Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Q36: Focus Session: Bulk Properties of Complex Oxides -- Fe-Based Multiferroics |
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Sponsoring Units: DMP GMAG Chair: Sang?Wook Cheong, Rutgers University Room: E146 |
Wednesday, March 17, 2010 11:15AM - 11:51AM |
Q36.00001: Ferroelectricity with Ferromagnetic Moment in Orthoferrites Invited Speaker: Exotic multiferroics with gigantic magnetoelectric (ME) coupling have recently been attracting broad interests from the viewpoints of both fundamental physics and possible technological application to next-generation spintronic devices. To attain a strong ME coupling, it would be preferable that the ferroelectric order is induced by the magnetic order. Nevertheless, the magnetically induced ferroelectric state with the spontaneous ferromagnetic moment is still quite rare apart from a few conical-spin multiferroics. To further explore multiferroic materials with both the strong ME coupling and spontaneous magnetization, we focused on materials with magnetic structures other than conical structure. In this talk we present that the most orthodox perovskite ferrite systems DyFeO$_{3}$ and GdFeO$_{3}$ have ``ferromagnetic-ferroelectric,'' i.e., genuinely multiferroic states in which weak ferromagnetic moment is induced by Dzyaloshinskii-Moriya interaction working on Fe spins and electric polarization originates from the striction due to symmetric exchange interaction between Fe and Dy (Gd) spins [1] [2]. Both materials showed large electric polarization ($>$0.1 $\mu $C/cm$^{2})$ and strong ME coupling. In addition, we succeeded in mutual control of magnetization and polarization with electric- and magnetic-fields in GdFeO$_{3}$, and attributed the controllability to novel, composite domain wall structure. \\[4pt] [1] Y. Tokunaga et al., Phys. Rev. Lett. \textbf{101}, 097205 (2008). \\[0pt] [2] Y. Tokunaga et al., Nature Mater. \textbf{8}, 558 (2009). [Preview Abstract] |
Wednesday, March 17, 2010 11:51AM - 12:03PM |
Q36.00002: Reduced metamagnetic transition fields in (Bi,Sm)FeO$_{3}$ single crystals Yoon Seok Oh, B.-G. Jeon, Seunghyun Khim, Jae Wook Kim, Kee Hoon Kim, Eun Sang Choi, D. Kan, I. Takeuchi For realizing useful magnetoelectric devices at room temperature, BiFeO$_{3}$ possesses several merits such as coexistence of ferroelectric and antiferromagnetic orders and large ferroelectric polarization. To increase the magnetoelectric coupling, it'll be also desirable to have a linear magnetoelectric effect, as originally anticipated in a hypothetical G-type antiferromagnetic ordering (3m) that can be realized in a $R3\bar{c}$ space group. Although the stabilization of a spiral spin ordering below 630 K, in reality, does not allow the linear magnetoelectric effect, it is known that the spiral spin structure can be broken under high magnetic fields to result in the linear magnetoelectric effect as well as weak ferromagnetism above 18 T. In this presentation, we report successful growth of high quality (Bi,Sm)FeO$_{3}$ single crystals by the flux method, and provide an electric/magnetic phase diagram up to high magnetic fields of 33 T. We find that the critical field for the weak ferromagnetic transition is reduced down to 6 T at room temperature, and anomalous magnetodielectric and magnetoelectric phenomena exist near the critical magnetic fields. [Preview Abstract] |
Wednesday, March 17, 2010 12:03PM - 12:15PM |
Q36.00003: Magnetoelectric properties of compositionally graded laminates at zero bias field S.K. Mandal, G. Sreenivasulu, V.M. Petrov, V.V. Zibtsev , G. Srinivasan This investigation focuses on magnetoelectric (ME) properties of compositionally graded magnetostrictive and piezoelectric trilayers. We studied magnetically induced electric field in a sample of nickel zinc ferrite (NZFO) with the grading axis perpendicular to the sample plane and lead zirconate titanate (PZT). Trilayers with two PZT layers with opposite poling direction and the ferrite in the middle were used to eliminate the standard ME effect stipulated by longitudinal deformations so that one measures ME output due to flexural deformation caused by grading effect. The data obtained for the dc and ac magnetic fields parallel to the sample plane showed a strong ME coupling even for zero external bias field. Theoretical modeling showed that this unconventional ME response can be accounted for by flexural deformation which arises from magnetic interaction between external ac magnetic field and internal dc magnetic field in the magnetic layer due to grading. The modeling results agree well with the data. -- work supported by grants from DARPA and NSF. [Preview Abstract] |
Wednesday, March 17, 2010 12:15PM - 12:27PM |
Q36.00004: Magnetodielectric phenomena in charge-spin coupled system in electronic ferroelectricity Makoto Naka, Sumio Ishihara Electronic ferroelectricity is known as phenomena where electric polarization is attributed to the charge order without inversion symmetry. This is seen in some transition metal oxides, e.g. LuFe$_{2}$O$_{4}$, and charge transfer salts. Quasi 2-dimesional organic salt kappa-(ET)$_{2}$Cu$_{2}$(CN)$_{3 }$is one of the kappa-ET salts of which two ET molecules construct a dimer and are arranged on a triangular lattice. Recently, it is reported that the increase of dielectric constant is experimentally observed below 60K. This indicates the presence of ferro (or anti-ferro) electric transition. An origin of the electric polarization is thought to be generated by a localized hole in one side of ET molecules in dimers [1,2]. We present a theory of magneto-dielectric phenomena in electronic ferroelectricity, in particular for this kappa-ET salt [3].We treat the electric dipole as a pseudo spin and construct an effective model Hamiltonian with the inter-dimer transfer integrals and the Coulomb interactions on a triangular lattice. We analyze this model by utilizing mean-field approximation and classical Monte-Carlo method, and investigate magnetodielectric phenomena which originate from spin-charge coupling and geometrical frustration. [1] T. Sasaki et al. (unpublished). [2] C. Hotta. (unpublished). [3] M. Naka and S. Ishihara. [Preview Abstract] |
Wednesday, March 17, 2010 12:27PM - 12:39PM |
Q36.00005: Element Specific Magnetic Ordering in Nd$_{0.75}$Dy$_{0.25}$Fe$_{3}$(BO$_{3})_{4}$ C.S. Nelson, L.N. Bezmaternykh, I.A. Gudim Interest in RFe$_{3}$(BO$_{3})_{4}$ has been motivated by the magnetoelectric properties of R = Gd and Nd, in which field-induced polarization phases are induced at modest ($<$1 T) magnetic fields. Spontaneous polarization has more recently been observed in the substituted ferroborate with R = Nd$_{0.75}$Dy$_{0.25}$.[1] Using rare earth L edge resonant x-ray scattering and nonresonant x-ray scattering, we have investigated the element specific magnetic ordering in Nd$_{0.75}$Dy$_{0.25}$Fe$_{3}$(BO$_{3})_{4}$ in an effort to shed light on the origin of its multiferroic behavior. Unlike in the R = Gd and Nd materials, the magnetic structure of Nd$_{0.75}$Dy$_{0.25}$Fe$_{3}$(BO$_{3})_{4}$ is observed to be strictly commensurate below T$_{N}$. In addition, a spin reorienation from easy axis toward easy plane is observed in the Nd and Fe subsystems with increasing temperature, and there is a decoupling between the two rare earth subsystems. The effects on the magnetic ordering of a magnetic field applied along the a-axis will also be discussed. Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886. [1] Y.F. Popov et al., JETP Lett. 8, 345 (2009). [Preview Abstract] |
Wednesday, March 17, 2010 12:39PM - 12:51PM |
Q36.00006: Magnetic order, spontaneous polarization, and magnetoelectric effect in rare earth iron borates: Ho$_{1-x}$Nd$_x$Fe$_3$(BO$_3$)$_4$ B. Lorenz, R. P. Chaudhury, Y. Y. Sun, C. R. dela Cruz, L. N. Bezmaternykh, V. L. Temerov, C. W. Chu Comprehensive results are presented for the thermodynamic, magnetic, dielectric, and magnetoelectric properties of HoFe$_3$(BO$_3$)$_4$ and the solid solution Ho$_{1-x}$Nd$_x$Fe$_3$(BO$_3$)$_4$ (x = 0.5 and 0.75). All compounds undergo a Ne\'{e}l order at T$_N>$ 30 K and a spin reorientation at T$_{SR}<$ 10 K. HoFe$_3$(BO$_3$)$_4$ shows a spontaneous electrical polarization below T$_N$ which decreases below T$_{SR}$ and in external magnetic fields. Ho$_{1-x}$Nd$_x$Fe$_3$(BO$_3$)$_4$ exhibits both, a spontaneous polarization and a large positive magnetoelectric effect. The superposition of spontaneous polarization induced by the internal magnetic field and the magnetoelectric polarization in external fields results in a complex behavior of the electrical polarization as function of temperature and/or magnetic fields. The magnetic order of HoFe$_3$(BO$_3$)$_4$ is further explored by neutron scattering experiments in external magnetic fields. [Preview Abstract] |
Wednesday, March 17, 2010 12:51PM - 1:03PM |
Q36.00007: Dilution Studies of Multiferroic ReFeO$_{3}$ with Bi Arthur Ramirez BiFeO$_{3}$ possesses simultaneous ferroelectric (T$_{c}$ = 1100 K) and antiferromagnetic (T$_{N}$ = 640 K) order but weak coupling between the states. The Fe moments in DyFeO$_{3 }$order at T$_{N}$ = 645 K and the Dy spins order below 4K, accompanied by an induced ferroelectric state. We study the interplay between Dy multiferroism in DyFeO$_{3 }$and Bi ferroelectricity in BiFeO$_{3 }$by measuring the magnetization of single crystals of the solid solution series (Dy,Bi)FeO$_{3}$. We find, for a limited range of Bi concentrations, an anomalous increase in the Dy ferromagnetic Curie temperature and cancellation of ferromagnetism on the Dy and Fe sublattices. We also study the effects of Bi substitution in ReFeO$_{3}$ for Re = Sm, Gd, Er, and Tm. [Preview Abstract] |
Wednesday, March 17, 2010 1:03PM - 1:15PM |
Q36.00008: H-T Phase Diagram of Multiferroic Sr2FeSi2O7 Jooseop Lee, Tae-Hwan Jang, Yoon Hee Jeong, Sungdae Ji, Naoyuki Katayama, Kirrily Rule, Manh Duc Le, Sung Chang, Seung-Hun Lee, Sang-Wook Cheong Using elastic neutron scattering, we have explored a new multiferroic Sr$_{2}$FeSi$_{2}$O$_{7}$ in the phase space of an external magnetic field (H) and temperature (T). At zero field, Sr2FeSi2O7 orders below 6 K into a collinear magnetic structure with a characteristic wavevector of (1,0,0.5). By applying H along the b-axis upto 14 Tesla at low temperatures, we identified four different magnetic phases, consistent with its bulk property data. All the magnetic states have a characteristic commensurate wave vector of either (1,0,0.5) or (1,0,0), indicating the magnetic structures remain collinear at the field-induced phase transitions. We have also determined the spin hamiltonian using inelastic neutron scattering with H = 0. [Preview Abstract] |
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