Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session V2a: Frustrated Quantum Magnetism |
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Sponsoring Units: DCMP GMAG Chair: Arthur Ramirez, Lucent Tech, Bell Labs Room: LACC 151 |
Thursday, March 24, 2005 11:15AM - 11:51AM |
V2a.00001: Heisenberg antiferromagnet on the pyrochlore lattice Invited Speaker: The Heisenberg antiferromagnet on the network of corner-sharing tetrahedra (the ``pyrochlore lattice'') is arguably the world's most frustrated system: the classical version of this magnet has a ground state with an extensive entropy and shows no sign of magnetic order in numerical simulations [1]. A real-life incarnation of this model is found in ZnCr$_2$O$_4$, which exhibits several peculiar effects traceable to the strong frustration: a spin-Peierls-like phase transition [2], a strongly correlated paramagnetic state with zero modes [3], and a magnetization plateau in high magnetic fields [4]. I will review recent theoretical and experimental developments in this area of research. \newline \newline [1] R. Moessner and J. T. Chalker, Phys. Rev. B {\bf 58,} 12049 (1998).\newline [2] S.-H. Lee {\em et al.}, Phys. Rev. Lett. {\bf 84,} 3718 (2000).\newline [3] S.-H. Lee {\em et al.}, Nature {\bf 418,} 856 (2002); cond-mat/0208587. [4] K. Penc, N. Shannon, and H. Shiba, Phys. Rev. Lett. {\bf 93,} 197203 (2004). [Preview Abstract] |
Thursday, March 24, 2005 11:51AM - 12:27PM |
V2a.00002: Cobaltates:Superconductivity in the triangular lattice tJ model Invited Speaker: The newly found sodium cobaltates provide a new and exciting challenge in the study of correlated matter in condensed matter physics. There appears to be a greater hope of ultimate resolution than in the case of high Temperature superconductors due to drastically smaller a Fermi temperature scale here. Electronic frustration ( i.e. a dependence on the sign of electron tunneling amplitude) occurs along with spin frustration on the triangular lattice that underlies these compounds. I review some key experiments, and discuss the ongoing and evolving modeling of these systems. I discuss some theoretical results for the transport properties, particularly the Hall constant. [Preview Abstract] |
Thursday, March 24, 2005 12:27PM - 1:03PM |
V2a.00003: Magnetically induced ferroelectric order in frustrated magnets Invited Speaker: Magnetoelectric coupling between magnetic and ferroelectric properties has been the object of intense study over the last four decades. Our understanding of magnetoelectric materials has been greatly enhanced by a rigorous exploration of the symmetry requirements for promoting magnetic and ferroelectric orders. Multiferroic materials, having simultaneous magnetic and ferroelectric order, have recently been proposed for incorporation into a range of spintronic devices. However, many of the multiferroics identified to date have different transition temperatures for ferroelectric and magnetic orders, leading to reduced magnetoelectric coupling strengths. I will discuss some recent experiments on several new multiferroics, including TbMnO$_3$, DyMnO$_3$, and Ni$_3$V$_2$O$_8$. These compounds are notable because the ferroelectric transition is coincident with magnetic ordering which leads to very large magnetoelectric couplings and large magnetocapacitive effects. Furthermore, using external magnetic fields to tune the magnetic structure has a pronounced effect on ferroelectricity in these systems. This allows us to destroy or promote ferroelectric order magnetically. While similar effects have been observed previously, these multiferroics remain poorly understood. I will present a model developed to explain the multiferroic order in Ni$_3$V$_2$O$_8$, in which the magnetic order spontaneously breaks inversion symmetry, allowing for the development of ferroelectricity. This magnetically-induced ferroelectric order is expected to appear in a wide range of antiferromagnets, and offers a new approach for designing and understanding multiferroic materials. [Preview Abstract] |
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