Charge Hopping in Glassy Magnets

Abstract

Viewpoint: Charge Hopping in Glassy Magnets Gavin Lawes, Department of Physics and Astronomy, Wayne State University, Detroit, MI 48201, USA Published March 19, 2012 | Physics 5, 35 (2012) | DOI: 10.1103/Physics.5.35 In some transition metal oxides, disorder makes the dielectric constant highly sensitive to an applied magnetic field over a broad range of temperatures. Near-Room-Temperature Colossal Magnetodielectricity and Multiglass Properties in Partially Disordered La2NiMnO6 D. Choudhury, P. Mandal, R. Mathieu, A. Hazarika, S. Rajan, A. Sundaresan, U. V. Waghmare, R. Knut, O. Karis, P. Nordblad, and D. D. Sarma Phys. Rev. Lett. 108, 127201 (2012) Published March 19, 2012 | PDF (free) +Enlarge image Figure 1 APS/Carin Cain Figure 1 Schematic illustration of the mechanism for magnetodielectric coupling in partially antisite-disordered La2NiMnO6. Green: La; Blue: Ni; Red: Mn; Gray: Bridging O. The gray arrows on the O ions represent the magnetic interactions between neighboring magnetic ions. Charge transfer between the Ni2+ and Mn4+ produces a large dipole moment in the unit cell, which is suppressed by the ferromagnetic spin alignment in an applied magnetic field. Magnetodielectric materials, which have a dielectric constant that is modulated by an applied magnetic field, provide rich insight into the physics of spin-charge coupling. The coupling between the dielectric constant and magnetic field—the magnetodieletric coupling—is often mediated by lattice dynamics [1], typically leading to only very small shifts in the dielectric constant. Some special classes of materials do exhibit exceptionally large shifts—a relative change in the dielectric constant of 500% in high magnetic fields [2]—but these effects are generally present only in a very narrow range of temperatures near a phase transition and are not suitable for robust device applications. Materials having a substantial magnetodielectric coupling at high temperatures are expected to lead to the development of novel devices, including capacitive magnetic field sensors and tunable high-frequency filters [3, 4]. One of the outstanding challenges in the study of magnetodiectrics is to identify mechanisms that can lead to strong spin-charge coupling, with the goal of producing large magnetically induced shifts in the dielectric response over a wide temperature range encompassing room temperature.