ε-Fe2O3
213026182
Surface induced reversal of a phase transformation for the synthesis of e Fe2O3 nanoparticles with high coercivity
Abstract A metastable e polymorph of iron(III) oxide (e Fe2O3) is a very attractive material from the technological, engineering, and scientific points of view. In comparison with other iron oxides, it is characterized by unusual magnetic properties and a giant coercivity of ~20 kOe, which is the largest value among metal oxides. The routine method of e Fe2O3 formation is based on the thermal annealing of maghemite (g Fe2O3) nanoparticles confined in a silica matrix where the e Fe2O3 appears as an intermediate phase between the maghemite and an a polymorph (a Fe2O3) hematite (g e a pathway) In this study, it is demonstrated that the e a transformation can be reversed when hematite nanoparticles with an anisotropic hollow morphology are annealed above 600 degC. The observed reversal of the phase stability is explained in terms of an increased nanoparticle surface area and surface energy related to the hollow structure. This study demonstrates the applicability of surface induced phase transformation to stabilize and control e Fe2O3 nanostructures with anisotropic shape and high coercivity ~1600 kA/m that is one of the key properties of functional magnetic materials for information processing and storage. The understanding of e Fe2O3 formation mechanism can provide a new viewpoint and guidance for designing metastable polymorphs and applicative properties.
Marin Tadic Irena Milosevic Slavko Kralj Darko Hanzel Tanja Barudzija Laurence Motte Darko Makovec
216109185
Flexible e Fe2O3 Terephthalate Thin Film Magnets through ALD/MLD
Pliable and lightweight thin film magnets performing at room temperature are indispensable ingredients of the next generation flexible electronics. However, conventional inorganic magnets based on f block metals are rigid and heavy, whereas the emerging organic/molecular magnets are inferior regarding their magnetic characteristics. Here we fuse the best features of the two worlds, by tailoring e Fe2O3 terephthalate superlattice thin films with inbuilt flexibility due to the thin organic layers intimately embedded within the ferrimagnetic e Fe2O3 matrix; these films are also sustainable as they do not contain rare heavy metals. The films are grown with sub nanometer scale accuracy from gaseous precursors using the atomic/molecular layer deposition (ALD/MLD) technique. Tensile tests confirm the expected increased flexibility with increasing organic content reaching a 3 fold decrease in critical bending radius (2.4 0.3 mm) as compared to e Fe2O3 thin film (7.7 0.3 mm) Most remarkably, these hybrid e Fe2O3 terephthalate films do not compromise the exceptional intrinsic magnetic characteristics of the e Fe2O3 phase, in particular the ultrahigh coercive force ~2 kOe) even at room temperature.
ACS applied materials interfaces
Anish Philip Janne-Petteri Niemela Girish Chandra Tewari B Putz Thomas E J Edwards Mitsuru Itoh Ivo Utke Maarit Karppinen
225456897
Magnetic hyperthermia with e Fe2O3 nanoparticles
Biocompatibility restrictions have limited the use of magnetic nanoparticles for magnetic hyperthermia therapy to iron oxides, namely magnetite (Fe3O4) and maghemite (g Fe2O3) However, there is yet another magnetic iron oxide phase that has not been considered so far, in spite of its unique magnetic properties: e Fe2O3. Indeed, whereas Fe3O4 and g Fe2O3 have a relatively low magnetic coercivity, e Fe2O3 exhibits a giant coercivity. In this report, the heating power of e Fe2O3 nanoparticles in comparison with g Fe2O3 nanoparticles of similar size ~20 nm) was measured in a wide range of field frequencies and amplitudes, in uncoated and polymer coated samples. It was found that e Fe2O3 nanoparticles primarily heat in the low frequency regime (20 100 kHz) in media whose viscosity is similar to that of cell cytoplasm. In contrast, g Fe2O3 nanoparticles heat more effectively in the high frequency range (400 900 kHz) Cell culture experiments exhibited no toxicity in a wide range of nanoparticle concentrations and a high internalization rate. In conclusion, the performance of e Fe2O3 nanoparticles is slightly inferior to that of g Fe2O3 nanoparticles in human magnetic hyperthermia applications. However, these e Fe2O3 nanoparticles open the way for switchable magnetic heating owing to their distinct response to frequency.
Yuanyu Gu Marie Yoshikiyo Asuka Namai Debora Bonvin Rafael Pinol Pedro Tellez Nuno J O Silva Fredrik Ahrentorp Christer Johansson Joaquin Marco-Brualla Raquel Moreno-Loshuertos Patricio Fernandez-Silva Yuwen Cui Shin-ichi Ohkoshi Angel Millan
225643174
A facile synthesis of novel e Fe2O3 grafted 2D h BN nanostructures for enhanced visible active photocatalytic applications
Novel nanostructures of h BN and e Fe2O3 grafted h BN (h BN/e Fe2O3) have been synthesized by solvothermal method. The prepared h BN/e Fe2O3 nanostructures are highly reproducible. XRD analysis confirmed the phase and crystal structure of synthesized h BN and h BN/e Fe2O3 nanostructures. The sheet like morphology of the nanostructured h BN and h BN/e Fe2O3 are confirmed by SEM, TEM and HRTEM analyses. Moreover, the uniform distributions of e Fe2O3 on the surface of h BN nanosheets are confirmed by SEM and TEM images. FT IR and Raman studies are used to identify the functional groups and structure of h BN and h BN/e Fe2O3 nanostructures. The optical absorption spectra show a clear red shift in the h BN/e Fe2O3 nanostructure compared to pure h BN nanosheets which shows the electronic band structure modification in BN caused by grafting of e Fe2O3 nanoparticles onto the surface of h BN. The chemical composition of prepared h BN/e Fe2O3 heterostructure is analyzed by XPS. The photo oxidative performance of pure h BN and h BN/e Fe2O3 nanostructure has been studied for oxidative decomposition of formic acid under visible light irradiation. The h BN/e Fe2O3 nanostructure showed relatively high photo oxidative performance compared to pure h BN.
Durai Mani Durai Mathivanan Ho Chang Kumaravel Sakthivel E Elangovan Thiripuranthagan Sivakumar Mukannan Arivanandhan Ramasamy Jayavel
219037016
Millimeter sized flower like clusters composed of mullite and e Fe2O3 on the Hare's Fur Jian Ware
Abstract Porcelain that contains micrometer sized e Fe2O3, a promising advanced material with unique magnetic properties, has received growing attention these years. Herein, we discovered millimeter sized unprecedented mullite e Fe2O3 clusters organized in a flower like manner blooming on the Hare's Fur Jian ware of the Song dynasty (960 1279 A.D. They are composed of branches radiating from the center, petals growing along the branches, needles on both sides of the petals and reflective platforms distributed all over the flower. After a series of microscopic and spectroscopic characterizations, mullite and e Fe2O3 were identified to be the main components, and a possible growth process was proposed. The residual quartz in the glaze, the relatively thin glaze on the edge of the bowl and the reducing firing environment were considered to be the main factors for its formation. These results provide a novel access toward the ancient ceramic technologies and inspirations on refractory mullite and magnetic material e Fe2O3.
Qianying Hoo Yihao Liang Xinlong Yan Xiaohu Wang Tiewa Cao Xue-wei Cao
219463431
Synthesis and magnetic properties of e Fe2O3 by ball milling and post annealing
Abstract A novel method for synthesizing e Fe2O3 nanoparticles was proposed. The e Fe2O3 nanoparticles were prepared by ball milling of Iron(III) nitrate nonahydrate and hydrophilic vapor phase nano silica and post annealing. The structure, morphology and magnetic properties of the prepared nanoparticles were studied by X ray diffraction, Raman spectroscopy, transmission electron microscopy, and magnetic measurements. The results show that the average particle size and magnetic properties of the e Fe2O3 nanoparticles can be controlled by the relative amount of Iron(III) nitrate nonahydrate used. With the increase of the amount of Iron(III) nitrate nonahydrate, the e Fe2O3 nanoparticle size increases. And the coercivity of the e Fe2O3 nanoparticles increases. The magnetic hysteresis loops of the e Fe2O3 nanoparticles show clear shifts along the magnetic field axis at 300 K, after the nanoparticles were warmed from low temperature in a magnetic field of 50 kOe. This observation is explained in term of exchange bias effect.
Yuhang Zhao Gehui Wen
226764859
Heterostructures of e Fe2O3 and a Fe2O3: insights from density functional theory
Many materials used in energy devices or applications suffer from the problem of electron hole pair recombination. One promising way to overcome this problem is the use of heterostructures in place of a single material. If an electric dipole forms at the interface, such a structure can lead to a more efficient electron hole pair separation and thus prevent recombination. Here we model and study a heterostructure comprised of two polymorphs of Fe2O3. Each one of the two polymorphs, a Fe2O3 and e Fe2O3, individually shows promise for applications in photoelectrochemical cells. The heterostructure of these two materials is modeled by means of density functional theory. We consider both ferromagnetic as well as anti ferromagnetic couplings at the interface between the two systems. Both individual oxides are insulating in nature and have an anti ferromagnetic spin arrangement in their ground state. The same properties are found also in their heterostructure. The highest occupied electronic orbitals of the combined system are localized at the interface between the two iron oxides. The localization of charges at the interface is characterized by electrons residing close to the oxygen atoms of e Fe2O3 and electron holes localized on the iron atoms of a Fe2O3, just around the interface. The band alignment at the interface of the two oxides shows a type III broken band gap heterostructure. The band edges of a Fe2O3 are higher in energy than those of e Fe2O3. This band alignment favours a spontaneous transfer of excited photo electrons from the conduction band of a to the conduction band of e Fe2O3. Similarly, photo generated holes are transferred from the valence band of e to the valence band of a Fe2O3. Thus, the interface favours a spontaneous separation of electrons and holes in space. The conduction band of e Fe2O3, lying close to the valence band of a Fe2O3, can result in band to band tunneling of electrons which is a characteristic property of such type III broken band gap heterostructures and has potential applications in tunnel field effect transistors.
Imran Ahamed Nicola Seriani Ralph Gebauer Arti Kashyap
225554369
Heterostructures of e Fe2O3 and a Fe2O3: insights from density functional theory
Many materials used in energy devices or applications suffer from the problem of electron hole pair recombination. One promising way to overcome this problem is the use of heterostructures in place of a single material. If an electric dipole forms at the interface, such a structure can lead to a more efficient electron hole pair separation and thus prevent recombination. Here we model and study a heterostructure comprised of two polymorphs of Fe2O3. Each one of the two polymorphs, a Fe2O3 and e Fe2O3, individually shows promise for applications in photoelectrochemical cells. The heterostructure of these two materials is modeled by means of density functional theory. We consider both ferromagnetic as well as anti ferromagnetic couplings at the interface between the two systems. Both individual oxides are insulating in nature and have an anti ferromagnetic spin arrangement in their ground state. The same properties are found also in their heterostructure. The highest occupied electronic orbitals of the combined system are localized at the interface between the two iron oxides. The localization of charges at the interface is characterized by electrons residing close to the oxygen atoms of e Fe2O3 and electron holes localized on the iron atoms of a Fe2O3, just around the interface. The band alignment at the interface of the two oxides shows a type III broken band gap heterostructure. The band edges of a Fe2O3 are higher in energy than those of e Fe2O3. This band alignment favours a spontaneous transfer of excited photo electrons from the conduction band of a to the conduction band of e Fe2O3. Similarly, photo generated holes are transferred from the valence band of e to the valence band of a Fe2O3. Thus, the interface favours a spontaneous separation of electrons and holes in space. The conduction band of e Fe2O3, lying close to the valence band of a Fe2O3, can result in band to band tunneling of electrons which is a characteristic property of such type III broken band gap heterostructures and has potential applications in tunnel field effect transistors.
Imran Ahamed Nicola Seriani Ralph Gebauer Arti Kashyap
216275051
Born effective charges and electric polarization in bulk e Fe2O3: An ab initio approach
Abstract Limitation in the synthesis of single crystal has restricted the complete understanding of the magnetoelectric properties of bulk e Fe2O3. In order to understand the electric polarization of bulk e Fe2O3, we have employed a first principles Berry phase method and the density functional perturbation theory to calculate the spontaneous electric polarization and Born effective charges (BECs) of e Fe2O3. The polarization quanta of the ferroelectric bulk e Fe2O3 and its polarization lattice are also reported. The polarization switching through a paraelectric transition phase of a low barrier is found to be favorable. The polarization and BECs calculated by both methods are in good agreement.
Imran Ahamed Ralph Skomski Arti Kashyap
213180618
Modulating the Structure and Magnetic Properties of e Fe2O3 Nanoparticles via Electrochemical Li+ Insertion.
e Fe2O3, a metastable phase of iron oxide, is widely known as a room temperature multiferroic material or as a superhard magnet. Element substitution into e Fe2O3 has been reported in the literature; however, the substituted ions have a strong site preference depending on their ionic radii and valence. In this study, in order to characterize the crystal structure and magnetic properties of e Fe2O3 in the Fe2+/Fe3+ coexisting states, Li+ was electrochemically inserted into e Fe2O3 to reduce Fe3+ The discharge and charge of Li+ into/from e Fe2O3 revealed that Li+ insertion was successful. X ray magnetic circular dichroism results indicated that the reduced Fe did not exhibit site preference. Increasing the Li+ content in e Fe2O3 resulted in decreased saturation magnetization and irregular variation of the coercive field. We present a comprehensive discussion of how magnetic properties are modified with increasing Li+ content using transmission electron microscopy images and considering the Li+ diffusion coefficient. The results suggest that inserting Li+ into crystalline e Fe2O3 is a useful tool for characterizing crystal structure, lithiation limit, and magnetic properties in the coexistence of Fe2+/Fe3+
Inorganic chemistry
Sou Yasuhara Yosuke Hamasaki Tsukasa Katayama Takahiro Ao Yoshiyuki Inaguma Hajime Hojo Maarit Karppinen Anish Philip Shintaro Yasui Mitsuru Itoh