.
\nJust as electronics revolutionized computing and communications technology,
\nspintronics is touted to follow suit. This relatively new field involves manipulating
\nthe flow of a magnetism-related property called \u2018spin\u2019. In magnons, a spintronic
\n counterpart of electrons, Naoto Nagaosa from the RIKEN Institute and his colleagues
\n have observed an effect first seen with electrons over 130 years ago: the Hall effect.
\n The Hall effect is used in sensitive detectors, so the researchers believe their finding
\n could lead to new applications for magnetic insulators.
\n.
\nThe Hall effect arises because a charge-carrying particle such as an electron experiences
\na force perpendicular to its direction of motion as it moves through a magnetic field of a
\nconducting material. The result is a build-up of charges of opposite signs on either side
\nof the material, which creates a measureable electric field. Magnons, however, have no
\n charge, so an analogous effect had never been observed previously.
\n.
\n\u201cThe Hall effect is one of the most fundamental phenomena in condensed matter physics,\u201d
\n explains Nagaosa. \u201cIt is important to study to what extent we can apply ideas from conventional
\n electronics to spintronics.\u201d Nagaosa, along with Yoshinori Tokura also from ASI, Yoshinori
\nOnose and co-workers from The University of Tokyo, and Hosho Katsura from the University
\nof California, Santa Barbara, USA, studied the magnetic and thermal properties of the
\n insulating ferromagnet Lu2V2O7 at low temperatures. Rather than the electric field
\nassociated with the conventional effect, the Hall effect manifested in this material as a
\nthermal conductivity gradient across the sample. This difference occurs because the
\nmagnons carry heat, rather than charge.
\n.
\nThe researchers showed that the size of the effect is not proportional to the applied
\n magnetic field, but has a maximum at relatively low fields. This supports the hypothesis
\n that magnons, influenced by the relativistic interaction, are responsible because the
\nnumber of magnons is known to be reduced at these low-level magnetic fields. They
\nalso observed that the conductivity gradient started to decrease at higher fields.
\nThis observation allowed Nagaosa and colleagues to rule out lattice vibrations,
\nor phonons, as another possible underlying cause of the experimental results:
\na phonon-induced thermal conductivity gradient would be expected to continue
\n to increase with magnetic field.
\n.
\n\u201cAccording to our theoretical prediction, only certain types of the crystal structure
\n show this magnon Hall effect,\u201d says Nagaosa. \u201cTo confirm this theory, we next
\naim to check that the phenomenon is absent in more conventional structures
\nsuch as a cubic lattice.\u201d
\n.<\/p>\n","protected":false},"excerpt":{"rendered":"
. Just as electronics revolutionized computing and communications technology, spintronics is touted to follow suit. This relatively new field involves manipulating the flow of a magnetism-related property called \u2018spin\u2019. In magnons, a spintronic counterpart of electrons, Naoto Nagaosa from the RIKEN Institute and his colleagues have observed an effect first seen with electrons over 130 … <\/p>\n