-4 -2 0 2 416.0

16.2

16.4

16.6

-10

0

10

20

b

E//[110]H//[1-11]

2 K 10 K 20 K 50 K 75 K 100 K 150 K

H (kOe)

2 K 10 K 20 K 50 K 75 K 100 K 150 K

a

Tb3Fe

5O

12

H//[1-11]

M ( B

mo

l-1)

Mesoscopic phase modulations

in complex materialsSang-W Cheong, Rutgers University

NSF-DMR-0405682

Intriguing cross-coupling phenomena in multiferroics where magnetism and ferroelectricity coexist. But, the spin/lattice coupling has always required large H/E. Recently, we found low-H spin/lattice coupling effect in Tb3Fe5O12.

Strain glass: a new state of matter phase-separated mixture of ferromagnetic-metallic phase and charge-ordered-insulating phase in CMR manganites undergoes a new type of collective phase transition, which is extremely sensitive on applied H.

  Ferroelectric and magnetic materials have been a time-honored subject of study and have led to some of the most important technological advances to date. Magnetism and ferroelectricity are involved with local spins and local dipoles (originating from off-center structural distortions), respectively. These two seemingly unrelated phenomena can coexist in certain unusual materials, termed multiferroics. Despite the possible coexistence of ferroelectricity and magnetism, a pronounced interplay between these properties has rarely been observed. This has prevented the realization of multiferroic devices offering such functionality. We have recently discovered extraordinary cross-coupling effects between spin and lattice degrees of freedom in a certain class of multiferroics. For example, we have found a highly reproducible electric polarization reversal in TbMn2O5 and an unprecedented large change of dielectric constant in DyMn2O5 that are both activated by an applied magnetic field. However, these intriguing phenomena occur only when high magnetic fields are applied, and thus are difficult to be exploited in real technological applications. We found that in the Tb3Fe5O12 garnet, dielectric constant changes significantly in low magnetic fields of about 1 kOe, which is technologically more practical.

Mixed-valent perovskite manganites show enormous magnetoresistance, which is coined as the colossal magnetoresistance (CMR) effect. It turns out that this CMR effect is closely associated with the phase separation tendency into microscopic metallic-ferromagnetic and insulating-charge-ordered regions. It has been speculated that the long-range strain associated with the large lattice change with charge/orbital ordering is directly responsible for the phase separation. We recently discovered that a manganite system with clear phase separated regions undergoes a collective phase transition at about 30 K, where all charge/spin/lattice degrees of freedom become collectively and randomly frozen. This unique ground state is called as “the strain glass state” in the sense that strain coupling plays the essential role in producing the collective random-freezing phenomenon.

Mesoscopic phase modulations

in complex materialsSang-W Cheong, Rutgers University

NSF-DMR-0405682

Education & inter-institutional collaboration.

High school students (N. Belakovski & Semmi Kim in the Partners in Science Program sponsored by the Liberty Science Center, New Jersey) have participated our research projects, and graduate students (Peng Gao and Yuhai Qing) at New Jersey Institute of Technologies (supervised by Trevor Tyson) are involved in collaborative experiments at Rutgers. In addition, we have continued our world-wide collaborations by the means of characterizing and discovering new properties of the materials, especially single crystals, synthesized in our lab.

Nickolai Belakovski, a high school student from Kimball Union Academy, is working on our PLD system with a Ph. D. graduate student, Nara Lee. They have deposited gate oxide films such as GGG or Al2O3 by using the PLD system. Right panel shows NbSe2 with a field effect transistor structure with a gate oxide.