[Host: Seung-Hun Lee ]
Geometrical frustration gives rise to a large number of degenerate ground states and suppresses a simple-minded long-range ordering in general. Here we discuss theoretically how the degeneracy is lifted in three-dimensionally frustrated pyrochlore systems whose lattice structure consists of corner-sharing tetrahedra. The pyrochlore systems are most typically found in the so-called B spinel oxides. Focusing on the spinels
with B=V and Cr, we explore the low-temperature physics by the mean-field argument and Monte Carlo simulation for effective spin-orbital-lattice coupled models.
For V spinels, we clarify the strong interplay between spin and orbital degrees of freedom.
Orbital ordering reduces the magnetic frustration partially and realizes weakly coupled
one-dimensional chains in the three-dimensional pyrochlore lattice. For Cr spinels,
we show that the system exhibits novel phase transitions under the external magnetic
field due to the spin-Peierls type mechanism. An emergence of a half-magnetization
plateau is discussed in detail.
Condensed Matter Seminar
Thursday, March 17, 2005
Physics Building, Room 204
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