II Materials � Chalcospinels � Delafossite oxides � Dilute oxide nanoparticles � Al-doped Co:ZnO thin films � Future work MANSE Midterm Review
Staff, Publications • M Venkatesan Senior postdoc • Karsten Rode Postdoc • Delphine Lebeugle Postdoc • Jonathan Alaria Postgrad • Marita O’Sullivan Postgrad • Simone Alborgetti Postgrad MANSE Midterm Review
Publications: —Oxide dilute magnetic semicondutors – Fact or Fiction? J.M.D. Coey, S.A. Chambers, MRS Bulletin 33 1063-8 (2009) —Dilute magnetic oxides and nitrides, K. Rode and J. M. D. Coey, in Handbook of Magnetism and Advanced Magnetic Materials (H Kronmullar and S Parkin, editors), Vol 4, pp 2107 – 2121 (2007) —Dilute magnetic oxides, J. M. D. Coey, Comments on Solid State and Materials Sciences 10 83-92 (2007) —Magnetism in dilute magnetic oxide thin fi lms based on SnO 2 , C. B. Fitzgerald, M. Venkatesan, L. S. Dorneles, R. Gunning, P. Stamenov, J. M. D. Coey, P. A. Stampe, R. J. Kennedy, E. C. Moreira and U. S. Sias, Physical Review B, 74, 115307 (2006) — Giant moment and magnetic anisotropy in Co-doped ZnO fi lms grown by pulse- injection metal organic chemical vapor deposition, A. Zukova, A. Teiserskis, S. van Dijken, Y. K. Gun’ko and V. Kazlauskiene, Applied Physics Letters, 89, 232503 (2006) — Charge-transfer ferromagnetism in oxide nanoparticles, JMD Coey, Kwanruthai Wongsaprom, J. Alaria and M. Venkatesan, Journal of Physics D: Applied Physics, 41, 134012 (2008) — Magnetic, magnetotransport and optical properties of Al-doped Co-doped ZnO thin films M. Venkatesan, P. Stamenov, L. S. Dorneles, R. D. Gunning and J. M. D. Coey, Applied Physics Letters 90 242508 (2007) —Magnetic and structural properties of Co-doped ZnO thin films, L.S. Dorneles, M. Venkatesan, R. Gunning, P. Stamenov. J. Alaria, M. Rooney, J.G. Lunney, J.M.D. Coey, Journal of Magnetism and Magnetic Materials 310 2087-2088 (2007) MANSE Midterm Review
— Room temperature ferromagnetism in Mn- and Fe-doped indium tin oxide thin films, M. Venkatesan, R.D. Gunning, P. Stamenov, J.M.D. Coey, Journal of Applied Physics, 103, 07D135 (2008) — Structural and magnetic properties of wurzite CoO thin films, J. Alaria, N. Cheval, K. Rode, M. Venkatesan and J.M.D. Coey, Journal of Physics D: Applied Physics, 41, 135004 (2008) — Magnetism of ZnO nanoparticles doped with 3d cations prepared by a solvothermal Method, J. Alaria, M.Venkatesan and J.M.D. Coey, Journal of Applied Physics 103 07D123 (2008) —Magnetism’s ticklish giant, Nature Materials 5 677-8 (2006) —Magnetic properties of CN x whiskers. R. D. Gunning, M. Venkatesan, D. H. Grayson and J. M. D. Coey, Carbon, 44 3213-7 (2006) —The origin of Magnetism of etched silicon. P. Grace, M. Venkatesan, J. Alaria and J.M.D. Coey, Advanced Materials (in press) —Absence of toroidal moments in aromagnetic anthracene. S. Alborghetti, E. Puppin, M. Brenna, E. Pinotti, P. Zanni, J.M.D. Coey, New Journal of Physics 10 063019 (2008) —Thin films of semiconducting lithium ferrite produced by pulsed laser deposition, R.D. Gunning, Karsten Rode, Sumesh R.G. Sophin, M. Venkatesan, JMD Coey, Igor V. Shvets, Applied Surface Science (in press) —Half-metallic Ferromagnets, M. Venkatesan, in Handbook of Magnetism and Advanced Magnetic Materials (H Kronmullar and S Parkin, editors), Vol 4, pp 2133 – 2156 (2007) MANSE Midterm Review
— Ferromagnetic nanoparticles with strong surface anisotropy: Spin structures and magnetisation processes, L. Berger, Y. Labaye, M. Tamine, J.M.D. Coey, Physical Review B 77 104431 (2008) — Magnetic anisotropy of ilmenite-hematite solid solution thin films grown by pulsed laser ablation, K. Rode, R.D. Gunning, R.G.S. Sofin, M. Venkatesan, J.G. Lunney, J.M.D. Coey and I.V. Shvets, Journal of Magnetism and Magnetic Materials, 320, 3238 (2008) —Permanent Magnets, T. Ni Mhiochain and J. M. D. Coey, Encyclopedia of Life Support Systems Volume 3: Physical methods, instruments and measurements, Y. M. Tsipenyuk (editor),.Chapter 10 pp 203 – 258 EOLSS/UNESCO Paris (2007) MANSE Midterm Review
Characterization • X-ray/Neutron diffraction • SEM/EDAX/RBS/AFM/MFM/HRTEM • SQUID magnetometry • Optical spectrometry • XAS/XES/XMCD • Transport measurements MANSE Midterm Review
I. Chalcospinels Chalcospinels Normal cubic spinel structure. n-type magnetic semiconductors CuCr 2 S 4 T C = 420 K 4.6 µ B /f.u CuCr 2 Se 4 T C = 460 K 4.9 µ B /f.u CdCr 2 Se 4 T C = 130 K Conduction electrons may be fully spin polarized - potential half-metal? A red shift (0.05 eV) of the absorption edge on passing the T C . High room temperature magneto-optical Kerr effect (1.2º at 0.9 eV). MANSE Midterm Review
CuCr 2 Se 4 ceramic Prepared at 550° C (below peritectic transition) MANSE Midterm Review
High temperature synthesis Temp ( ° C) σ ( µ B ) @5K 550 6.0 750 5.5 850 5.2 MANSE Midterm Review
PLD films Deposition conditions Growth of CuCr 2 Se 4 thin films from ceramic target Ceramic target Substrate c-Al 2 O 3 , MgO, MgAl 2 O 4 , RT-700°C 1 J/cm 2 5Hz Pressure ~ 10 -6 mbar Metallic target Substrate MgO 200°C 1 J/cm 2 5Hz Pressure ~10 -6 mbar Annealing process 500° C in Se Vapour (from elemental Se powder) in a vacuum sealed quartz tube for 48 hours MANSE Midterm Review
Magnetizaton Before Annealing After Annealing Films from metallic target Polycrystalline samples, mixed phases MANSE Midterm Review
CuCr 2 Se 4-x Br x Powders Powders • Synthesis temperature is critical. • Saturation magnetic moment of 6 µ B /mol can be achieved in CuCr 2 Se 4 made at 550 C. It is probably a half-metal. Single crystals Single crystals • Metallic (CuCr 2 Se 4 ) or intrinsic semiconductor (CdCr 2 Se 4 ) when undoped • Anomalous Hall effect and AMR Thin films Thin films • ~ Single phase after annealing MANSE Midterm Review
Next steps � Complete torque curves � Complete torque curves � Low � Low- -temperature heat capacity temperature heat capacity � IR optical conductivity (with � IR optical conductivity (with Dimitri Dimitri Basov, UCSD) Basov, UCSD) � Thermal conductivity � Thermal conductivity � Neutron diffraction (LLB April) � Neutron diffraction (LLB April) � Andreev reflection � Andreev reflection � AC Squid � -15 15 A m 2 for AC Squid magnetometry magnetometry; Sensitivity 3 10 ; Sensitivity 3 10 - A m 2 for dc fields < 1 T. dc fields < 1 T. If the mobility permits, demonstrate an all-ferromagnetic transistor. MANSE Midterm Review
II. Delafossite oxides Cu-delafossite is still considered to be a potential p-type semiconductor for transparent electronics. CuAlO 2 CuCrO 2 :Ca,Mg CuInO 2 :Mg,Sn Carrier density and mobility are the major factors that require to be improved. MANSE Midterm Review
CuCrO 2 CuCrO 2 p-type t ransparent c onducting o xide (TCO) Delafossite structure: A 1+ B 3+ O 2 Crystal system: Rhombohedral Space group: R-3m Lattice parameters: a = 2.9761(2) Å, c = 17.102(1) Å Bandgap: 3.2 eV Antiferromagnetic: T N = 25K Mg-doped CuCrO 2 High conductivity for p-type TCO: 220 S/cm (5% Mg) Thermopower +153 � V/K at 300K 50% transparent to visible light (250 nm thick film) MANSE Midterm Review
PLD films 800 (006) H2103CCMO (0012) (009) 10% Mg 2 O (111) (0018) (003) (101) Cu 750 (202) CuO, CuCr2O4 H2201CCO H2301CCO H2401CCO CuCrO2 Cu2O (006) 5% Mg H1703C CMO 700 (0012) (003) Intensity (arb. units) (009) (0018) 2 (101) O (202) r C u C 650 H2501CCO H2701CCO H2801CCO (006) o C) H0502CCM O CuCr2O4 (0012) CuCrO2 Cu 2 O (111) (009) Cu2O (003) (0018) T ( 2% Mg 2 O (220) (101) 600 (202) Cu (006) H2301CCO (0012) 550 (003) H2901CCO2 H2801CCO2 H2901CCO (009) Amorphous Amorphous (0018) (101) (202) Cu2O Undoped 500 10 20 30 40 50 60 70 80 90 100 110 120 2 θ (deg) 450 0.1 1 10 100 1000 ����������������� P O 2 ( µ µ bar) µ µ Mg Doping P ( μ bar) T ( o C) Fluence Rep Rate Thickness Conductivity (2 (J/cm 2 ) (Hz) (nm) probe) H2301CCO Undoped 10 700 1.9 5 63 ∞ H0502CCMO 2% 10 650 1.0 2 20 5 M Ω H1703CCMO 5% 20 650 1.5 1 31 600 k Ω H2103CCMO 10% 20 650 1.5 2 40 10 k Ω MANSE Midterm Review
10% Mg-CuCrO 2 /0.1% Al-ZnO/(0001)/Al 2 O 3 10% Mg 0.06 6.0 100000 H2611ZCO_6 * 5.5 0.05 5.0 (006) CuCrO2 (002) ZnO -1 ) 10000 ln( σ ) (Scm 4.5 (101) CuCrO2 0.04 4.0 Intensity (C) 1000 (009) CuCrO2 3.5 0.03 ρ ( Ω cm) 3.0 100 2.5 0.02 0 10 20 30 40 50 60 70 -1 ) 1000/T (K 10 0.01 1 0.00 H2103CCMO 20 25 30 35 40 45 50 0 50 100 150 200 250 300 2 θ (deg) T (K) MANSE Midterm Review
Summary Growth of highly-crystalline native p-type delafossite oxide films CuCrO 2 , CuAlO 2 Good quality n-type Al:ZnO films are also grown by PLD (mobility ~ 20 cm 2 V -1 s) Next steps: Make all-oxide heterostructures; pn junctions and pnp stacks. Use sapphire shadow masks. MANSE Midterm Review
III. Dilute oxide nanoparticles LSTO nanoparticle system Tokura et al, PRL 1988 � spd -band metal. � 0.5 electrons per formula � γ = 5 mJ mol -1 K -2 � properties depend on oxygen stoichiometry Systematic investigation of the magnetic properties of LSTO, undoped and with transition metal doping (substitution for Ti at the 1.5 or 2.0 % level) for dopants ranging from Sc to Ni. MANSE Midterm Review
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