Spinterface: A new platform for spintronics

Since its discovery in early 2000's Molecular Spintronics has developed in an established and fructuous research field, achieving a number of outstanding results and unveiling unusual spintronic properties. Typically the most mysterious device element, the interface, in molecular spintronics has on contrary received and enormous attention and even gained a special nickname – the spinterface. Based on significant efforts of many research groups worldwide it has been established its critical role in defining the main functionalities of molecular spintronic devices. Noteworthily the spinterface was found to control the properties of the both components constituting the interface, not only those of the molecular layer but surprisingly also those of the magnetic counterpart. This paper aims to overview the most striking spinterface properties and to highlight the possibilities to promote new device paradigms based on interfacial modulation. Keywords: Molecular spintronics, Ferromagnetism, Spin polarization, Hybridization organic semiconductor

Controlling magnetoresistance by oxygen impurities in Mq3-based molecular spin valves

The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semiconductors is still incomplete after its demonstration more than a decade ago. While carrier concentration may play an essential role in spin transport in these devices, direct experimental evidence of its importance is lacking. We probed the role of charge carrier concentration by studying the interplay between MR and multilevel resistive switching in OSVs. The present work demonstrates that all salient features of these devices, particularly the intimate correlation between MR and resistance, can be accounted for by the impurity band model, based on oxygen migration. Finally, we highlight the critical importance of carrier concentration in determining spin transport and MR in OSVs and the role of interface-mediated oxygen migration in controlling the OSVs response

Conditions for the growth of smooth La0.7Sr0.3MnO3 thin films by pulsed electron ablation

We report on the optimisation of the growth conditions of manganite La0.7Sr0.3MnO3 (LSMO) thin films prepared by Channel Spark Ablation (CSA). CSA belongs to pulsed electron deposition methods and its energetic and deposition parameters are quite similar to those of pulsed laser deposition. The method has been already proven to provide manganite films with good magnetic properties, but the films were generally relatively rough (a few nm coarseness). Here we show that increasing the oxygen deposition pressure with respect to previously used regimes, reduces the surface roughness down to unit cell size while maintaining a robust magnetism. We analyse in detail the effect of other deposition parameters, like accelerating voltage, discharging energy, and temperature and provide on this basis a set of optimal conditions for the growth of atomically flat films. The thicknesses for which atomically flat surface was achieved is as high as about 10-20 nm, corresponding to films with room temperature magnetism. We believe such magnetic layers represent appealing and suitable electrodes for various spintronic devices.Comment: original paper, thin film optimization, 25 pages, 9 figure

Magnetoresistance and energy model of Alq3-based spintronic devices

Spin transport in organic semiconductors has been receiving widespread attention since the first experimental demonstration of magnetoresistive effects (change in resistance under an applied magnetic field) in hybrid ferromagnetic/organic/ferromagnetic structures [1]. Continuous effort in the field has led to the realization, for example, of vertical organic spintronic devices with differ- ent organic semiconductor layers [2,3] or organic tunnel barriers [4]. However, there is still a lack of understanding on the mechanism that governs spin injection and transport in organics, leading to general disagreement even on the expected sign of the devices output magnetoresistance. With the aim to clarify the spin transport behaviour in organic semiconductors, we present new results on hybrid inorganic/organic spin valves with the most successful up-to-date combination of materials [2-6]. The highly spin polarized manganite La2/3Sr1/3MnO3 and Cobalt have been used as ferromagnetic electrodes for spin injection into thick layers (up to 200 nm) of tris(8-hydrox- yquinoline)aluminum(III) (Alq3). In a critical design improvement, we have for the first time intro- duced an artificial tunnel barrier (Al2O3 or LiF) between the organic and the Co top electrode to study its influence on spin injection into organic semiconductors and to improve the chemical sta- bility and reproducibility of the devices. In our manuscript we: explore the importance of artificial tunnel barriers for spin injection in organics, record room temperature magnetoresistance, demonstrate that only ferromagnetic elec- trodes and not organic semiconductor limit device output and, finally, sketch an energy diagram able to explain negative magnetoresistance in LSMO/Alq3/Co spin valves. Our work is a new step forward in organic spintronics, as we prove that organic semiconductors do not have a clear limit for room temperature performance with the adequate ferromagnets, and we present a reliable model that could be easily extrapolated to predict the output of different materi- als combinations in hybrid spin valves. [1] Dediu, V., Murgia, M., Matacotta, F.C., Taliani, C. & Barbanera, S. Sol. State Commun. 122, 181-184 (2002). [2] Xiong, Z.H., Wu, D., Vardeny, Z.V. & Shi, J. Nature 427, 821-824 (2004). [3] Majumdar, S., Majumdar, H.S., Laiho, R. & Osterbacka, R. J. Alloy & Compounds 423, 169-171 (2006). [4] Santos, T.S., Lee, J.S., Migdal, P., Lekshmi, I.C., Satpati, B. & Moodera, J.S. Phys. Rev. Lett. 98, 016601 (2007). [5] Xu, W., Szulczewski, G.J., LeClair, P., Navarrete, I., Schad, R., Miao, G., Guo, H. & Gupta, A. Appl. Phys. Lett. 90, 072506 (2007). [6] Hueso, L.E., Riminucci, A., Bergenti, I., Zhan, Y. & Dediu, V. Adv. Mater. 19, 2639-2642 (2007)

Oxygen impurities link bistability and magnetoresistance in organic spin valves

Vertical cross-bar devices based on manganite and cobalt injecting electrodes and metal-quinoline molecular transport layer are known to manifest both magnetoresistance and electrical bistability. The two effects are strongly interwoven, inspiring new device applications such as electrical control of the magnetoresistance and magnetic modulation of bistability. To investigate the full device functionality, we first identify the mechanism responsible for electrical switching by associating the electrical conductivity and the impedance behavior with chemical states of buried layers obtained by in operando photoelectron spectroscopy. These measurements revealed that a significant fraction of oxygen ions migrates under voltage polarity, resulting in a modification of the electronic properties of the organic material and of the oxidation of interfacial layer with ferromagnetic contacts. Variable oxygen doping of the organic molecule represents the key element for correlating bistability and magnetoresistance and our measurements provide the first experimental evidence in favor of the impurity band model describing the spin transport in organic semiconductors in similar devices

Multi-modal sensing in spin crossover compounds

We exploited the solvatochromic spin-state switching in a spin crossover (SCO) compound based on the Fe-II complex and the simultaneous change of spectroscopic properties for selective multimodal sensing of methanol and ethanol. We demonstrate that sensing capabilities are due to the inclusion of methanol or ethanol molecules into the crystalline structure, which tailors simultaneously the transition temperature, colour, birefringence and vibrational modes. We exploited this capability by integrating a neutral compound, switchable at room temperature, into a micrometric TAG sensitive to the colour and birefringence. The system was characterised by optical microscopy, magnetic susceptibility, Raman spectroscopy and X-ray diffraction

Spin injection in the doped bad metal SrTiO3

In this paper, we demonstrate the capability to establish spin-polarized currents in doped SrTiO3 (STO). The results are based on the study of charge and spin transport in STO layers doped by the reversible electromigration of oxygen atoms in resistive-switching La0.7Sr0.3MnO3/STO/Co vertical stacks. The formation of oxygen vacancies inside STO results in a metallic conductivity at temperatures <200–250 K, above which a transitionto an insulating like behavior is detected. A detailed theoretical analysis shows that the behavior of the metallic phase in our samples corresponds to the well-known state of the thermodynamically doped STO featuring the so-called bad metal behavior. Thus, our findings introduce this class of unconventional materials as valuable candidates for innovative spintronic devices