A Scanning Hall Probe Microscope for High Resolution milliKelvin Magnetic Imaging
Lead Research Organisation:
University of Bath
Department Name: Physics
Abstract
Some of the most exciting contemporary problems in condensed matter physics are in the area of nanoscale quantum mechanics and relate to the properties of superconducting and ferromagnetic materials at ultra-low temperatures, e.g. in the study of macroscopic quantum tunnelling and novel forms of quantum order. A key aspect of this work is the ability to perform high spatial resolution magnetic imaging down to ultra-low temperatures and/or at high magnetic fields. Due to the major technical challenges posed in these regimes, no magnetic imaging system currently exists which is capable of nanoscale imaging. Over the last decade we have successfully developed a number of scanning Hall probe microscopes (SHPMs) in Bath which span the temperature range 4.2-300K. These Hall probe systems represent a very flexible approach to magnetic imaging since Hall sensors can readily be fabricated with ~100nm spatial resolution and excellent minimum detectable fields and, using high probe current densities, can be operated in magnetic fields of several Teslas. All existing SHPM systems use 4He exchange gas cooling and, hence, can only be operated above 4.2K. In order to address a range of exciting contemporary problems in magnetic materials at much lower temperatures we propose to design and construct a new SHPM head which can be directly attached to the 300mK cold pot of a commercial 3He cryostat insert. This instrument will be capable of operation in magnetic fields up to 10T with a spatial resolution >100nm and minimum detectable field ~10mG/Hz^0.5. Its unique properties will be exploited to open up a new front in the field of nanoscale quantum phenomena. Within the project we will search for novel vortex structures and spontaneously generated flux in the unconventional superconductor Sr2RuO4, and will attempt to establish the mechanism for macroscopic quantum tunnelling of the magnetisation in the molecular magnet Mn12-acetate. In addition we will search for new geometry-driven vortex structures in mesoscopic Al disks.
Publications
Curran PJ
(2015)
Spontaneous symmetry breaking in vortex systems with two repulsive lengthscales.
in Scientific reports
Curran P
(2014)
Search for spontaneous edge currents and vortex imaging in Sr 2 Ru O 4 mesostructures
in Physical Review B
Mohammed H
(2014)
Fabrication of nanoscale Bi Hall sensors by lift-off techniques for applications in scanning probe microscopy
in Semiconductor Science and Technology
Lukyanchuk I
(2014)
Rayleigh instability of confined vortex droplets in critical superconductors
in Nature Physics
Bending S
(2012)
Vortex imaging in unconventional superconductors
in Physica C: Superconductivity
Desoky W
(2012)
Multiband superconductivity in Co-doped SrFe 2 As 2 investigated using local magnetic imaging
in Superconductor Science and Technology
Curran P
(2011)
Vortex imaging and vortex lattice transitions in superconducting Sr 2 RuO 4 single crystals
in Physical Review B
Crisan A
(2011)
Intermittent trapping of a liquid-like vortex state visualized by scanning Hall probe microscopy
in Superconductor Science and Technology
Curran P
(2010)
Geometry-dependent penetration fields in superconducting Bi 2 Sr 2 CaCu 2 O 8 + d platelets
in Physical Review B
Bending S
(2010)
Scanning Hall probe microscopy of vortex matter
in Physica C: Superconductivity
Connolly M
(2010)
Continuum versus discrete flux behaviour in large mesoscopic Bi2Sr2CaCu2O8+d disks
in Physica C: Superconductivity and its Applications
Bending S
(2009)
Scanning Hall Probe Imaging of Nanoscale Magnetic Structures
in Sensor Letters
Connolly M
(2009)
Continuum vs . discrete flux behaviour in large mesoscopic Bi 2 Sr 2 CaCu 2 O 8+d disks
in EPL (Europhysics Letters)
Connolly M
(2009)
Vortex 'puddles' and magic vortex numbers in mesoscopic superconducting disks
in Journal of Physics: Conference Series
Bending S
(2009)
Vortex-antivortex 'molecular crystals' in hybrid ferromagnet/superconductor structures
in Journal of Physics: Conference Series
Khotkevych V
(2009)
A milliKelvin scanning Hall probe microscope for high resolution magnetic imaging
in Journal of Physics: Conference Series
Connolly M
(2008)
Magneto-optical imaging of flux penetration into arrays of Bi 2 Sr 2 CaCu 2 O 8 microdisks
in Physical Review B
Crisan A
(2008)
Manipulation of pancake vortices by rotating a Josephson vortex lattice
in Superconductor Science and Technology
Bending S
(2008)
Competing symmetries in superconducting vortex-antivortex "molecular crystals"
in Physica C: Superconductivity and its Applications
Khotkevych VV
(2008)
A scanning Hall probe microscope for high resolution magnetic imaging down to 300 mK.
in The Review of scientific instruments
Neal J
(2007)
Competing Symmetries and Broken Bonds in Superconducting Vortex-Antivortex Molecular Crystals
in Physical Review Letters
Albrecht J
(2007)
Inhomogeneous vortex distribution and magnetic coupling in oxide superconductor-ferromagnet hybrids
in New Journal of Physics
Description | We have found no evidence for spontaneous generated flux in Sr2RuO4 single crystals due to the presence of a chiral order parameter. However we have observed a structural vortex lattice transition from triangular at very low fields to square at higher fields which was previously theoretically predicted. More recently we have been studying mesoscopic disk structures milled into the surface of an Sr2RuO4 single crystal. We find that the vortex pinning in these disks abruptly collapses at an applied field of ~25Oe suggesting a possible field-driven change in the order parameter. We have observed a remarkable symmetry breaking in the structure of vortex patterns in MgB2 thin films. This may be linked to the two-band nature of superconductivity in MgB2, though one would not expect this to be important in the rather disordered thin films studied. We have studied flux structures in OsB2 single crystals which was thought to be a type I compound superconductor, though our sample was almost certainly type II. Finally we have made provisional investigations of geometry-driven flux patterns in Al mesostructures. |
Exploitation Route | This is basic underpinning research and is being disseminated to the worldwide academic community via presentations and lectures at international institutions and conferences. |
Sectors | Electronics Energy |
Description | The project has led to an application note P13 with Attocube who manufactured the 3-axis nanopositioning stage used in our milliKelvin scanning Hall probe microscope. This is generating new business for the company. |
First Year Of Impact | 2008 |
Sector | Manufacturing, including Industrial Biotechology |
Impact Types | Economic |
Description | Iowa State University |
Organisation | Iowa State University |
Country | United States |
Sector | Academic/University |
Start Year | 2006 |
Description | University of Antwerp |
Organisation | Antwerp University Hospital |
Country | Belgium |
Sector | Hospitals |
PI Contribution | Performed experiments in mesoscopic superconductivity. |
Collaborator Contribution | Milorad Milosevic performed Ginzburg-Landau and analytic calculations to understand our experiments. |
Impact | Single discipline collaboration. |
Start Year | 2006 |
Description | University of Leeds |
Organisation | University of Leeds |
Country | United Kingdom |
Sector | Academic/University |
Start Year | 2006 |
Description | University of St Andrews |
Organisation | University of St Andrews |
Country | United Kingdom |
Sector | Academic/University |
Start Year | 2006 |
Description | University of Tokyo |
Organisation | University of Tokyo |
Country | Japan |
Sector | Academic/University |
Start Year | 2006 |