Juliana Marques Ramos 1,2 German Thesis Advisor: Reiner Vianden 2, Brazilian Thesis Advisor: Artur Wilson Carbonari 1 Collaborators: João Guilherme Martins Correia, Rafael Sá de Freitas and ISOLDE collaboration Carrier Mobility and Magnetic Interactions in TiO 2 1 Instituto de Pesquisãs Energéticas e Nucleares, São Paulo University, Brazil 2 Helmholtz-Instituts für Strahlen- und Kernphysik, Bonn University, Germany

Non volatility + Current control trough spin - Increase density of information stored per unit area and the speed of data processing; - Reduces energy consumption; [1] FERT, A. Review of Modern Physics, v. 80 n.4, 1517, [2] MOLNAR, V. S.; READ, D. New materials for semiconductor spin-electronics.Proceedings of the IEEE. v.91, p , [3] WOLF, S. A.;et. al.Spintronics: A Spin-Based Electronics Vision for the Future.Science,v. 294, p , Current control trough spin + Optic properties - The combination of the two materials in a single chip would function of various devices: - Gather logic, communication skills, collective storage and detection [1]. To magnetic semiconductors The control of spin-dependent phenomena in semiconductors can lead to devices such as spin light-emitting diodes (spin-LEDs), spin field effect transistors (spin-FETs) e spin qubits for quantic computers [2, 3]. Motivation From magnetic metals...

Fe doping Candidate as DMS [1] Defects produced by the doping Candidate as DMS [1,2] Related works [1] J. M. D. Coey, M. Venkatesan and C. B. Fitzgerald, Nature Materials, 4 (2005) 173. [2] S. K. S. Patel, S. Kurian, N. S. Gajbhiye, AIP Advances, 2 (2012) RTFM “The absence of any sextet in fit-derived Mössbauer spectra clearly showed that the ferromagnetic component in the samples is not due to metallic iron and iron oxide."

Results Presence of magnetization’s saturation as a function of the field; Presence of the hysteresis curve M (H); Low coercive field (applications which require switching) Significant remanent magnetization (non volatile behavior)

Results Rapid increase of the magnetization at a certain critical temperature; Subtle anomaly near 50 K; The magnetization of a paramagnet also increases when we decrease the temperature.

Considerations - Value of coercive field (low) and remanence. - Macroscopic measurements provide only indications of a possible existence of FM long-range order (not to be confused with FM correlations that occurs even at high temperature). - To be sure of ferromagnetic long-range ordering - Origin of FM: existence of clusters? carry out neutron diffraction and observe magnetic diffraction peaks. PAC Spectroscopy γ1γ1 γ2γ2 Coincidence Magnetic interaction: Quadrupole interaction:

PAC Results: TiO 2 + 3% Fe Probe nuclei diffused! Sample has still a lot of defects! V zz ~ 6 x V/m 2 Site 1: η ~ 0.2 Site 2: η ~ 0.8 Site 1: δ ~ 3 % Site 2: δ ~ 25 % Site 1: f ~ 40 % Site 2: f ~ 60 %

PAC Results: TiO 2 + 3% Fe

Site 1Site 2 V zz = 6 x V/m 2 V zz = 7 x V/m 2 η = 0.28 (0.01)η = 0.71 (0.01) δ = 4 % (0.05)δ = 20 % (0.08) f = 23 % (2)f = 77 % (7) ω L = 1,74 (0.13) Mrad/s B = 0,115 Tω L = 13,6 (1.1) Mrad/s B = 0,925 T 13 K 27 K Site 1Site 2 V zz = 6 x V/m 2 V zz = 7 x V/m 2 η = 0.27 (0.01)η = 0.7 (0.01) δ = 2 % (0.01)δ = 15 % (0.1) f = 22 % (2.1)f = 80 % (6) ω L = 1,74 (0.11) Mrad/s B = 0,115 Tω L = 13,76 (1.01) Mrad/s B = 0,945 T 70 K: (too weak)/no magnetic ordering

PAC Results: TiO 2

IS 481 PAC Results: TiO 2 111m Cd

PAC Results: TiO Hf

After the EC decay of the 111 In and the following Auger process, the 111 Cd atom is in a highly unstable charged state. In semiconductor oxides, depending on the electronic and structural properties of the impurity–host system, the 111 Cd probe can trap some electron holes for a time long enough (in the order of ns) to reach the sensitive intermediate state of the 111 Cd nuclei. In the time interval of the PAC coincidence detection, transitions between different charge states out of the equilibrium can occur producing a time-dependent EFG at the 111 Cd site.

Summary Room temperature ferromagnetism Two electric quadrupole interactions Weak magnetism: not applicable in spintronic! Time dependent EFG at 111 Cd site Future Work X-ray absorption fine structure (EXAFS) measurements Neutron diffraction: long-range ferromagnetic ordering? To be sure of ferromagnetic long-range ordering we will carry out neutron diffraction and observed magnetic diffraction peaks. Looking for a Post Doc position…

Reactor team! Dr. Reiner Vianden Me! Mr. Marius Arenz IS481: Poster Section Dr. Patrick Kessler Thank you! Obrigada! Danke sehr!