Dirac Strings and Magnetic Monopoles in the Spin Ice Dy ₂ Ti ₂ O ₇

Abstract

Sources of magnetic fields-magnetic monopoles-have so far proven elusive as elementary particles. Condensed-matter physicists have recently proposed several scenarios of emergent quasiparticles resembling monopoles. A particularly simple proposition pertains to spin ice on the highly frustrated pyrochlore lattice. The spin-ice state is argued to be well described by networks of aligned dipoles resembling solenoidal tubes-classical, and observable, versions of a Dirac string. Where these tubes end, the resulting defects look like magnetic monopoles. We demonstrated, by diffuse neutron scattering, the presence of such strings in the spin ice dysprosium titanate (Dy2Ti2O7). This is achieved by applying a symmetry-breaking magnetic field with which we can manipulate the density and orientation of the strings. In turn, heat capacity is described by a gas of magnetic monopoles interacting via a magnetic Coulomb interaction.

A novel type of splayed ferromagnetic order observed in Yb2Ti2O7

“…It is characterized by dipolar correlations emerging from the topological spin-ice constraint. This translates into pinch-points in the neutron diffuse scattering patterns [11] and magnetic monopole excitations [12,13,14].Because of its large ground-state degeneracy, a spin-ice compound does not order magnetically, i.e., it is in a so-called spin liquid state where the spins are strongly correlated although they do not display long range order. Quantum fluctuations are not expected to play a significant role for Ho 2 Ti 2 O 7 .…”

Encoding Magnetic States in Monopole‐Like Configurations Using Superconducting Dots

“…Especially attractive are artificial monopole‐like defects because of their similarity to magnetic charges. They can be generated in spin ice materials or in the form of head‐to‐head domain walls in magnetic nanowires,5, 6, 7, 8, 9, 10, 11, 12 however controllable approaches to imprint and manipulate such spin structures are needed. Here we present a novel strategy for robustly encoding nontrivial magnetic states in artificial nanoscale hybrid systems, formed by a soft ferromagnetic (FM) thin film interacting with hard superconducting thin dots.…”

“…Geometrical frustration has been the main strategy to generate nontrivial, monopolar‐like defects and other exotic states in magnetic materials such as spin ice systems or magnetic nanowires 5, 6, 7, 8, 9, 10, 11, 12, 13, 14. Skyrmions and other topological structures are typically created by artificially adding extra interactions, such as Dzyaloshinskii–Moriya interaction,2 to the conventional magnetic energy.…”

Molecular Em Fields and Dynamical Responses in Solids With Magnetic Charges

“…Then the configuration suffers a change in such a way that the magnetic field sources are similar to those due to the existence of micromagnets with two poles, the denominated dumbbells [7,8,[10][11][12]19]. Then, each micromagnet can be considered as a pole-antipole pair which can be broken when the length of the string which form these pairs increases.…”

“…A contribution to the interpretation of these monopoles was carried out in 1938 by Jordan [2] and in 1974 Hooft [3] and Polyakov [4] introduced the magnetic monopole idea as a contribution to the second great unification of the three more intense forces, electromagnetic, weak nuclear and strong nuclear interactions. These and other theoretical analysis have provoked that the experimental pursuit of the magnetic monopole manifestation is an issue that is both liminal and subliminally present since 1982 [5] and now is receiving a payment of attention in both high energy physics [6] and solid state (SS) physics [6][7][8][9][10][11][12][13][14][15].…”