[Show abstract][Hide abstract] ABSTRACT: In this paper the magnetic field detection limits of microscopic Hall sensors are investigated as a function of their lateral size. Hall sensors fabricated from GaAs/AlGaAs heterostructures and silicon are experimentally investigated at different temperatures using Hall effect and noise spectrum measurements. At room temperature a clear size dependence of the detection limit is observed, whereas at low temperatures this dependence is found to disappear. The results are explained using the theory of noise in semiconductors.
Full-text · Article · Aug 2009 · The Review of scientific instruments
[Show abstract][Hide abstract] ABSTRACT: Ballistic Hall magnetometry is used to investigate the magnetization of a mesoscopic superconducting Pb square as a function of magnetic field (H) and temperature (T). Vortex penetration and expulsion fields are determined from magnetization curves at different temperatures below Tc and are combined in an experimental T-H phase diagram. Enhanced stability of the symmetry-matching vorticities L=1 and L=4 is observed. The experimental results are compared with theoretical calculations using the nonlinear Ginzburg-Landau theory for a thin square.
No preview · Article · Nov 2007 · Physical review. B, Condensed matter
[Show abstract][Hide abstract] ABSTRACT: The effect of the patterning of a Ga1-xMnxAs (x=0.08) film into an array of microscopic dots on its magnetic properties is locally studied by means of scanning Hall probe microscopy. The measured stray field patterns indicate the presence of a single domain state with a uniform magnetization within the Ga1-xMnxAs dots. The magnetic anisotropy of the dot array is directly imaged, revealing a  easy axis in the as-grown sample and a  easy axis orientation after annealing. In contrast to a temperature dependent anisotropy in the plain Ga1-xMnxAs film, no magnetic easy axis reorientation is observed within the experimentally accessible temperature range.
Full-text · Article · Nov 2006 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: Inhomogeneous magnetic fields generated by the
BaFe12O19 ferromagnetic substrate create a
magnetic template for superconducting condensate in the
Nb/BaFe12O19 hybrids. Depending on the field and
temperature, the magnetic template guides superconductivity to nucleate
in different areas: above the magnetic domain walls of the
BaFe12O19 forming the domain-wall
superconductivity (DWS), above the reversed magnetic domains (RDS), and
above the positive magnetic domains forming bulk superconductivity. The
DWS, behaving as a superconducting wire network, survives in a broad
field range. The RDS, existing in the form of isolated superconducting
islands near the saturation field Hs of
BaFe12O19 , can be described as a two-dimensional
two-component random conductor mixture. Being related to the hysteretic
domain evolution, superconducting condensate above the reversed domains
shows pronounced switching behavior.
No preview · Article · Jun 2006 · Physical Review B