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Room Temperature Doped Ferromagnetic Oxides: - A current Scenario Towards Magnetic p-n Junctions K.V.Rao Dept of Materials Science-Tmfy, Royal Institute of Technology, Stockholm, Sweden A goal of spintronics is to develop a semiconductor that can manipulate the magnetism of an electron. Adding the spin degree of freedom to electronics will provide significant versatility and functionality to future electronic products. Although many possible electronic components, like for example the magnetic switch (Ohno et al) have been demonstrated, practical usefulness of the doped GaMnAs is limited by their Curie temperatures which currently lie below 300K. From this point of view, recently, ZnO based materials have been of growing interest following the first report [Sharma, P et al., Nature Mater.2, 673 (2003) with over 330 citations it is now the most cited paper from Nature Materials at present) of room temperature ferromagnetism in Mn doped ZnO thin films. With a band gap in the ultraviolet at 3.4 eV, ZnO based materials open up a variety of potential applications, especially for spinoptoelectronics, some of which already exist but currently independent of the spin considerations. Mn 2 + ion has the largest magnetic moment, 5 μ B, but often the moments measured experimentally have been rather small although the Tc’s have been above room temperature. Because the properties of ZnO are extremely sensitive to processing conditions, and the additional fact that Mn has many allotropes of oxides that are magnetic, it was shown by Sharma et al that the key to obtain above room temperature ferromagnetism is the deposition and processing at temperatures below 400 o C in a controlled atmosphere. These results have now been extensively reproduced often with considerably larger magnetic moments per Mn atom. Gamelin and his coworkers found that although the ‘as obtained’ nanocrystals produced by the colloidal approach were paramagnetic at room temperature, the films obtained by spincoating on to fused silica with a 2 min aerobic anneal at 500 o C became ferromagnetic with Tc above RT. In a subsequent experiment (JACS 127, 5292 (2005); PRL 94, 147209 (2005) they also showed that on Nitrogen-capping the colloidal particles during the processing of the thin films, gave a strong evidence for ferromagnetism with Mn in 2+ state, while on O-capping it was paramagnetic at room temperature. This result supports the prediction expected from a theoretical approach that the ferromagnetic order is carrier induced, and is via the holes in the p-state of ZnO. However, there are many recent experiments which evidence that, although carrier mediated, ferromagnetic order above RT is also obtained on n-type doping [Narayan et al APL 88, 242503 (2006)]. Another strong evidence for ferromagnetism in Mn doped ZnO is the significant magnetic circular dischroism at the ZnO band edge observed at room temperature. Along with such a result on doping ZnO with other TM elements it implies that ferromagnetism is an intrinsic property of the bulk ZnO lattice.(Neal et al PRL 96, 197208 (2006). Neal et al also observed that the MCD data at the ZnO band edge shows room temperature hysteretic behaviour. Recently, room temperature ferromagnetism in Mn doped ZnO has also been reported in nanorods, and freestanding single crystal nanowires, [e.g. APL 88, 263101 (2006)]. All the above facts and many more recent studies only confirm that we have robust ferromagnetism in Mn doped ZnO at room temperature and can be exploited for spintronic applications because of its high intrinsic Mn moment. Another challenging support and promise for device application comes from a recent observation that on Al co-doping Mn doped ZnO, Xu, X.H. et al [New J. Phys 8, 135 (2006)] obtained in their samples the full moment of Mn and in addition co-doping of Al resulted in n-type ZnO matrix. This is a significant observation, because we can now think of designing ferromagnetic n-p junctions at room temperature! Needless to stay that such an electronic element would not be possible with doped GaMnAs materials. It is always of interest to look for new and less complex materials suitable for applications in spintronics. In this context I will also present some highlights of our extensive studies of Room Temperature Ferromagnetism in semiconductors like ZnO, GaP, GaN In2O3.. doped with non-magnetic elements like Cu, V, Ti, Cr to mention a few among many others. Theoretical calculations based on the density functional theory (DFT) suggest that the most stable compounds of Tm(V, Cr Fe, and Ti) doped In 2 O 3 are all ferromagnetic at room temperature and specially in the case of V doping it gives rise to a rather strong ferromagnetic coupling, and the moment at the V site for example can be as large 2μ B The magnetic interactions are believed to be mediated by the hybridization between d-states of V and p-bands of oxygen. In Stockholm we have fabricated Cu doped ZnO films into patterned MRAM type structures with the patterned elements of size ranging from microns to nanometer scale by using ink-jet printing 120
technology, and e-beam lithography. We find that the ferromagnetic property is retained in these elements at all length scales. Further experiments towards device development are in progress. * Research supported by the Swedish funding Agency VINNOVA, and NM Spintronics in Stockholm. 121
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XXIII ΠΑΝΕΛΛΗΝΙΟ ΣΥΝΕ
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Κοιτώντας τα πρακτ
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ΕΠΙΤΡΟΠΕΣ Οργανωτι
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ΠΡΟΓΡΑΜΜΑ ΣΥΝΕΔΡΙΟ
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21. Οργανικά τρανζίσ
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15:30 15:45 16:00 16:15 16:30 16:45
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41. Modeling and quantitative phase
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Ανοιχτή Συνεδρία «
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«NανοΥλικά και Νανο
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New materials and MOS device concep
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Reliability Characteristics of Rare
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Ο λόγος των ταχυτήτ
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Thus the mean R In-In is expected t
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FIG 1. Schematic representation of
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με 0.80 eV στη διεπιφά
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Εντοπισµός Φορέων
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Παρασκευή και Xαρακ
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Electrical Spin Injection from Fe i
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Electrical Spin Injection of Spin-P
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References [1] CH Lee, J. Meteer, V
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Σχήμα 1: Φωτογραφία
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SEM Image Layout Simulation Εικ
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Μελέτη Ατελειών Σε
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Facet-Stress-Driven Ordering in SiG
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νανοκρυσταλλίτης (a
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Σχήµα 1. Εικόνες περ
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Σχήµα 1. Εικόνες περ
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Οι δομές που αναπτύ
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Raman Intensity (10 -50 cm 3 ) 1,2
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Μελέτη της Επίδρασ
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Annealing Induced Dissociation of N
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`Εναπόθεση με Παλμι
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Μελέτη της Χημείας
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Ανάπτυξη Νέων Μεσο
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Application of Thermal Quadrupoles
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Στοχαστική προσομο
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Νανοτραχύτητα κατά
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Ευαισθησία και Δια
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Optical Properties of CuIn 1-x Ga x
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ανοπτημένο με λέιζ
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Στο σχήμα 3 φαίνοντ
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Id (mA) -0,3 -0,2 -0,1 Vg=0 Vg=-1 V
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Strained-Si Si 1-x Ge x graded Si 1
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Fig. 1. Laser mask movement during
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(α) (β) Σχήμα 2: (α) Απε
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Figure 3. Generation 4 PAMAM-H 2 O
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Από όλα τα παραπάνω
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Το PHEGMA είναι άμορφο
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PS HAuCl 4 P2VP Ion loading PSP2VP
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The nonlinear optical response of A
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νανοσωµατίδια. Όπω
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Bioactive Glass/Nanodiamonds system
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Energy Loss Rates of Hot Electrons
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Σύνθεση και Χαρακτ
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μπορεί να ερμηνευτ
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Nανοσυνθέτα Εποξει
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[1] S. Iijima, Nature 354, 56 (1991
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Figure 3: GCMC calculations for und
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μερών, εμφανίζοντα
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1.0 Reflectance 1.1 1.0 0.9 0.8 0.7
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στο συντελεστή διέ
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¿ÔÖØÑÒØÓÐØÖÐÒÒÖÒ¸
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Συναπόθεση Cr - Ni σε
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Investigation of the Structural, Mo
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Modification of Perlite Cementitiou
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Templated Sol-Gel Synthesis Of TiO
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Παρασκευή Υμενίων
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Preparation of YSZ Solid Electrolyt
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Σύνθεση, Ανισοτροπ
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Μελέτη ανθρώπινων
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Local Coordination of Zn and Fe in
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Επίδραση της Προσθ
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Αλκαλική Σύνθεση κ
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Μηχανικές Iδιότητε
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The Influence of Thermal Aging on t
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Modeling and quantitative phase ana
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Συμβολή στη Συντήρ
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Κρυσταλλική Συµπερ
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Σύνθεση Στερεών ∆ι
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Fabrication and Characterization of
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∆ιερεύνηση δυνατό
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Συγκριτική αξιολόγ
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6 η Προφορική Συνεδ
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Ηλεκτρομαγνητική Α
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Φασματοσκοπική Μελ
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Thermal and Electrical Properties o
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Structure, Mechanical, and Optoelec
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Designing Nanoporous Materials for
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This program was developed to serve
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Νέα Αυτό-οργανούμε
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A Physical Model to Interpret the E
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FIR study of Ag x (As 33 S 33 Se 33
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Mελέτη Μεικτών Γυαλ
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The Structural Role of Fe and Zn in
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ΕΥΡΕΤΗΡΙΟ ΣΥΓΓΡΑΦΕ
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Κομπίτσας Μ…………
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ΕΥΡΕΤΗΡΙΟ ΣΥΓΓΡΑΦΕ
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W Watson I.M………………4 Weg
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xxiii ÏÎ±Î½ÎµÎ»Î»Î·Î½Î¹Î¿ ÏÏÎ½ÎµÎ´ÏÎ¹Î¿ ÏÏÏÎ¹ÎºÎ·Ï ÏÏÎµÏÎµÎ±Ï ÎºÎ±ÏÎ±ÏÏÎ±ÏÎ·Ï & ÎµÏÎ¹ÏÏÎ·Î¼Î·Ï ...