Magnetic tunnel junction (MTJ) can serve as an excellent testbed for connecting Molecule between two ferromagnetic electrodes. A paramagnetic molecule covalently bonded to two ferromagnetic electrodes with two thiol functional groups can produce intriguing transport and magnetic properties. We have chemically bonded paramagnetic molecules between two ferromagnetic electrodes of a MTJ along the exposed side edges. In this paper we discussed the observation of Molecule induced dramatic changes in the magnetic and transport properties of the conventional magnetic tunnel junctions. Paramagnetic molecules were chemically bonded to ferromagnetic electrodes to bridge them across the insulating spacer along the exposed edges. Paramagnetic molecular channels along the tunnel junction edges decreased the overall current, through tunnel barrier and molecular channels, > 5 orders of magnitude below the leakage current of the bare tunnel junction at room temperature. These molecules caused significant changes in the spin density of states due to potential spin filtering effect. Also, paramagnetic molecules produced antiferromagnetic coupling between the affected magnetic electrodes. In this state spin transport in the magnetic tunnel junction based molecular devices plummeted by several orders. It is also noteworthy that our experimental studies provide a platform to connect a vast variety of ferromagnetic leads to the even broader array of high potential molecules such as single molecular magnets, porphyrin, and single ion molecules. The strength of exchange coupling between ferromagnetic electrodes and molecules can be tailored by utilizing different tethers and terminal functional groups. The MTJMSD can provide an advanced form of logic and memory devices, including a testbed for the Molecule based quantum computation devices. Future study about the interaction between molecular magnets and ferromagnets and interaction of thiol ended alkanes with ferromagnets will be of very valuable. This study indicates the potential of magnetic molecules as a mean to transforming conventional magnetic tunnel junctions and producing unprecedented magnetic and transport properties.
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Heterospin biradicals provide insight into molecular conductance and rectification
The correlation of electron transfer with molecular conductance ( g : electron transport through single molecules) by Nitzan and others has contributed to a fundamental understanding of single-molecule electronic materials. When an unsymmetric, dipolar molecule spans two electrodes, the possibility exists for different conductance values at equal, but opposite electrode biases. In the device configuration, these molecules serve as rectifiers of the current and the efficiency of the device is given by the rectification ratio (RR = g forward / g reverse ). Experimental determination of the RR is challenging since the orientation of the rectifying molecule with respect to the electrodes and with respect to the electrode bias direction is difficult to establish. Thus, while two different values of g can be measured and a RR calculated, one cannot easily assign each conductance value as being aligned with or opposed to the molecular dipole, and calculations are often required to resolve the uncertainty. Herein, we describe the properties of two isomeric, triplet ground state biradical molecules that serve as constant-bias analogs of single-molecule electronic devices. Through established theoretical relationships between g and electronic coupling, H 2 , and between H 2 and magnetic exchange coupling, J ( g ∝ H 2 ∝ J ), we use the ratio of experimental J -values for our two isomers to calculate a RR for an unsymmetric bridge molecule with known geometry relative to the two radical fragments of the molecule and at a spectroscopically-defined potential bias. Our experimental results are compared with device transport calculations.
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- Award ID(s):
- 1301346
- PAR ID:
- 10081782
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 8
- Issue:
- 8
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 5408 to 5415
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Understanding the magnetic molecules’ interaction with different combinations of metal electrodes is vital to advancing the molecular spintronics field. This paper describes experimental and theoretical understanding showing how paramagnetic single-molecule magnet (SMM) catalyzes long-range effects on metal electrodes and, in that process, loses its basic magnetic properties. For the first time, our Monte Carlo simulations, verified for consistency with regards to experimental studies, discuss the properties of the whole device and a generic paramagnetic molecule analog (GPMA) connected to the combinations of ferromagnet-ferromagnet, ferromagnet-paramagnet, and ferromagnet-antiferromagnet metal electrodes. We studied the magnetic moment vs. magnetic field of GPMA exchange coupled between two metal electrodes along the exposed side edge of cross junction-shaped magnetic tunnel junction (MTJ). We also studied GPMA-metal electrode interfaces’ magnetic moment vs. magnetic field response. We have also found that the MTJ dimension impacted the molecule response. This study suggests that SMM spin at the MTJ exposed sides offers a unique and high-yield method of connecting molecules to virtually endless magnetic and nonmagnetic electrodes and observing unprecedented phenomena in the molecular spintronics field.
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Spatial Impact Range of Single-Molecule Magnet (SMM) on Magnetic Tunnel Junction-Based Molecular Spintronic Devices (MTJMSDs) Marzieh Savadkoohi, Bishnu R Dahal, Eva Mutunga, Andrew Grizzle, Christopher D’Angelo, and Pawan Tyagi Magnetic Tunnel Junction-Based Molecular Spintronic Devices (MTJMSDs) are potential candidates for inventing highly correlated materials and devices. However, a knowledge gap exists about the impact of variation in length and thickness of ferromagnetic(FM) electrodes on molecular spintronics devices. This paper reports our experimental observations providing the dramatic impact of variation in ferromagnetic electrode length and thickness on paramagnetic molecule-based MTJMSD. Room temperature transport studies were performed to investigate the effect of FM electrode thickness. On the other hand, magnetic force microscopy measurements were conducted to understand the effect of FM electrode length extending beyond the molecular junction area, i.e., the site where paramagnetic molecules bridged between two FM. In the strong molecular coupling regime, transport study suggested thickness variation caused ~1000 to million-fold differences in junction conductivity. MFM study revealed near-zero magnetic contrast for pillar-shaped MTJMSD without any extended FM electrode. However, MFM images showed a multitude of microscopic magnetic phases on cross junction shaped MTJMSD where FM electrodes extended beyond the junction area. To understand the intriguing experimental results, we conducted an in-depth theoretical study using Monte Carlo Simulation (MCS) approach. MCS study utilized a Heisenberg atomic model of cross junction shaped MTJMSD to gain insights about room temperature transport and MFM experimental observations of microscopic MTJMSD. To make this study applicable for a wide variety of MTJMSDs, we systematically studied the effect of variation in molecular coupling strength between magnetic molecules and ferromagnetic (FM) electrodes of various dimensions.more » « less
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Paramagnetic single-molecule magnets (SMMs) interacting with the ferromagnetic electrodes of a magnetic tunnel junction (MTJ) produce a new system. The properties and future scope of new systems differ dramatically from the properties of isolated molecules and ferromagnets. However, it is unknown how far deep in the ferromagnetic electrode the impact of the paramagnetic molecule and ferromagnet interactions can travel for various levels of molecular spin states. Our prior experimental studies showed two types of paramagnetic SMMs, the hexanuclear Mn 6 and octanuclear Fe–Ni molecular complexes, covalently bonded to ferromagnets produced unprecedented strong antiferromagnetic coupling between two ferromagnets at room temperature leading to a number of intriguing observations (P. Tyagi, et al. , Org. Electron. , 2019, 64 , 188–194. P. Tyagi, et al. , RSC Adv. , 2020, 10 , (22), 13006–13015). This paper reports a Monte Carlo Simulations (MCS) study focusing on the impact of the molecular spin state on a cross junction shaped MTJ based molecular spintronics device (MTJMSD). Our MCS study focused on the Heisenberg model of MTJMSD and investigated the impact of various molecular coupling strengths, thermal energy, and molecular spin states. To gauge the impact of the molecular spin state on the region of ferromagnetic electrodes, we examined the spatial distribution of molecule-ferromagnet correlated phases. Our MCS study shows that under a strong coupling regime, the molecular spin state should be ∼30% of the ferromagnetic electrode's atomic spins to create long-range correlated phases.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C7SC00073A
