S. P. Mathew

Bio: S. P. Mathew is an academic researcher from Weizmann Institute of Science. The author has contributed to research in topics: Magnetization & Magnetoresistance. The author has an hindex of 12, co-authored 19 publications receiving 689 citations. Previous affiliations of S. P. Mathew include Hebrew University of Jerusalem & St. Joseph's College, Devagiri.

Helicenes—A New Class of Organic Spin Filter

Abstract: Chiral helicene, a fully conjugated system without stereogenic carbon, can filter spins effectively at room temperature, a consequence of the chiral-induced spin-selectivity effect. The chirality dictates the spin of the electrons transferred through helicene, and magnetoresistance devices based on these molecules show antisymmetric magnetoresistance versus H plots.

A chiral-based magnetic memory device without a permanent magnet

Abstract: Most new device concepts for random-access memory are based on inorganic spin filters, which need a permanent magnet to operate. Here, the authors exploit the chiral-induced spin selectivity effect in an organic spin filter to construct a novel type of memory device, which works without a permanent magnet.

Chiral Conductive Polymers as Spin Filters

Abstract: DOI: 10.1002/adma.201405249 electrode. By controlling the direction of the magnetization of nickel, it is possible to inject electrons that have mainly one spin orientation and to verify their transport through the PCT by monitoring the cyclic voltammetry (CV) curve in the electrochemical cell in which the redox couple is not chiral. The CV curves refl ect a steady state in which a double layer is formed near the working electrode. Another method to monitor the spin selectivity is by chronoamperometry, in which one monitors time-dependent current at a fi xed potential. At the beginning, when the potential is turned on, the current is high, but it is reduced with time due to the formation of the double layer. [ 18,19 ]

Cold denaturation induces inversion of dipole and spin transfer in chiral peptide monolayers.

Abstract: Chirality-induced spin selectivity is a recently-discovered effect, which results in spin selectivity for electrons transmitted through chiral peptide monolayers. Here, we use this spin selectivity to probe the organization of self-assembled α-helix peptide monolayers and examine the relation between structural and spin transfer phenomena. We show that the α-helix structure of oligopeptides based on alanine and aminoisobutyric acid is transformed to a more linear one upon cooling. This process is similar to the known cold denaturation in peptides, but here the self-assembled monolayer plays the role of the solvent. The structural change results in a flip in the direction of the electrical dipole moment of the adsorbed molecules. The dipole flip is accompanied by a concomitant change in the spin that is preferred in electron transfer through the molecules, observed via a new solid-state hybrid organic-inorganic device that is based on the Hall effect, but operates with no external magnetic field or magnetic material.

Non-magnetic organic/inorganic spin injector at room temperature

Abstract: Spin injection into solid-state devices is commonly performed by use of ferromagnetic metal electrodes. Here, we present a spin injector design without permanent magnet; rather, the spin selectivity is determined by a chiral tunneling barrier. The chiral tunneling barrier is composed of an ultrathin Al2O3 layer that is deposited on top of a chiral self-assembled monolayer (SAM), which consists of cysteine or oligopeptide molecules. The experimentally observed magnetoresistance can be up to 20% at room temperature, and it displays an uncommon asymmetric curve as a function of the applied magnetic field. These findings show that the spin injector transmits only one spin orientation, independent of external magnetic field. The sign of the magnetoresistance depends on the handedness of the molecules in the SAM, which act as a spin filter, and the magnitude of the magnetoresistance depends only weakly on temperature.

Materials Challenges for High Performance Magnetocaloric Refrigeration Devices

Abstract: Magnetocaloric materials with a Curie temperature near room temperature have attracted significant interest for some time due to their possible application for high-efficiency refrigeration devices. This review focuses on a number of key issues of relevance for the characterization, performance and implementation of such materials in actual devices. The phenomenology and fundamental thermodynamics of magnetocaloric materials is discussed, as well as the hysteresis behavior often found in first-order materials. A number of theoretical and experimental approaches and their implications are reviewed. The question of how to evaluate the suitability of a given material for use in a magnetocaloric device is covered in some detail, including a critical assessment of a number of common performance metrics. Of particular interest is which non-magnetocaloric properties need to be considered in this connection. An overview of several important materials classes is given before considering the performance of materials in actual devices. Finally, an outlook on further developments is presented.

Chiral molecules and the electron spin

Abstract: The electron’s spin is essential to the stability of matter, and control over the spin opens up avenues for manipulating the properties of molecules and materials. The Pauli exclusion principle requires that two electrons in a single spatial eigenstate have opposite spins, and this fact dictates basic features of atomic states and chemical bond formation. The energy associated with interacting electron clouds changes with their relative spin orientation, and by manipulating the spin directions, one can guide chemical transformations. However, controlling the relative spin orientation of electrons located on two reactants (atoms, molecules or surfaces) has proved challenging. Recent developments based on the chiral-induced spin selectivity (CISS) effect show that the spin orientation is linked to molecular symmetry and can be controlled in ways not previously imagined. For example, the combination of chiral molecules and electron spin opens up a new approach to (enantio)selective chemistry. This Review describes the theoretical concepts underlying the CISS effect and illustrates its importance by discussing some of its manifestations in chemistry, biology and physics. Specifically, we discuss how the CISS effect allows for efficient long-range electron transfer in chiral molecules and how it affects biorecognition processes. Several applications of the effect are presented, and the importance of controlling relative spin orientations in multi-electron processes, such as electrochemical water splitting, is emphasized. We describe the enantiospecific interaction between ferromagnetic substrates and chiral molecules and how it enables the separation of enantiomers with ferromagnets. Lastly, we discuss the relevance of CISS effects to biological electron transfer, enantioselectivity and CISS-based spintronics applications. Chiral molecules can filter electrons according to their spin. This chiral-induced spin selectivity (CISS) effect can have important applications, such as in spintronics and in enantioseparation. This Review describes the CISS effect, its mechanism and its fascinating applications.

The added value of small-molecule chirality in technological applications

Abstract: Chirality is a fundamental symmetry property; chiral objects, such as chiral small molecules, exist as a pair of non-superimposable mirror images. Although small-molecule chirality is routinely considered in biologically focused application areas (such as drug discovery and chemical biology), other areas of scientific development have not considered small-molecule chirality to be central to their approach. In this Review, we highlight recent research in which chirality has enabled advancement in technological applications. We showcase examples in which the presence of small-molecule chirality is exploited in ways beyond the simple interaction of two different chiral molecules; this can enable the detection and emission of chiral light, help to control molecular motion, or provide a means to control electron spin and bulk charge transport. Thus, we demonstrate that small-molecule chirality is a highly promising avenue for a wide range of technologically oriented scientific endeavours. Although it is a fundamental property of many small molecules, chirality is not widely exploited in materials applications as its benefits are not widely recognized — indeed, the need for stereoselective synthesis may be seen as a disadvantage. In this Review, we highlight recent research in which chirality has had an enabling impact in technological applications.

Spintronics and Chirality: Spin Selectivity in Electron Transport Through Chiral Molecules

Abstract: Recent experiments have demonstrated that the electron transmission yield through chiral molecules depends on the electron spin orientation. This phenomenon has been termed the chiral-induced spin selectivity (CISS) effect, and it provides a challenge to theory and promise for organic molecule– based spintronic devices. This article reviews recent developments in our understanding of CISS. Different theoretical models have been used to describe the effect; however, they all presume an unusually large spin-orbit coupling in chiral molecules for the effect to display the magnitudes seen in experiments. A simplified model for an electron’s transport through a chiral potential suggests that these large couplings can be manifested. Techniques for measuring spin-selective electron transport through molecules are overviewed, and some examples of recent experiments are described. Finally, we present results obtained by studying several systems, and we describe the possible application of the CISS effect for memory devices.