Large resistance change on magnetic tunnel junction based molecular spintronics devices

Abstract

Molecular bridges covalently bonded to two ferromagnetic electrodes can transform ferromagnetic materials and produce intriguing spin transport characteristics. This paper discusses the impact of molecule induced strong coupling on the spin transport. To study molecular coupling effect organometallic molecular complex (OMC) was bridged between two ferromagnetic electrodes of a magnetic tunnel junction (Ta/Co/NiFe/AlOx/NiFe/Ta) along the exposed side edges. OMCs induced strong iter-ferromagnetic electrode coupling to yield drastic changes in transport properties of the magnetic tunnel junction testbed at the room temperature. These OMCs also transformed the magnetic properties of magnetic tunnel junctions. SQUID and ferromagnetic resonance studies provided insightful data to explain transport studies on the magnetic tunnel junction based molecular spintronics devices. Introduction:Connecting magnetic molecules between two ferromagnetic electrodes opens flood gate of opportunities for observing new phenomenon and making novel devices [1,2]. Initial studies focused on sandwiching molecules between two ferromagnetic leads [3]. In a more popular approach molecules were placed in a break-junction on a nanowire on a planar insulating substrate [4]. However, these two approaches have been extremely difficult to mass produce robust molecular spintronics devices [5]. With conventional approaches it is also almost impossible to conduct extensive magnetic studies to explore the true effect of molecules on the magnetic properties of the molecular spintronics devices [6]. To date most of the experimental studies have only focused on the transport studies-no direct magnetic measurements were performed [3,4,7]. To overcome the limitations of the conventional molecular spintronics devices magnetic tunnel junctions (MTJ), produced by sandwiching an insulator between two ferromagnetic electrodes, were utilized as the test bed [5,6,8]. Under this approach an MTJ with the exposed side edges can enables the covalent bonding of desired molecular channels onto the two ferromagnetic electrodes along the junction perimeter [5]. These molecules can be single molecular magnets [9], porphyrin [10], single ion molecules, and DNA [11]. This approach is equally capable of utilizing alkane like simple molecules with low spin orbit coupling and Zeeman splitting. The MTJ based molecular spintronics device (MTJMSD) approach enabled us to study the impact of paramagnetic molecules on the spin transport and magnetic properties of MTJs. This paper discusses experimental studies conducted before and after transforming an MTJ into MTJMSD. We report the observation of paramagnetic molecule induced dramatic changes in spin transport of an MTJ. We also report complementary SQUID and magnetic resonance studies exploring the underlying mechanism behind the impact of covalently bonded molecular channels between two ferromagnets of an MTJ testbed. Experimental details:To produce MTJ for MTJMSD, a bilayer ferromagnetic electrode was deposited by sequentially de...

Spin state of a single-molecule magnet (SMM) creating long-range ordering on ferromagnetic layers of a magnetic tunnel junction – a Monte Carlo study

“…The effect of molecular spin state strongly coupled to the FM electrodes was observed in several published studies by our group, 14,16,20,27,28 and others. 17 Unfortunately, it is extremely challenging to measure the exact molecular spin state connected between two ferromagnetic electrodes along the vertical multilayer edge of a tunnel junction (Fig.…”

“…32 We have also experimentally observed several orders of transient resistance change as a function of magnetic eld on OMC-based MTJMSD. 27 In other studies, where non-magnetic molecules were bridged between non-magnetic electrodes, above mentioned or resembling phenomenon was not observed. [33][34][35][36][37] Other groups have also observed strong coupling between C 60 molecules and ferromagnetism of the nickel electrodes leading to the Kondo splitting phenomenon without applying the estimated high magnetic eld needed for this observation.…”

“…The variation in S m and its impact on MTJMSD are expected to appear in the form of experimentally observed several orders of magnitude conductivity changes. 16,27 We also investigated the effect of S m and thermal energy on various parts of the MTJMSDs (Fig. 8).…”

GaAs(100) Surface Passivation with Sulfide and Fluoride Ions

“…Also, if GaAs is doped to acquire magnetic nature than the same molecule can also serve the additional role of establishing strong exchange coupling between the GaAs and ferromagnetic electrode leading to highly correlated materials, that can be termed as moleculebased metamaterials with unique physical properties [26][27][28]. In our prior study [26][27][28], paramagnetic molecules established unprecedented strong exchange coupling between two ferromagnetic electrodes. This exchange coupling resulted in intriguing current suppression and spin-dependent photovoltaic effect.…”

Molecular coupling competing with defects within insulator of the magnetic tunnel junction-based molecular spintronics devices

“…We have provided several intriguing observations resulting from molecule-induced strong antiferromagnetic coupling elsewhere 18 , 19 , 31 , 41 . The most striking observation is the room temperature current suppression phenomenon with cross junction shaped MTJMSD (Fig.…”