Electrically Programmable Magnetoresistance in Multifunctional Organic‐Based Spin Valve Devices

Abstract

Information and communication technology (ICT) is now calling for solutions enabling lower power consumption, further miniaturization, and multifunctionality requiring the development of new device concepts and new materials. [ 1 ] One of the most fertile approaches to meet such demands is spintronics, which is now facing the challenge of evolving from the fi rst generation of devices that led to a revolution in information storage [ 2 ] (giant magnetoresistance readheads), to devices that exhibit multioperation capabilities (logic, communication, and storage) within the same materials technology. [ 3 ] Indeed, the electrical control of the magnetoresistance (MR) can provide such capabilities and is currently being pursued along several lines. In inorganic spintronics the two main approaches are the use of combined ferromagnetic or ferroelectric materials [ 4 ] and spin-polarized-current-induced control of the electrode magnetization. [ 5 ] In this paper we show that an electrically controlled magnetoresistance can be easily achieved in organic devices by combining magnetic bistability (spin valve) and electrical memory effects into an interacting multifunctional implementation.Electrical resistive switching effects in organic-based devices have recently received widespread attention [ 6 ] and represent one of the most promising ICT applications. On the other hand, spintronic devices based on organic semiconductors (OSC) have already provided signifi cant results [ 7 ] and device performances. [ 8 ] An essential device employed in the fi eld is the one commonly known as a spin valve, in which a spin-polarized current is injected from a ferromagnetic electrode into the organic transport medium and collected subsequently by a second ferromagnetic electrode. The latter acts as a spin analyzer due to the different collection probabilities for electrons arriving with different spin orientations, [ 9 ] giving rise to a measurable spin valve magnetoresistance (SVMR). The organic transport medium can be either a single molecule or, as in this communication, a thin fi lm. The former case pertains to the fi eld of molecular spintronics, while the latter belongs to organic spintronics. SVMR in organic semiconductors has been shown in a number of devices featuring several OSC and different ferromagnetic electrodes, giving evidence of spin injection in the conducting levels of OSCs. Recently this was unambiguously confi rmed by muon spin rotation and two-photon photoemission spectroscopy. [ 10 , 11 ] Previously we documented the coexistence of magnetoresistive and non-volatile electrical switchings in tris (8-hydroxyquinolinato)aluminium (Alq 3 )-based vertical spin valves with manganite and cobalt electrodes. [ 12 ] Such a coexistence was recently reported for rubrene-based devices with similar electrodes. [ 13 ] In this paper we go beyond these results by demonstrating a full electrical control of the magnitude of the spin valve effect: the SVMR can be turned "on" and "off" as well as smoothly tuned between a number of no...

Impurity-band transport in organic spin valves

“…The impurities might be metal atoms, which serve as donors, or O 2 molecules, which serve as acceptors. The presence of highdensity impurities in the OSVs is further supported by the accompanying memory effect 22 caused by charge storage, as in the electroformed inorganic structures 20,21 . Such memory effects are not expected from the organic diode of Fig.…”

Room-temperature air-stable spin transport in bathocuproine-based spin valves

“…First, the temperature dependence of the resistance of most organic SVs is weak [7][8][9][10][11][12][13][14][15][16][17] , resembling more the behaviour of a tunnel junction than the temperature-activated transport typical of organic films 21 . Therefore, the question rises whether the SVs are actually probing the properties of the organics, or they are prone to artifacts coming from the interpenetration of the top metal contact into the organic layer.…”

“…In addition to the long spin lifetimes, it has been noticed that the combination of molecules and FM offers other intriguing possibilities for spintronics. For instance, devices with novel functionalities have been demonstrated by exploiting properties of the semiconducting molecules, such as light emission 16 , electrical bistability 17 and hot electron filtering 18 . Furthermore, reaction at a molecule/FM interface can result in interfacial states 19,20 with modified energetics and spin polarization.…”

Optically Detected Magnetic Resonance Studies on π-conjugated semiconductor systems

“…Thus, the mechanism behind the positive spin-1/2 ELDMR in rubrene-doped Alq 3 devices is the same as the mechanism behind the positive spin-1/2 PLDMR in MEH-PPV films, i.e., enhanced annihilation of TE-polaron pairs (TPQ) that reduces the TE and polaron populations under resonance conditions, and in turn reduces the quenching of SEs by TEs and polarons. Higher j produces more polarons on Alq 3 moledcules, which enhances the 42 TPQ effects, including ELDMR.…”

“…It is reported that a strong spin valve effect of ~22% was achieved in a tris(8-hydroxyquinolinato) aluminium (Alq 3 )-based device [42].…”