CERNINTC2006 005 and INTCP203 20 02 2006 Mssbauer

CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 Mössbauer studies of dilute magnetic semiconductors Marco Fanciulli MDM – CNR-INFM National Laboratory http: //www. mdm. infm. it M. Fanciulli - MDM – CNR-INFM National Laboratory

CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 The collaboration (1) Aarhus – (2) Berlin – (3) CERN – (4) Durban – (5) Milano – (6) Reykjavik M. Fanciulli 5, K. Bharuth-Ram 4, A. Debernardi 5, H. P. Gislason 6, H. P. Gunnlaugsson 1, Ö. Helgason 6, K. Johnston 3, R. Mantovan 5, S. Olafsson 6, D. Naidoo 4, R. Sielemann 2, G. Scarel 5, G. Weyer 1 Spokesperson: M. Fanciulli Contact person: K. Johnston M. Fanciulli - MDM – CNR-INFM National Laboratory

Main Objective CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 Understand the origin of the magnetic ordering in semiconducting and insulating oxides and control their magnetic properties M. Fanciulli - MDM – CNR-INFM National Laboratory

Main Motivations CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 Fundamental solid state physics: understand the mechanisms leading to magnetism in oxides and wide band gap semiconductors Applied solid state physics: spintronic devices (MTJ, spin valves, spin transistor), novel nanoelectronic devices (logic and memory), magneto-optic components, and QIP M. Fanciulli - MDM – CNR-INFM National Laboratory

Magnetism in Zn. O Doping with few percentages of 3 d metal impurities gives rise to room temperature magnetism. CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 The magnetism can be several Bohr magnetons pr. Impurity atom. Ivill et al. , JAP 97 (2003) 053904 JMD Coey M. Fanciulli - MDM – CNR-INFM National Laboratory

CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 -No magnetism under n-type growth conditions (O 2) while ptype conditions (N 2 O) are magnetic -Decrease in magnetic moment pr. Cu atom upon amount of Cu, attributed to close Cu pairs -TC > ~390 K observed M. Fanciulli - MDM – CNR-INFM National Laboratory

Role of defects CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 - Points out that the magentism is likely related to defects -Oxygen pressure during growth has major impact on the magnetic properties; attributed to oxygen vacancies. M. Fanciulli - MDM – CNR-INFM National Laboratory

CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 -Samples (2% Mn) grown by solid state reaction method -Sintering at ~900 K optimizes the magnetic properties (700 K - 800 K according to Coey) -Sintering in Ar produces more magnetism than samples sintered in O 2. M. Fanciulli - MDM – CNR-INFM National Laboratory

Magnetic ordering in Hf. O 2: conflicting results CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 • Growing interest in developing magnetic oxides and semiconductors for spintronics • Requirement: Curie temperature well above RT Undoped Hf. O 2 Experimental techniques that are able to study magnetism at the atomic scale are needed in order to clarify the nature of the observed macroscopic magnetism M. Fanciulli - MDM – CNR-INFM National Laboratory

Mössbauer Spectroscopy CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 M. Fanciulli - MDM – CNR-INFM National Laboratory

Mössbauer Spectroscopy CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 Isomer shift (position of spectral features): d ~ r(0) High spin Fe 3+ : 0. 35(10) mm/s High spin Fe 2+ : 1. 1(10) mm/s Quadrupole interaction (splitting of lines): DEQ ~ Vzz High spin Fe 3+ : 0. 5 -1 mm/s High spin Fe 2+ : 2 -3 mm/s Cubic crystals : 0. 0 mm/s Magnetic interactions (six line splitting of lines): Bhf ~ µ of site High spin Fe 3+ : µ = 5 µB, Bhf ~ 50 T High spin Fe 2+ : µ = 4 µB, Bhf ~ 40 T M. Fanciulli - MDM – CNR-INFM National Laboratory

Why 57 Mn implantation CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 • Truly dilute semiconductors are easily produced as only ~3· 1011 implanted probe atoms are needed to obtain a good spectrum (local concentration ~1017 cm-3). • Impurity concentrations and depth profiles are controllable. • Lattice defects are produced simultaneously and their interaction with the implanted probe atoms, possibly decisive for the occurrence of FM, can be studied, e. g. by varying the implantation temperature. • The half-life and decay properties of 57 Mn are favourable for such studies. • 57 Fe Mössbauer spectroscopy has sufficient sensitivity and resolution to obtain atomic scale information over a large temperature range of ~ 10 – 1000 K for studies of high TC magnetism. M. Fanciulli - MDM – CNR-INFM National Laboratory

Mössbauer Spectroscopy at ISOLDE CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 M. Fanciulli - MDM – CNR-INFM National Laboratory

Fe Lattice location in Zn. O CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 Implanted: 59 Mn Measured: (T½ = 4. 6 s) → 200 e. V recoil 59 Fe (T½ = 44 d) b- detected with position sensitive detector > 80% of the Fe atoms are located on substitutional Zn sites at T > 300 K M. Fanciulli - MDM – CNR-INFM National Laboratory

57 Mn implantation in Zn. O: test results CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 • Sextet: 47 T - 57 Fe-V complexes? • Magnetic field distribution: 31 T (average) - 57 Fe. I produced by the 40 e. V recoil energy • Quadrupole: 57 Fe on perturbed Zn sites • Single line at T>600 K - Origin? Dissolution of 57 Fe-V complexes? Velocity (mm/s) M. Fanciulli - MDM – CNR-INFM National Laboratory

Our proposal CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 • • • Low temperature measurements to see in more detail the effects of interstitial defects, which become mobile in the temperature range 77 – 300 K [22] as well as a possible mobility of Zn vacancies VZn. This should allow for better determination of the nature of the defects involved. (~ 4 shifts) Measurements in external magnetic fields to determine easy magnetisation axes and the sign of the magnetic hyperfine fields. In our current setup, we can reach external magnetic fields ~0. 7 T utilizing permanent magnets. (~3 shifts) Angular dependent measurements to determine Vzz axes and/or the angle between Vzz and Bhf. (~3 shifts) Measurements on differently doped Zn. O, pre-implanted/incorporated with 3 d impurities and n- and p-type doping. (~4 shifts) Measurements on other oxides and/or related systems (Hf. O 2, , Lu 2 O 3, Sn. O 2, Ti. O 2, Ga. N, Al. N and In. N). (~3 shifts) Time-delayed measurements: These are performed at a constant, critical temperature and spectra are measured in different time intervals after the implantation to give the annealing behaviour on a minute timescale. (~3 shifts) M. Fanciulli - MDM – CNR-INFM National Laboratory

Our requests CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 • Beam time: in lumps of 6 -10 shifts, during 2 -3 years 20 shifts in total. • The UC 2 target and the laser ion source are requested. M. Fanciulli - MDM – CNR-INFM National Laboratory

Complementary activities CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 • In parallel to the experiments planned at ISOLDE, a similar program involving stable 57 Fe atoms will be pursued in the home laboratories, however, much larger concentrations are needed for measurable effects. • For 2006 57 Fe recoil implantation experiments are also planned at HMI in Berlin. These experiments are complementary (57 Fe implantation and measurements during 100 ns) to those planned at ISOLDE. • Within the planned activity, we also foresee a collaboration with the PAC and PL groups at ISOLDE. M. Fanciulli - MDM – CNR-INFM National Laboratory

Relevant resources at home institutions CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 • CNR-INFM MDM National Laboratory (M. Fanciulli, R. Mantovan): - Conversion electron Mössbauer spectroscopy (MS) at RT and at 120 K - ESR and EDMR (X and Q band, 300 m. K – 600 K, up to 12 T) - Growth by Atomic Layer Deposition (ALD) of oxides (G. Scarel) - First principle calculations of magnetic properties of Fe doped Zn. O (A. Debernardi) • University of Aarhus: Conversion electron Mössbauer spectroscopy (MS) at RT and transmission MS at 14 -300 K on samples with stable isotopes. (H. P. Gunnlaugsson) Theoretical calculation of Mössbauer parameters of model defects (A. Svane) • University of Iceland: MBE growth of Ga. N, Al. N and In. N samples, with or without Mn doping, C-V and Hall effect and PL characterisation, (S. Olafsson and Prof. H. P. Gislason). Transmission MS from 300 -1000 K, (Prof Ö. Helgason). • University of Kwa. Zulu-Natal, Durban, and i. Themba LABS, South Africa ( K. Bharuth-Ram): Transmission MS at 80 – 1000 K; CEMS at RT Vibrating sample magnetometer M. Fanciulli - MDM – CNR-INFM National Laboratory

Conclusions CERN-INTC-2006 -005 and INTC-P-203 20. 02. 2006 • Mössbauer spectroscopy following implantation of radioactive 57 Mn into oxide systems is a powerful method to investigate the magnetism in these systems. • The experimental procedures can be expanded providing additional relevant information (other systems, orientation, external magnetic field, extended T range, rotation). • Complementary experimental techniques will be also involved at ISOLDE and at home Labs. • Theoretical work directly connected with the experiments will be also carried out by the collaboration. M. Fanciulli - MDM – CNR-INFM National Laboratory