Materials research has driven the development of modern nano-electronic devices. In particular, research in magnetic thin films has revolutionized the development of spintronic devices1,2 because identifying new magnetic materials is key to better device performance and design. Van der Waals crystals retain their chemical stability and structural integrity down to the monolayer and, being atomically thin, are readily tuned by various kinds of gate modulation3,4. Recent experiments have demonstrated that it is possible to obtain two-dimensional ferromagnetic order in insulating Cr2Ge2Te6 (ref. 5) and CrI3 (ref. 6) at low temperatures. Here we develop a device fabrication technique and isolate monolayers from the layered metallic magnet Fe3GeTe2 to study magnetotransport. We find that the itinerant ferromagnetism persists in Fe3GeTe2 down to the monolayer with an out-of-plane magnetocrystalline anisotropy. The ferromagnetic transition temperature, Tc, is suppressed relative to the bulk Tc of 205 kelvin in pristine Fe3GeTe2 thin flakes. An ionic gate, however, raises Tc to room temperature, much higher than the bulk Tc. The gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2 opens up opportunities for potential voltage-controlled magnetoelectronics7-11 based on atomically thin van der Waals crystals.

Gate-tunable Room-temperature Ferromagnetism in Two-dimensional Fe 3 GeTe 2

Magnetoresponsive Therapy Nohyun Lee, Dongwon Yoo, Daishun Ling,†,‡,⊥ Mi Hyeon Cho, Taeghwan Hyeon,*,†,‡ and Jinwoo Cheon* †Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul 151-742, Korea ‡School of Chemical and Biological Engineering, Seoul National University, Seoul 151-742, Korea Department of Chemistry, Yonsei University, Seoul 120-749, Korea School of Advanced Materials Engineering, Kookmin University, Seoul 136-702, Korea Institute of Pharmaceutics, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, PR China

Iron Oxide Based Nanoparticles for Multimodal Imaging and Magnetoresponsive Therapy.

Spinel ferrite magnetic adsorbents: Alternative future materials for water purification?

Preface. Contents of volumes 1-6. 1. Magnetism in ultrathin transition metal films (U. Gradmann). 2. Energy band theory of metallic magnetism in the elements (V.L. Moruzzi, P.M. Marcus). 3. Density functional theory of the ground state magnetic properties of rare earths and actinides (M.S.S. Brooks, B. Johansson). 4. Diluted magnetic semiconductors (J. Kossut, W. Dobrowolski). 5. Magnetic properties of binary rare-earth 3d-transition-metal intermetallic compounds (J.J.M. Franse, R.J. Radwanski). 6. Neutron scattering on heavy fermion and valence fluctuation 4f-systems (M. Loewenhaupt, K.H. Fischer). Author index. Subject index. Materials index.

Handbook of Magnetic Materials

Review on magnetic nanoparticles for magnetic nanofluid hyperthermia application

An efficient magnetic resonance imaging (MRI) contrast agent with a high R2 relaxivity value is achieved by controlling the shape of iron oxide to rod like morphology with a length of 30–70 nm and diameter of 4–12 nm. Fe3O4 nanorods of 70 nm length, encapsulated with polyethyleneimine show a very high R2 relaxivity value of 608 mM−1 s−1. The enhanced MRI contrast of nanorods is attributed to their higher surface area and anisotropic morphology. The higher surface area induces a stronger magnetic field perturbation over a larger volume more effectively for the outer sphere protons. The shape anisotropy contribution is understood by calculating the local magnetic field of nanorods and spherical nanoparticles under an applied magnetic field (3 Tesla). As compared to spherical geometry, the induced magnetic field of a rod is stronger and hence the stronger magnetic field over a large volume leads to a higher R2 relaxivity of nanorods.

/pdf/iron-oxide-nanorods-as-high-performance-magnetic-resonance-2t0zykocb8.pdf

Iron oxide nanorods as high-performance magnetic resonance imaging contrast agents.

Engineered magnetic nanoparticles, MFe2O4 (where M = Mn, Fe, Co, Ni and Zn), of mean size 2–16 nm (standard deviation σ ≤ 15%) with controlled magnetic properties have been synthesized through a solventless thermolysis technique. In this ‘energy-efficient’ facile approach, a long-chain amine is utilized as the solvent, reducing and surface-functionalizing agent. The particle sizes between 2–9 nm are tuned by simple manipulation of the amine to precursor molar ratio while the larger sizes (12–16 nm) are attained by seed-mediated growth. The synthesized nanoparticles are magnetic and show cubic-spinel structure as characterized by HRTEM, SAED, XRD and Raman spectroscopy. The spin–orbit coupling, which induces larger magnetocrystalline anisotropy energy, leads to an increase of the blocking temperature in an order of Zn, Ni, Mn, Fe and Co. Additionally the saturation magnetization (magnetization at 2 T) of nanoparticle decreases in an order as per the periodic arrangement i.e. Mn > Fe > Co > Ni > Zn. This trend is better understood in terms of a cationic distribution of varying magnetic moments in these spinel oxides. For all the ferrites, the magnetization saturates to the bulk value at sizes ≥12 nm, indicating strict control over the dead layer thickness. The effect of surface coordination on the magnetic properties of the ferrite nanoparticles is analyzed. In contrast to trioctylphosphine oxide (TOPO) and oleic acid (OA) functionalized nanoparticles the saturation magnetization of amine protected nanoparticles is higher, which suggests a strong coupling of amine molecules to cations at the particle interface.

Surface controlled synthesis of MFe2O4 (M = Mn, Fe, Co, Ni and Zn) nanoparticles and their magnetic characteristics

We observed Verwey transition in very small (6–14 nm) amine-coated octahedral magnetite (Fe3O4) nanoparticles that is not present in spherical similarly sized (4–13 nm) nanoparticles. Electron microscopy shows that octahedral nanoparticles have {111} facets with better cationic coordination symmetry as their surface. Spherical shape illustrates conventional superparamagnetic behavior; on the contrary, a characteristic Verwey transition near 120 K is prominent in field-cooled/zero-field-cooled curves of octahedral nanoparticles. Higher saturation magnetization in octahedral nanoparticles indicates lesser surface spin disorder and well-established anisotropy. Better surface coordination offers a reduced number of oxygen vacancies at the surface and, therefore, better stoichiometry results in a Verwey transition in octahedral nanoparticles. Electrical resistivity measurements show a sharp change in resistance for octahedral particles below the Verwey transition temperature which is completely hindered in sph...

Verwey Transition in Ultrasmall-Sized Octahedral Fe3O4 Nanoparticles

Enzymatic and non-enzymatic electrochemical glucose sensor based on carbon nano-onions

We present here the multitasking capabilities of Ag-embedded ZnO nanocomposites (Ag–ZnO NCs), which include the photocatalytic degradation of organic dyes, bacterial inhibition, and cancer therapeutics. Ag-embedded ZnO nanocomposites (Ag–ZnO NCs) of mesoporous spherical morphology (size ∼ 150 ± 50 nm) are successfully synthesized by a facile and single step soft-chemical approach. To understand the effect of Ag loading on multitasking properties, Ag–ZnO NCs are synthesized with different wt% of Ag. It was found that Ag5-ZnO NCs (5 wt% of Ag) showed excellent solar light-induced photocatalytic degradation properties against both cationic as well as anionic dyes. In addition, the presence of Ag in these NCs makes them strongly antibacterial, and kills 100% Escherichia coli (E. coli) cells within 2 hours (under dark), and within 30 min (under solar light). The enhanced photocatalytic and antibacterial activity of Ag–ZnO NCs is due to the anchoring of Ag NPs onto ZnO as well as minor substitution of Ag ions in the lattice of ZnO. This produces abundant charge carriers and generates significantly enhanced reactive oxygen species (ROS), which seem responsible for the multitasking properties. Furthermore, the cytotoxic study shows that Ag5-ZnO NCs kill oral carcinoma (KB) cells under visible light irradiation, and work as photosensitizers towards the photodynamic therapy of cancer due to the excellent photocatalytic activity. The high ROS concentration depolarizes the mitochondrial membrane potential, which in turn initiates apoptosis in oral carcinoma (KB) cells inducing cell death. Therefore, the as-prepared mesoporous Ag–ZnO NCs show great promise in waste water treatment, and cancer therapeutics.

Visible light driven mesoporous Ag-embedded ZnO nanocomposites: reactive oxygen species enhanced photocatalysis, bacterial inhibition and photodynamic therapy

Jeotikanta Mohapatra

Papers

Iron oxide nanorods as high-performance magnetic resonance imaging contrast agents.

Surface controlled synthesis of MFe2O4 (M = Mn, Fe, Co, Ni and Zn) nanoparticles and their magnetic characteristics

Verwey Transition in Ultrasmall-Sized Octahedral Fe3O4 Nanoparticles

Enzymatic and non-enzymatic electrochemical glucose sensor based on carbon nano-onions

Visible light driven mesoporous Ag-embedded ZnO nanocomposites: reactive oxygen species enhanced photocatalysis, bacterial inhibition and photodynamic therapy