Effects of high pressure, magnetic fields, and substitutions - ICMR ...

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Ferroelectricity in Multiferroics with E-Type Magnetic Order (Theory – Double exchange model) E-type magnetic order in RMnO 3 : Sergienko/Dagotto, PRL 2006: R = Ho “Double-exchange” (virtual) mechanism works against Jahn-Teller distortion in FM spin chains along a-axis Does not involve DM interaction Large FE polarization predicted Problems: Experimental – only polycrystalline samples can be synthesized (high-pressure synthesis) Theoretical – predicted polarization is three orders of magnitude larger than measured Dual nature of FE (electronic + ionic) recently suggested (Picozzi et al., PRL 2007) P (μC/m 2 ) a ΔE ~ - t 2 /δ cosΦ Mn-O-Mn 15 10 5 b P T NC 0 0 10 20 30 T (K) T L H=0 5 kOe 15 kOe 20 kOe 25 kOe 35 kOe Pbnm
2. Magnetoelastic effects and spin-lattice coupling – how to measure these effects ? In multiferroics the spin-lattice interaction plays a decisive role in mediating the (improper) ferroelectricity induced by magnetic orders The measurements of the ionic displacements and/or the macroscopic lattice strain is therefore of interest Scattering experiments (x-ray, neutron) provide the tool to measure displacements on a microscopic level – but often lack the resolution to detect the tiny changes. Note: The atomic displacements explaining the experimental values of the FE polarization are as small as 10 -4 Å. Only a few attempts to derive structural distortions at the magnetic and ferroelectric transitions in multiferroics have been successful.
Page 1 and 2: Tuning multiferroics under extreme
Page 3 and 4: 1. Short introduction: Multiferroic
Page 5 and 6: 2. Frustration due to competing int
Page 7 and 8: Novel physical effects in multiferr
Page 9 and 10: 2. Helical magnetic order, exchange
Page 11 and 12: WMnO 4 Frustration due to competing
Page 13 and 14: Symmetry and Landau theory (Kenzelm
Page 15: Ferroelectricity due to possible ex
Page 20 and 21: Structural distortions in multiferr
Page 22 and 23: Dielectric Anomaly at and below T N
Page 24 and 25: Strong spin-spin and spin-lattice c
Page 26 and 27: Search for structural anomalies at
Page 28 and 29: 3. The effects of high pressure on
Page 30 and 31: Be-Cu cap with wires, sample, and p
Page 32 and 33: Pressure - temperature phase diagra
Page 34 and 35: Pressure effects on magnetic struct
Page 36 and 37: Control of magnetic order (commensu
Page 38 and 39: Complex p - T phase diagram of DyMn
Page 40 and 41: In multiferroics with a paraelectri
Page 42 and 43: Understanding the pressure effects
Page 44 and 45: Chapon et al. (PRL 2006) explained
Page 46 and 47: Example 1: WMnO 4 In MnWO 4 the Mn
Page 48 and 49: Example 2: CuFeO 2 T. Kimura et al.

Effects of high pressure, magnetic fields, and substitutions - ICMR ...

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