Dirac Strings and Magnetic Monopoles in the Spin Ice Dy2Ti2O7

• Published in: Science (American Association for the Advancement of Science) Vol. 326; no. 5951; pp. 411 - 414
• Main Authors: MORRIS, D. J. P, TENNANT, D. A, KIEFER, K, GERISCHER, S, SLOBINSKY, D, PERRY, R. S, GRIGERA, S. A, KLEMKE, B, CASTELNOVO, C, MOESSNER, R, CZTERNASTY, C, MEISSNER, M, RUIE, K. C, HOFFMANN, J.-U
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 16-10-2009; The American Association for the Advancement of Science
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Density; Exact sciences and technology; Ice; Magnetic fields; Magnetic properties and materials; Neutrons; Particle physics; Physics; Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.); Pyrochlore; Magnetization; Magnetic field effects; Spin ice; Coulomb interaction; Diffuse scattering; Neutron diffusion; Symmetry breaking; Specific heat; Magnetic monopoles; Quasiparticles; Dysprosium Titanates; Spin state; Exchange interactions
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1178868

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.