Ferromagnetic liquid crystals were predicted more than 40 years ago by Brochard in de Gennes. This work is the first experimental proof of their theory. Ferrimagnetic barium-hexaferrite nanoplates are the basis of the ferromagnetic liquid crystal. Their synthesis was developed within the research program P2-0089. The crucial property of the incorporated magnetic nanoparticles is their plate-like shape that originates from their crystal structure, in addition to their size and magnetic properties. The synthesis of the applicable nanoparticles was developed under hydrothermal conditions in a combination with partial chemical substitution of Fe3+ with Sc3+. The final incorporation of the nanoparticles into a liquid crystal was made possible by the specific control of their surface properties. Due to the coupling between the liquid-crystal director and the magnetic moments of the nanoplates the optical properties of ferromagnetic liquid crystals can be tuned with electric or magnetic field. The work represents the only publication in Nature authored with exclusively Slovenian authors. This break-through work has already triggered wide new research (10 new original scientific articles only in the frame the first reaseacrh team), both theoretical and experimental in different fields of science and also initiated development of new technologies.
COBISS.SI-ID: 27304231
A ferromagnetic suspension in an isotropic media is presented for the first time in this article in Nature Communications journal (IF=12.35). The basis for this development is magnetic nanoplates of Ba hexaferrite. The synthesis of the Ba hexaferrite nanoplates and the preparation of their suspensions were developed at in the frame of this Programme P2-0089. When the concentration of nanoplates’ suspensions the in butanol is high enough they spontaneously order in nematic liquid-crystal phase resulting in ferromagnetic ordering. The suspensions behave similar to ferromagnetic liquid-crystal suspensions, which were also developed with our participation. However, the unique property of the ferromagnetic suspensions in isotropic solvents is their extremely high sensitivity to a magnetic field. Namely, these suspensions are sensitive even to Earth's magnetic field, which makes them suitable for liquid magnetic-field sensors. The work actually represent of new type of polar materials –ferromagnetic ferrofluids, which can pave the way to development of new technologies. It has already triggered new research in complex-materials physics and in sensorics.
COBISS.SI-ID: 29253927
This review article in in a high-impact-factor journal Progress in Materials Science (IF=23.75) is a recognition of excellent scientific achievements of our colleague, D. Lisjak, in the field of magnetic materials based on barium hexaferrite. The article was written in co-authorship with A. Mertelj after an invitation from the Editorial board (Prof. Dr. T. Massalski, now retired). It reviews long-term research of anisotropic magnetnic nanoparticles that, in addition to their nano dimensions, show scientifically relevant and applicable properties due to their anisotropic shapes.
COBISS.SI-ID: 31275559
We thoroughly analysed how the crystalline structure and magnetic properties evolve in parallel with the particles morphology during the hydrothermal synthesis of barium-hexaferrite nanoplatelets. At the same time, we managed to show for the first time how the crystalline structure adapts when materials with a complex, layered structure are confined at the nanoscale. Such layered materials include many families of technologically important mixed oxides, e.g., ferroelectric Aurivillius phases, superconducting cuprates. When such materials are prepared in the form of small nanoparticles they adopt a specific structure and composition defined by a termination of the particle at its surfaces with a specific, low-energy atomic layer. After hydrothermal synthesis at low temperatures the barium-hexaferrite nanoplatelets exhibit the structure defined by a termination at the Ba-containing planes, and as the result, the Ba-rich composition. However, during subsequent washing the surface changes and the structure of nanoplatelets can be represented by a SRS* sequence of the barium-hexaferrite SRS*R* unit cell, where S and R represent a hexagonal (BaFe6O11)2- and a cubic (Fe6O8)2+ structural block, respectively. With growth, the structure changes in a stepwise manner, by the discrete addition of the SR segments to the initial SRS* structure. The addition of just one RS segment (SRS*R*S structure) gives the nanoplatelets hard magnetic properties. Understanding of the processes during hydrothermal synthesis will enable further improvement in the size control and in final magnetic properties.
COBISS.SI-ID: 31549735
Bi-magnetic, platelet nanoparticles combining a hard-magnetic Ba-hexaferrite (BaFe12O19) platelet core in between two soft-magnetic iron oxide maghemite (gamma-Fe2O3) layers were presented for the first time. The nanoparticles were synthesized using a new, simple and inexpensive method based on the co-precipitation of Fe3+/Fe2+ ions in a colloidal aqueous suspension of the hexaferrite core nanoparticles. The hexaferrite displays high magnetocrystalline anisotropy, however, modest saturation magnetization. By combining the hexaferrite core with the soft magnetic shell in single nano-unit, the saturation magnetization can be strongly increased. Moreover, the topotactic growth of the maghemite shell on the hexaferrite core supported the direct magnetic coupling between the core and the shell, resulting in a large increase of the remanence and, as a result, of the energy product (BH)max , a figure of merit for the quality of permanent magnets (for more than twice compared to the core alone).
COBISS.SI-ID: 28332071
Atomic-resolution scanning-transmission electron microscopy showed that barium hexaferrite nanoplatelets display a distinct structure, which represents a novel structural variation of hexaferrites stabilized on the nanoscale. The structure can be presented in terms of two alternating structural blocks stacked across the nanoplatelet: a hexagonal (BaFe6O11)2- R block and a cubic (Fe6O8)2+ spinel S block. The structure of the nanoplatelets usually comprises only two R blocks and always terminates at the basal surfaces with the full S blocks. The structure of a vast majority of the nanoplatelets can be described with a SR*S*RS stacking order, corresponding to a BaFe15O23 composition (bulk hexaferrite has the BaFe12O19 composition). The nanoplatelets display a large, uniaxial magnetic anisotropy with the easy axis perpendicular to the platelet, which is a crucial property enabling different novel applications based on aligning the nanoplatelets with applied magnetic fields, e.g., magneto-mechanical cancer treatment. However, the HF nanoplatelets exhibit a modest saturation magnetization, Ms. Given the cubic S block termination of the platelets, layers of maghemite, gamma-Fe2O3, (M), with a cubic spinel structure, can be easily grown epitaxially on the surfaces of the platelets, forming a sandwiched M/BHF/M platelet structure. The exchange-coupled composite nanoplatelets exhibit a remarkably uniform structure, with an enhanced Ms of more than 50 emu/g while essentially maintaining the out-of-plane easy axis. The enhanced Ms could pave the way for their use in diverse platelet-based magnetic applications.
COBISS.SI-ID: 30880551
Innovative procedure for synthesis of anisotropic superparamagnetic nanostructures was developed in the cooperation with our spin-out company Nanos SCI and published in prestigeous ACS Nano journal. The synthesis is based on dynamic magnetic assembly of superparamagnetic nanoparticle clusters in suspensions into chain-like hierarchical structures and their simultaneous disintegration induced by shear forces of mixing. The procedure is capable of synthesizing magnetic nanochains of defined lengths in larger quantitaties (up to now, similar materials were only synthesized using methods that enable prepration of only small quantities). The nanochains are believed to be important materials especially in magneto-mechanical treatment – they are used in development of new, magneto-mechanical approach of cancer treatment.
COBISS.SI-ID: 28882727
A facile and replicable stepwise chemical method was explored to synthesise magnetically separable Ru-based nanocatalyst. Structural investigation revealed that nanocatalyst is a hierarchical multiphase nanocomposite, consisting of highly magnetic Fe3C (and Fe) nanoparticles, distributed within a high-surface-area graphitic carbonaceous matrix, uniformly decorated with superiorly active catalytic ruthenium nanoparticles and clusters. The nanocatalyst showed an improved catalytic activity and selectivity for the hydro-deoxygenation of bio-resource-related compound eugenol when compared to the commercial Ru/C. In combination with ultrafast magnetic separation, it holds a good emerging potential in the valorisation of renewable resources and recycling of noble metals. The nanocatalyst is synthesised using simple and scalable chemical method without using surfactants and toxic reagents, which demonstrate high catalytic activity and ultrafast magnetic separation.
COBISS.SI-ID: 31457575
In the work, which was conducted during postdoctoral research of our colleague from Srbia and in coopration with researchers form EPFL (Schwitzerland) and Sorbonne University (France), a new simple synthesis route was developed to obtain a nanoscale metastable hard-magnetic epsilon-Fe2O3 phase. The epsilon-Fe2O3 exhibits the highest magnetocrystalline anisotropy among all oxides. Previously, the epsilon-Fe2O3 nanoparticles have only been synthesized inside a silica matrx, which made extraction of pure nanoparticles very difficult. We used annealing of ß-FeOOH (akaganeite) nanorods coated with thin homogeneous silica shell, which can be easily dissolved in base to produce stable colloidal suspensions of the pure nanoparticles. Due to extraordinary magnetic properties and biocompatibility of Fe2O3 these nanoparticles show large potential in for different practical applications.
COBISS.SI-ID: 30606375
The preparation of supramolecular nanostructures was presented in Angewandte Chemie (IF=12.1). The nanostructures were designed by controlled self-assembly of unprotected tripeptides. The achievement proves the expertise of the program group members in the basics of peptide nanotechnology. The peptide nanostructures are further studied within the Program as the model system of amyloid plaques and consequently relevant in the treatment of diseases associated with misfolded proteins such as Alzheimer's disease.
COBISS.SI-ID: 32246567