CORDIS - EU research results

Magnetic order induced in nonmagnetic solids

Final Report Summary - MAGNONMAG (Magnetic order induced in nonmagnetic solids)

1. A summary description of the project objectives

The objectives of this project are to establish a long-lasting collaboration and create a network of the research centres of excellence from Europe and Third Countries aiming at development of the novel scientific direction: magnetic order induced in nonmagnetic solids; to develop novel methods of control and manipulation of the magnetic degree of freedom in nominally nonmagnetic materials, in view of their potential for nanotechnology and nanoscience. The principal objective of theMagNonMag project is to establish an interdisciplinary training ground for both early stage researchers and experienced researches, enhancing the information partnership between theoretical and experimental research groups working in physics, chemistry, material science, and nanotechnology. The project is focused on nanomagnetism –magnetism shown by some materials on a nanoscale even if magnetically inert in the bulk – a novel physical effect with a potential for the emerging spintronics technology. TheMagNonMag project studies the possibility to control magnetism by various means such as introducing impurities and defects in nonmagnetic materials through ion bombardment, fluorination, and transmutation doping. The objects under investigation are IV group elements with the emphasis on graphite/graphene systems. Induced magnetism phenomena studied in this project have a potential to provide new effects and functionalities which are highly desirable and of great technological and economic relevance.

2. A description of the work performed since the beginning of the project

The joint investigations were performed via transfer of knowledge and networking activities between the four teams from Member States and three teams from the countries with an S&T agreement. This project is reinforcing and strengthening the existing bilateral scientific links and transforming them into a larger network which includes all partners. It is providing momentum for long-term collaboration between the partners, and the project findings and deliverables are lay the foundation for other actions in the PEOPLE Programme, aimed at further development and consolidation of the European Research Area and large scale competitive research projects that will be submitted in response to the HORIZONT 2020 in other themes. It is a multi- and inter-disciplinary project, which generated new knowledge by studying phenomena and manipulating spin degree of freedom at the nanoscale level.

3. A description of the main results achieved so far

We have succeeded in following methods of manipulating magnetism in otherwise nonmagnetic materials:

Decoration of graphene basal plane with nonmagnetic moities
Modulation of magnetism in graphene by a gate voltage
Theory of resonant indirect exchange
Magnetic ordering of dopant spins in Ge and Si
Magnetism in the vicinity of metal-insulator transition
Magnetism in graphite induced by ion irradiation
Magnetism of graphene decorated with aromatic radicals
Laser controlled magnetism in hydrogenated fullerene H:C60 film.
Light-induced superconductivity in K3C60

We have investigated several methods of inducing magnetism: traditional doping of semiconductors and their transmutation doping, irradiation, hydrogenation and fluorination. We followed the transition from antiferromagnetic to ferromagnetic ordering in the vicinity of metal-insulator transition. For the first time we show that low-dimensional magnetism is experimentally realized in agraphene-based system. Low-dimensional spin systems are in the focus of the present-day research due to a range of unusual properties governed by quantum effects. For example, spin liquid ground state, the superconducting and the excitonic insulator phases were predicted for zigzag graphene nanoribbons. Our results provide the first practical step towards fabrication of high-performance spin-valves and spin-filters from fluorinated graphene. We demonstrate that spontaneously formed disordered embedded graphene nanosegments create the pi-electron system with an antiferromagnetic ground state. The electrons remain forming a spin singlet unless a field corresponding to the bulk spin gap is applied. This idea was employed in first-principle calculations, where a spin-valve device was constructed on semiflourinated graphene as an antiferromagnetic semiconductor in a ground state. It was shown that hole doping due to the application of gate bias reduces the spin and charge excitation gap, making the ground state conducting and magnetic opening the possibility to create a spin filter.
4. The expected final results and their potential impact and use (including the socio-economic impact and the wider societal implications of the project so far)

Ongoing experimental efforts aimed at employing structural defects to turn graphene into an efficientspintronics material have been hindered by extremely low density of magnetic sites induced in a sheet with point defects or difficulties to produce perfect zigzag edges when graphene layer is cut into ribbons. The theory predicts exciting magnetic properties of graphene nanoribons, which have never been experimentally confirmed since intrinsic structural instability of the zigzag edges quenches magnetism. We have demonstrated that graphene fluorination rather than the breaking of the carbon-carbon bonds can be used as an efficient approach to generate strongly correlated magnetic states in this wonder material. Our results have the following potential impact:

(a). Industrial impact with possible societal implications. The exchange integral is higher than room temperature, J = 450 K which allows the on/offswitching between the nonmagnetic and magnetic states as a basic for graphene-based spintronic devices. Spin valve and spin filter will be made from available samples, as the practical step to carbon spintronics.

(b). Material science impact. Fluorine adsorption on graphene by a presented novel technology of monoatomic chains is a better way to produce graphene nanoribbons than cutting graphene since sliced nanoribbons with perfect zigzag edges are difficult to produce and preserve. Exploring the idea of the functionalization instead of the cutting of graphene layer as a route towards production of stable zigzag edges with localized magnetic states is a noticeable contribution to material science and graphene technology.

(c). Nanoelectronic impact. Chemically prepared, ultranarrow, ultrasmooth embedded graphenenanoribbons will find applications beyond magnetism, e.g. in electronics and optoelectronics, as tunable band gap materials.

(d). Scientific impact. (i) The first experimental evidence of the spin gap which is an essentially low-dimensional phenomenon and has a purely quantum origin will establish a new way of thinking about graphene magnetism. (ii) Demonstration of correlated ground state without symmetry breaking will cause a stir among the theoreticians looking for quantum spin liquid state in the honeycomb lattice. Graphene will enter the club of strongly correlated materials and will be a playground for such phenomena as spin liquid, spin glass, and spin ice states; unconventional magnetic orders; spin Peierls state, etc. (iii) Presentation of a graphene-based material with a spin-ladder structure may lead to the discovery of high-temperature superconductivity, as it already happened with the cuprates.

Our results are of interest to a broad community of scientists from material science and condensed matter physics with research interests as diverse as nanotechnologies, experimental solid state physics or many-body electron theory. The fascinating properties of graphene combined with possible applications in spintronics are also expected to attract the interest of the general public, policy-makers and businessmen.

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