnetic field. In this picture the dominating elastic energy at high fields forces the vortex lattice to form a square symmetry rather than being commensurate to the rectangular geometry of the pinning array. In this paper we present a comparative study of rectangular arrays with Ni-dots, Co-dots and holes. In the magnetic dot arrays, we found a strong fractional matching effect up to the second order matching field. In contrast, no clear fractional matching is seen after the reconfiguration. Additionally, we discovered the existence of hysteresis in the magnetoresistance in the crossover between the low and the high field regime. We found evidence that this effect is correlated to the reconfiguration phenomenon rather than to the magnetic state of the dots. The temperature and angular dependences of the effect have been measured and possible models are discussed to explain this behavior.Comment: 1 Table, 5 Figure

Terahertz near-field nanoscopy of mobile carriers in single semiconductor nanodevices

We introduce ultraresolving terahertz (THz) near-field microscopy based on THz scattering at atomic force microscope tips. Nanoscale resolution is achieved by THz field confinement at the very tip apex to within 30 nm, which is in good agreement with full electro-dynamic calculations. Imaging semiconductor transistors, we provide first evidence of 40 nm (λ/3000) spatial resolution at 2.54 THz (wavelength λ = 118 μm) and demonstrate the simultaneous THz recognition of materials and mobile carriers in a single nanodevice. Fundamentally important, we find that the mobile carrier contrast can be directly related to near-field excitation of THz-plasmons in the doped semiconductor regions. This opens the door to quantitative studies of local carrier concentration and mobility at the nanometer scale. The THz near-field response is extraordinary sensitive, providing contrast from less than 100 mobile electrons in the probed volume. Future improvements could allow for THz characterization of even single electrons or biomolecules.Financially supported by BMBF within the NanoFutur program, Grant 03N8705, Deutsche Forschungsgemeinschaft Clusters of Excellence “Nanosystems Initiative Munich (NIM)” and “Munich-Centre for Advanced Photonics (MAP)”, and Etortek project from the Government of the Basque Country. Angela Collantes (Infineon) is acknowledged for TEM imaging.Peer reviewe

Slow relaxation of the polarization in pulsed laser ablated highly oriented ferroelectric thin films

The relaxation of the polarization (as determined by the pyroelectric effect) of high quality laser ablated films of PbZr0.52Ti0.48O3 has been measured after saturation with an applied electric field. The decay is observed to be quasilogrithmic over four decades in time. Analysis of measurements of the remanent polarization and the depolarization remanence are consistent with the depolarization field providing a polarization-state-dependent field of the correct direction to drive the decay. Also, the quasilogrithmic time dependence is consistent with a model for slow relaxation or creep with the depolarization field the driving field for the decay.These observations along with our AFM measurements imply that for maximum polarization stability a ferroelectric film should consist of decoupled grains. The optimum grain size should be the maximum grain size which does not support domain walls

Magnetic domain and domain-wall imaging of submicron Co dots by probing the magnetostrictive response using atomic force microscopy

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.An approach to image the domains and domain walls of small ferromagnetic entities using atomic force microscopy(AFM), with a nonmagnetic AFM probe, has been developed. Exciting the sample in an external acmagnetic field, the distribution of magnetostrictive response at the surface is detected. By this technique, the domains and domain walls of submicron Co dots have been imaged with a 1 nm lateral resolution. In elliptical Co dots with a 350-nm-long axis on a triangular lattice array with 400 nm periodicity, we find evidence for two domains with opposite magnetization orientation across a wall. The domain-wall width in these dots is found to be about 35 nm. Furthermore, we observe a ferromagnetic alignment of the domains in the neighboring dots, which suggests a magnetostatic interaction among the dots