Head-to-head domain-wall phase diagram in mesoscopic ring magnets

Kläui, Mathias; Vaz, C. A. F.; Bland, J. A. C.; Heyderman, Laura J.; Nolting, F.; Pavlovska, A.; Bauer, E.; Cherifi, S.; Heun, S.; Locatelli, Andrea

doi:10.1063/1.1829800

Cited by 127 publications

(124 citation statements)

References 21 publications

Supporting

Mentioning

116

Contrasting

Unclassified

Order By: Relevance

“…The kagome geometry prevents the pathways crossing in a single switching transition. The conserved magnetic charge carriers have Q = ±2q and transverse domain walls are expected in our cobalt nanowires 20 Q = +2q defects (Q = +q, |M | = 2 m and Q = +3q, M = 0) are topologically equivalent and similarly the two Q = −2q defects, whereas at any given site we image a total magnetic charge Q = (±q ± 2q). On reversal of the magnetization in the array structure, the magnetic charge carrier is conserved and its motion down the dipole string is field directed and trackable, but monopole defects appear only when the magnetic charge carrier is trapped at a vertex site with like charge despite strong magnetic Coulomb's law repulsion.…”

Section: (R Ijmentioning

confidence: 99%

Direct observation of magnetic monopole defects in an artificial spin-ice system

et al. 2010

View full text Add to dashboard Cite

Free monopoles have fascinated and eluded researchers since their prediction by Dirac 1 in 1931. In spin ice, the bulk frustrated magnet, local ordering principles known as ice rules-two-in/two-out for four spins arranged in a tetrahedron-minimize magnetic charge. Remarkably, recent work 2-5 shows that mobile excitations, termed 'monopole defects', emerge when the ice rules break down 2 . Using a cobalt honeycomb nanostructure we study the two-dimensional planar analogue called kagome or artificial spin ice. Here we show direct images of kagome monopole defects and the flow of magnetic charge using magnetic force microscopy. We find the local magnetic charge distribution at each vertex of the honeycomb pins the magnetic charge carriers, and opposite charges hop in opposite directions in an applied field. The parameters that enter the problem of creating and imaging monopole defects can be mapped onto a simple model that requires only the ice-rule violation energy and distribution of switching fields of the individual bars of a cobalt honeycomb lattice. As we demonstrate, it is the exquisite interplay between these energy scales in the cobalt nanostructure that leads to our experimental observations.The dipolar interactions of a given spin with all of its nearest neighbours cannot be satisfied on a triangular lattice, resulting in a frustrated magnetic state with strong correlations and a local ordering principle, but no long-range order. Owing to its equivalence to the electrical charge distribution in water ice 6 , the materials are known as 'spin ices' and the local ordering scheme as the 'ice rules'. Spin-ice materials such as Dy 2 Ti 2 O 7 have been subject to an intense research effort 7,8 and frustrated magnetism has evolved into a deeply interdisciplinary field, providing model systems for complex biological problems and a mathematical basis for the neural network algorithm from the Sherrington-Kirkpatrick model 9 .A powerful way to understand spin ice is to consider the magnetic dipole as a positive and negative magnetic charge (±q) separated by one lattice spacing. The ice rule can then be described as the local minimization at each lattice site i of the total magnetic charge (Q i, = q i ). Predictions suggest that the magnetic properties can be fractionalized, with mobile excitations carrying magnetic charge, rather than spin, and their interactions being described by a magnetic Coulomb's law 2 (equation (1))where V 0 is the self-energy and r ij is the separation. Although these topological excitations are confined to the dipole lattice, and they are compatible with Maxwell's equations 10 , their free magnetic charge character has led to the nomenclature magnetic Blackett Laboratory, Imperial College, Prince Consort Road, London SW7 2AZ, UK. *e-mail: W.Branford@imperial.ac.uk.monopole defects. Recent studies 3-5,10 in rare-earth pyrochlores strongly suggest that monopole defects exist in bulk spin ice 10 .Creating an odd number of intersecting dipoles, as in 'kagome spin ice' 11 , is interesting becaus...

show abstract

Section: (R Ijmentioning

confidence: 99%

Direct observation of magnetic monopole defects in an artificial spin-ice system

et al. 2010

View full text Add to dashboard Cite

show abstract

“…Furthermore, the ability to control the structure of a domain wall through the geometrical dimensions of the magnetic wire allows the experimental study of fundamental physical properties of these different types of DWs. [9][10][11][12] Although there have been several experimental studies reporting the ability of artificially created constrictions to pin DWs, 10,[13][14][15] and numerous spin-transfer experiments currently use such artificial defects to precisely locate and hold DWs within magnetic nanostructures, 16,17 a complete understanding of how the local DW energy landscape is modified by artificial structural defects is currently lacking.…”

Section: Introductionmentioning

confidence: 99%

Mechanism for domain wall pinning and potential landscape modification by artificially patterned traps in ferromagnetic nanowires

et al. 2009

View full text Add to dashboard Cite

The interaction mechanism between transverse domain walls ͑TDWs͒ in Permalloy nanowires and artificially patterned traps is studied using high-sensitivity spatially resolved magneto-optical Kerr effect measurements and numerical simulations. T-shaped trap geometries are considered, where a DW traveling in the horizontal arm is pinned by the vertical arm. Pinning strengths as well as potential energy modifications created by the traps are measured, and the roles of the different DW characteristic parameters, such as the DW core orientation and the magnetic charge distribution within the DW, are presented. It is found that whether or not the core of the DW is aligned with the transverse arm of the T structure affects the shape of the main potential experienced by the DW, whereas the pinning strength strongly depends on which side of the V-shaped TDW interacts with the trap. The role of the magnetostatic interaction between the charge of the DW and the charge present at the junction is discussed.

show abstract

“…Here, all spins are aligned to the external field ͑schematically shown as A͒. Relaxing the field leads to the formation of highremanence onion states with transverse head-to-head domain walls 15 in the rings ͑B͒. At H y = −10 Oe, three small vortices nucleate at the three extremities of the tri-ring structure along the field direction, forming vortex head-to-head domain walls 15 ͑C͒.…”

Section: A Magneto-optical Kerr Effect and Simulationsmentioning

confidence: 99%

“…Relaxing the field leads to the formation of highremanence onion states with transverse head-to-head domain walls 15 in the rings ͑B͒. At H y = −10 Oe, three small vortices nucleate at the three extremities of the tri-ring structure along the field direction, forming vortex head-to-head domain walls 15 ͑C͒. With the increasing field, these small vortices start to move clockwise ͑in the top and bottom-left rings͒ and anticlockwise ͑bottom-right ring͒.…”

Section: A Magneto-optical Kerr Effect and Simulationsmentioning

confidence: 99%

“…Calculations of head-to-head domain wall structures in magnetic strips and rings predict either "transverse" walls with magnetization at the center of the wall directed transverse to the strip axis or "vortex" walls where the magnetization forms a small vortex at the center of the wall. 14,15 After removing the field, the onion state remains stable at remanence. 13 When a reverse field is applied, ideally both domain walls should move in the same direction around the ring.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Frustrated magnetic vortices in a triad of permalloy rings: Magneto-optical Kerr effect, magnetic force microscopy, and micromagnetic simulations

Rose

Buchanan

et al. 2006

Phys. Rev. B

View full text Add to dashboard Cite

The field dependent magnetization of three mutually touching permalloy rings were investigated by means of the magneto-optical Kerr effect, magnetic force microscopy, and micromagnetic simulations. Each ring has a width of 0.2-1.8 m, an outer diameter of 4 m, and a thickness of 17 nm. Decreasing an applied magnetic field from saturation leads to the nucleation and annihilation of magnetic vortices, leaving at least one ring in a magnetically frustrated state. The properties of the magnetization reversal strongly depend on the ring width and on the direction of the applied field. Multiple complex reversal paths with vortexlike magnetization configurations are found.

show abstract

Head-to-head domain-wall phase diagram in mesoscopic ring magnets

Cited by 127 publications

References 21 publications

Direct observation of magnetic monopole defects in an artificial spin-ice system

Direct observation of magnetic monopole defects in an artificial spin-ice system

Mechanism for domain wall pinning and potential landscape modification by artificially patterned traps in ferromagnetic nanowires

Frustrated magnetic vortices in a triad of permalloy rings: Magneto-optical Kerr effect, magnetic force microscopy, and micromagnetic simulations

Contact Info

Product

Resources

About