Electronic structure of Fe and magnetism in the 3d/5d3d/5d double perovskites Ca2_2FeReO6_6 and Ba2_2FeReO6_6

The Fe electronic structure and magnetism in (i) monoclinic Ca$_2$FeReO$_6$ with a metal-insulator transition at $T_{MI} \sim 140$ K and (ii) quasi-cubic half-metallic Ba$_2$FeReO$_6$ ceramic double perovskites are probed by soft x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD). These materials show distinct Fe $L_{2,3}$ XAS and XMCD spectra, which are primarily associated with their different average Fe oxidation states (close to Fe$^{3+}$ for Ca$_2$FeReO$_6$ and intermediate between Fe$^{2+}$ and Fe$^{3+}$ for Ba$_2$FeReO$_6$) despite being related by an isoelectronic (Ca$^{2+}$/Ba$^{2+}$) substitution. For Ca$_2$FeReO$_6$, the powder-averaged Fe spin moment along the field direction ($B = 5$ T), as probed by the XMCD experiment, is strongly reduced in comparison with the spontaneous Fe moment previously obtained by neutron diffraction, consistent with a scenario where the magnetic moments are constrained to remain within an easy plane. For $B=1$ T, the unsaturated XMCD signal is reduced below $T_{MI}$ consistent with a magnetic transition to an easy-axis state that further reduces the powder-averaged magnetization in the field direction. For Ba$_2$FeReO$_6$, the field-aligned Fe spins are larger than for Ca$_2$FeReO$_6$ ($B=5$ T) and the temperature dependence of the Fe magnetic moment is consistent with the magnetic ordering transition at $T_C^{Ba} = 305$ K. Our results illustrate the dramatic influence of the specific spin-orbital configuration of Re $5d$ electrons on the Fe $3d$ local magnetism of these Fe/Re double perovskites.Comment: 7 pages, 3 figure

Estimate of control voltage tolerances for a photo-electron analyzer of toroidal design

Sem informaçãoWe have run electron optics simulations and determined the tolerance in the control voltages of all elements (retarding input lens, analyzer, accelerating exit lens) of the La Trobe University photoelectron analyzer, recently redesigned to reach a spectral resolution of 5000, and which will be installed at LNLS (Campinas Brasil) and BESSY II (Berlin, Germany).We have run electron optics simulations and determined the tolerance in the control voltages of all elements (retarding input lens, analyzer, accelerating exit lens) of the La Trobe University photoelectron analyzer, recently redesigned to reach a spectral resolution of 5000, and which will be installed at LNLS (Campinas Brasil) and BESSY II (Berlin, Germany).We have run electron optics simulations and determined the tolerance in the control voltages of all elements (retarding input lens, analyzer, accelerating exit lens) of the La Trobe University photoelectron analyzer, recently redesigned to reach a spectral resolution of 5000, and which will be installed at LNLS (Campinas Brasil) and BESSY II (Berlin, Germany).334788791Sem informaçãoSem informaçãoSem informaçã

Investigation Of The Local Fe Magnetic Moments At The Grain Boundaries Of The Ca2 Fere O6 Double Perovskite

The local Fe ferromagnetic (FM) moment at the grain boundaries of a ceramic sample of Ca2 FeRe O6 double perovskite was investigated by means of x-ray magnetic circular dichroism spectroscopy at the Fe L2,3 edges and compared to the overall bulk magnetization. We found that, at the grain boundaries, the Fe FM moments at H=5 T are much smaller than expected and that the M×H curve is harder than in the bulk magnetization. These results suggest a larger degree of FeRe antisite disorder at the grain boundaries of this sample, shedding light into the intriguing nonmetallic resistivity behavior despite the reported presence of free carriers. © 2007 American Institute of Physics.1019Serrate, D., De Teresa, J.M., Ibarra, M.R., (2007) J. Phys.: Condens. Matter, 19, p. 023201Kobayashi, K.-I., Kimura, T., Sawada, H., Terakura, K., Tokura, Y., (1998) Nature (London), 395, p. 677Kobayashi, K.-I., Kimura, T., Tomoika, Y., Sawada, H., Terakura, K., Tokura, Y., (1999) Phys. Rev. B, 59, p. 11. , 159Prellier, W., Smolyaninova, V., Biswas, A., Galley, C., Greene, R.L., Ramesha, K., Gopalakrishnan, J., (2000) J. Phys.: Condens. Matter, 12, p. 965Gopalakrishnan, J., Chattopadhyay, A., Ogale, S.B., Venkatesan, T., Greene, R.L., Millis, A.J., Ramesha, K., Marest, G., (2000) Phys. Rev. B, 62, p. 9538Maignan, A., Raveau, B., Martin, C., Hervieu, M., (1999) J. Solid State Chem., 144, p. 224Dai, J.M., (2001) Mater. Sci. Eng., B, 83, p. 217Sarma, D.D., Mahadevan, P., Saha-Dasgupta, T., Ray, S., Kumar, A., (2000) Phys. Rev. Lett., 85, p. 2549Fang, Z., Terakura, K., Kanamori, J., (2001) Phys. Rev. B, 63, p. 180407Wu, H., (2001) Phys. Rev. B, 64, p. 125126Szotek, Z., Temmerman, W.M., Svane, A., Petit, L., Winter, H., (2003) Phys. Rev. B, 68, p. 104411Chattopadhyay, A., Millis, A.J., (2001) Phys. Rev. B, 64, p. 024424Aligia, A.A., Petrone, P., Sofo, J.O., Alascio, B., (2001) Phys. Rev. B, 64, p. 092414Kato, H., Okuda, T., Okimoto, Y., Tomoika, Y., Oikawa, K., Kamiyama, T., Tokural, Y., (2002) Phys. Rev. B, 65, p. 144404Westerburg, W., Lang, O., Ritter, C., Felser, C., Tremel, W., Jakob, G., (2002) Solid State Commun., 122, p. 201Oikawa, K., Kamiyama, T., Kato, H., Tokura, Y., (2003) J. Phys. Soc. Jpn., 72, p. 1411Granado, E., Huang, Q., Lynn, J.W., Gopalakrishnan, J., Greene, R.L., Ramesha, K., (2002) Phys. Rev. B, 66, p. 064409Iwasawa, H., Saitoh, T., Yamashita, Y., Ishii, D., Kato, H., Hamada, N., Tokura, Y., Sarma, D.D., (2005) Phys. Rev. B, 71, p. 075106Longo, J., Ward, R., (1961) J. Am. Chem. Soc., 83, p. 2816Alamelu, T., Varadaraju, U.V., Venkatesan, M., Douvalis, A.P., Coey, J.M.D., (2002) J. Appl. Phys., 91, p. 8909Serrate, D., De Teresa, J.M., Algarabel, P.A., Marquina, C., Morellon, L., Blasco, J., Ibarra, M.R., (2005) J. Magn. Magn. Mater., 290-291, p. 843De Teresa, J.M., Serrate, D., Blasco, J., Ibarra, M.R., Morellon, L., (2004) Phys. Rev. B, 69, p. 144401De Teresa, J.M., Serrate, D., Blasco, J., Ibarra, M.R., Morellon, L., (2005) J. Magn. Magn. Mater., 290-291, p. 1043Sikora, M., (2006) Appl. Phys. Lett., 89, p. 062509Azimonte, C., Cezar, J.C., Granado, E., Huang, Q., Lynn, J.W., Campoy, J.C.P., Gopalakrishnan, J., Ramesha, K., (2007) Phys. Rev. Lett., 98, p. 017204Abbate, M., (1992) Phys. Rev. B, 46, p. 4511Regan, T.J., Ohldag, H., Stamm, C., Nolting, F., Lning, J., Sthr, J., White, R.L., (2001) Phys. Rev. B, 64, p. 214422Thole, B.T., Carra, P., Sette, F., Van Der Laan, G., (1992) Phys. Rev. Lett., 68, p. 1943Carra, P., Thole, B.T., Altarelli, M., Wang, X.D., (1993) Phys. Rev. Lett., 70, p. 694Stohr, J., König, H., (1995) Phys. Rev. Lett., 75, p. 3748Teramura, Y., Tanaka, A., Jo, T., (1996) J. Phys. Soc. Jpn., 65, p. 105

Experimental exploration of the origin of magnetostriction in single crystalline iron

The magnetostrictive atomic strain in a pure Fe single crystal was measured by differential x-ray absorption spectroscopy. The obtained tetragonal magnetostriction constant, (3/2)λ100, was determined to be 45 ppm, consistent with the previously reported theoretical value calculated from a spin-orbit coupling theory. These results provide a foundation for understanding the origin of magnetostriction in pure Fe as well as Fe-based binary alloys

Polar atomic displacements in multiferroics observed via anomalous x-ray diffraction

The minute polar atomic displacements in multiferroics are shown to be within the reach of crystallography. A nonconventional methodology with anomalous x-ray diffraction is employed to investigate such displacements in DyMn(2)O(5) with giant magnetoelectric coupling and two distinct Mn(3+) and Mn(4+) sites. Intensity differences of a selected Bragg reflection were measured as the direction of electric polarization is switched by a poling field. A significant differential effect, which is strongly enhanced at energies near and above the Mn K edge, was observed near and below the ferroelectric transition temperature, T(c) similar to 40 K. The direct participation of ionic displacements in the ferroelectric polarization, particularly the Mn(3+) sublattice, is demonstrated, dismissing a purely electronic mechanism for the multiferroicity.81

Investigation of the local Fe magnetic moments at the grain boundaries of the Ca<SUB>2</SUB>FeReO<SUB>6</SUB> double perovskite

The local Fe ferromagnetic (FM) moment at the grain boundaries of a ceramic sample of Ca2FeReO6 double perovskite was investigated by means of x-ray magnetic circular dichroism spectroscopy at the Fe L2,3 edges and compared to the overall bulk magnetization. We found that, at the grain boundaries, the Fe FM moments at H = 5 T are much smaller than expected and that the MxH curve is harder than in the bulk magnetization. These results suggest a larger degree of Fe/Re antisite disorder at the grain boundaries of this sample, shedding light into the intriguing nonmetallic resistivity behavior despite the reported presence of free carriers

Experimental exploration of the origin of magnetostriction in single crystalline iron

The magnetostrictive atomic strain in a pure Fe single crystal was measured by differential x-ray absorption spectroscopy. The obtained tetragonal magnetostriction constant, (3/2)λ100, was determined to be 45 ppm, consistent with the previously reported theoretical value calculated from a spin-orbit coupling theory. These results provide a foundation for understanding the origin of magnetostriction in pure Fe as well as Fe-based binary alloys.The following article appeared in Applied Physics Letters 97 (2010): 072508 and may be found at http://dx.doi.org/10.1063/1.3481083.</p

Incipient orbital order in half-metallic Ba<SUB>2</SUB>FeReO<SUB>6</SUB>

Largely unquenched Re 5d orbital magnetic moments in half-metallic Ba2FeReO6 drive a symmetry lowering transition from a cubic paramagnet to a compressed tetragonal (c/a&lt;1) ferrimagnet below TC-305K, with a giant linear magnetoelastic constant and the spins lying spontaneously along the unique tetragonal axis. The large orbital magnetization and degree of structural deformation indicate proximity to a metal-insulator transition. These results point to an incipient orbitally ordered state in the metallic ferrimagnetic phase