Voltage-controlled oxide barriers in organic/hybrid spin valves based on tunneling anisotropic magnetoresistance

Grünewald, M.; Homonnay, N.; Kleinlein, Johannes; Schmidt, G.

doi:10.1103/physrevb.90.205208

Cited by 17 publications

(23 citation statements)

References 50 publications

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“…The bars indicate the respective relative magnitude of the MR. Already here it is visible that the MR not only changes its amplitude but also its sign, much in contrast to results of Prezioso et al 3,4 and Grünewald et al 5 The corresponding full MR traces are plotted in Fig. 3.…”

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confidence: 63%

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Resistive switching and voltage induced modulation of tunneling magnetoresistance in nanosized perpendicular organic spin valves

et al. 2016

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Nanoscale multifunctional perpendicular organic spin valves have been fabricated. The devices based on an La 0.7 Sr 0.3 MnO 3 /Alq3/Co trilayer show resistive switching of up to 4-5 orders of magnitude and magnetoresistance as high as -70% the latter even changing sign when voltage pulses are applied. This combination of phenomena is typically observed in multiferroic tunnel junctions where it is attributed to magnetoelectric coupling between a ferromagnet and a ferroelectric material. Modeling indicates that here the switching originates from a modification of the La 0.7 Sr 0.3 MnO 3 surface. This modification influences the tunneling of charge carriers and thus both the electrical resistance and the tunneling magnetoresistance which occurs at pinholes in the organic layer.In the past years a number of multiferroic tunnel junctions have been demonstrated in which tunneling magnetoresistance (TMR) and total device resistance can be modulated by a voltage pulse. 1,2 The effects are typically explained by tunneling electroresistance (TER) due to a ferroelectric barrier which changes the total resistance and magnetoelectric coupling at the interface between ferroelectric barrier and ferromagnetic contact which changes the TMR in magnitude and sometimes in sign. We observe the same functionality in organic spin valves (OSVs, Fig. 1), which after applying a voltage pulse may change the device resistance by three orders of magnitude or more and modulate their magnetoresistance (MR) from +26% to -38% which is a much larger effect than observed in Refs. 1 or 2. Nevertheless, the absence of a ferroelectric layer in our devices excludes both TER and magnetoelectric coupling as possible explanation. It should, however, be noted that our devices and those from Refs. 1 and 2 have a La 0.7 Sr 0.3 MnO 3 (LSMO) bottom electrode as a common property.FIG. 1: MR traces of a nanosized OSV (LSMO/Alq3/MgO/Co/Ru with 20/12/3/30/10 nm in thickness) for two different resistance states after different voltage pulses taken at 4.3 K. The resistance changes by approx. three decades and the relative MR exhibit a sign reversal from +26% to -38%. Already in 2011 the simultaneous observation of magnetoresistance and resistive switching (RS) has been reported for organic spin valves by Prezioso et al. 3,4 In this case the devices were LSMO/Alq3/Co-based spin valves showing a relative MR of -20% in the initial state. By applying 2 voltage pulses the overall device resistance was increased while the relative MR decreased without changing shape or sign. The device resistance could be increased by two decades while the MR was completely suppressed. A possible explanation suggested by Prezioso et al. was the blocking of filaments or charge trapping in combination with giant magnetoresistance (GMR) and spin injection as a prevalent transport mechanism, however, no clear identification of the underlying physics was possible. Recent results from our own group in structures with only one ferromagnetic electrode (LSMO) also demonstrated RS. However, in thi...

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confidence: 63%

“…But secondly our devices also exhibit RS which modulates the MR. This effect is well investigated by Grünewald et al 5 and has successfully been modeled by a variable rectangular tunneling barrier created by oxygen vacancies at the Alq3/LSMO interface. These positive oxygen vacancies are formed at the LSMO/Alq3 interface.…”

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confidence: 87%

Resistive switching and voltage induced modulation of tunneling magnetoresistance in nanosized perpendicular organic spin valves

et al. 2016

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“…The tunnel barrier can be introduced at the metal/SC interface commonly by two ways: tailoring the band bending in SC, which typically leads to Schottky barrier formation or physically inserting a discrete insulating layer. Interestingly, the conductivity mismatch has been thought to be less severe when using OSCs since carriers are injected into the OSCs mainly by tunneling through an insulating barrier, naturally formed during the fabrication process (either by thermal evaporation or solution processing) . For example, several incredibly large MR responses in OSVs have been reported in literature where the tunnel barrier was not explicitly inserted .…”

Section: Fundamental Conceptsmentioning

confidence: 99%

Organic Spin Valves: A Review

Devkota

Geng

Subedi

et al. 2016

Adv Funct Materials

101

106

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accelerated impressively and advanced to a range of materials and a number of techniques to verify the successful injection and transport of the SP carriers. [ 1,2,10,11 ] The effect has been realized in a variety of materials combinations such as FM fi lms, FM/anti-FM coupled layers, or FM semiconductors as the injection/detection electrodes and the metals, superconductors, inorganic semiconductors, organic semiconductors, and insulators including ferroelectric and topological insulators as the spacers. [ 1,2,[12][13][14][15][16][17][18] The GMR effect was extensively studied using non-magnetic metallic interlayer and its applications such as electric switching, magnetic recording, and sensors were suggested and employed. [ 1,2,16 ] However, all-metallic spintronic devices imposed restrictions in applications as they are characterized by short spin relaxation time (≈picosecond) and are not suitable for coherent spin manipulation. [ 1,2,19 ] To overcome these limitations, the spintronics community caught its attention towards hybrid devices with semiconductors (SCs) sandwiched in between the FM layers and continued advancing to a range of semiconducting materials. [ 2,14,[20][21][22] The organic semiconductors (OSCs) are among the youngest members of the spacer materials and were fi rst tested in the spintronic devices only about a decade ago. Nevertheless, OSC devices have been of continuously advancing research topics over the past three decades for their rich physics, fl exible chemi stry, cost effi ciency, and potential applications in new generations of electronic devices including organic light emitting diodes (OLEDs), [23][24][25] organic solar cells, [ 26,27 ] and organic fi eld effect transistor. [ 28,29 ] In fact, OLEDs have already revolutionized the modern display industry and spin-dependent devices such as organic spin valves (OSVs), OLED-based magnetic sensors, and spin-OLEDs are under intensive study to achieve their new avenues. [30][31][32] This increasing interest on organic electronics is for their several distinctions over inorganic counterparts. [19][20][21]33,34 ] Electronically, the band theory explains the electric transport in inorganic SCs while charge hopping is the main transport mechanism in the OSCs with much smaller carrier mobility. This is a favorable condition for large electron-hole pair recombination without the need of using a p-n junction structure. [23][24][25] Spintronically, the inorganic SCs contain heavy atoms giving rise to a large spin-orbit coupling (SOC), which is a response of the electron spin degree of freedom to its orbital environment. The strength of the SOC in solids depends upon the nature of orbital wave functions of electrons and the materials structure. [ 35 ] In case of hydrogenic wave-function-like electrons (s-orbital electrons), it is Organic spintronics is an emerging and potential platform for future electronic devices. Signifi cant progress has been made in understanding the spin injection, manipulation, and detection in organic spin valves in the p...

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“…[22][23][24][25][26] TAMR [22][23][24][25][26] arises when there is tunnelling across a resistive tunnel barrier, on one side of which lies a ferromagnetic electrode that undergoes non-180 magnetic switching. This happens because spin-orbit coupling in the ferromagnet couples the magnetization direction to the tunnelling density of states, 22 such that TAMR adopts the symmetry of the electrode if the tunnel barrier is centrosymmetric.…”

Section: -Graphene Interfacesmentioning

confidence: 99%

“…The TAMR magnitude in our devices is similar to the low-temperature values obtained with LSMO electrodes. 25,26 However, TAMR in device 1 is reduced with respect to device 2, probably because structural relaxation reduces the degree of LSMO distortion (supplementary note 2). 34 More generally, the interpretation of bias-dependent TAMR is challenging, 24,52 as it is influenced by all of the electronic bulk/interfacial states in the electrodes.…”

Section: à2mentioning

confidence: 99%

Tunnelling anisotropic magnetoresistance at La0.67Sr0.33MnO3-graphene interfaces

Phillips

Lombardo

Ghidini

et al. 2016

Applied Physics Letters

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Using ferromagnetic La0.67Sr0.33MnO3 electrodes bridged by single-layer graphene, we observe magnetoresistive changes of ∼32–35 MΩ at 5 K. Magneto-optical Kerr effect microscopy at the same temperature reveals that the magnetoresistance arises from in-plane reorientations of electrode magnetization, evidencing tunnelling anisotropic magnetoresistance at the La0.67Sr0.33MnO3-graphene interfaces. Large resistance switching without spin transport through the non-magnetic channel could be attractive for graphene-based magnetic-sensing applications.

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Voltage-controlled oxide barriers in organic/hybrid spin valves based on tunneling anisotropic magnetoresistance

Cited by 17 publications

References 50 publications

Resistive switching and voltage induced modulation of tunneling magnetoresistance in nanosized perpendicular organic spin valves

Resistive switching and voltage induced modulation of tunneling magnetoresistance in nanosized perpendicular organic spin valves

Organic Spin Valves: A Review

Tunnelling anisotropic magnetoresistance at La0.67Sr0.33MnO3-graphene interfaces

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