Denitrogenation process in ThMn12 nitride by in situ neutron powder diffraction

ThMn12 nitrides are good candidates for high performance permanent magnets. However, one of the remaining challenges is to transfer the good properties of the powder into a useful bulk magnet. Thus, understanding the denitrogenation process of this phase is of key importance. In this study, we investigate the magnetic and structural stability of the (Nd0.75, Pr0.25)1.2Fe10.5Mo1.5Nx compound (x=0 and 0.85) as function of temperature by means of neutron powder diffraction. Thermal dependence of the lattice parameters, formation of a-(Fe, Mo), as well as the nitrogen content in the nitrides are investigated by heating the compounds up to 1010 K. The decomposition takes place mainly via the formation of the a-(Fe, Mo) phase, which starts at around 900 K, whereas the nitrogen remains stable in the lattice. Additionally, we show that the magnetic properties of the nitrides [M(4T)=90 Am2/kg and Hc=0.55 T] are maintained after the thermal treatments up to 900 K. This study demonstrates that the ThMn12 nitrides with the Mo stabilizing element offer good prospects for a bulk magnet provided an adequate processing route is found

A Milestone in the Chemical Synthesis of Fe3O4 Nanoparticles Unreported Bulklike Properties Lead to a Remarkable Magnetic Hyperthermia

Among iron oxide phases, magnetite Fe3O4 is often the preferred one for nanotechnological and biomedical applications because of its high saturation magnetization and low toxicity. Although there are several synthetic routes that attempt to reach magnetite nanoparticles NPs , they are usually referred as IONPs iron oxide NPs due to the great difficulty in obtaining the monophasic and stoichiometric Fe3O4 phase. Added to this problem is the common increase of size shape polydispersity when larger NPs D gt; 20 nm are synthesized. An unequivocal correlation between a nanomaterial and its properties can only be achieved by the production of highly homogeneous systems, which, in turn, is only possible by the continuous improvement of synthesis methods. There is no doubt that solving the compositional heterogeneity of IONPs while keeping them monodisperse remains a challenge for synthetic chemistry. Herein, we present a methodical optimization of the iron oleate decomposition method to obtain Fe3O4 single nanocrystals without any trace of secondary phases and with no need of postsynthetic treatment. The average dimension of the NPs, ranging from 20 to 40 nm, has been tailored by adjusting the total volume and the boiling point of the reaction mixture. Mössbauer spectroscopy and DC magnetometry have revealed that the NPs present a perfectly stoichiometric Fe3O4 phase. The high saturation magnetization 93 2 A m2 kg at RT and the extremely sharp Verwey transition at around 120 K shown by these NPs have no precedent. Moreover, the synthesis method has been refined to obtain NPs with octahedral morphology and suitable magnetic anisotropy, which significantly improves the magnetic hyperthemia performance. The heating power of properly PEGylated nano octahedrons has been investigated by AC magnetometry, confirming that the NPs present negligible dipolar interactions, which leads to an outstanding magnetothermal efficiency that does not change when the NPs are dispersed in environments with high viscosity and ionic strength. Additionally, the heat production of the NPs within physiological media has been directly measured by calorimetry under clinically safe conditions, reasserting the excellent adequacy of the system for hyperthermia therapies. To the best of our knowledge, this is the first time that such bulklike magnetite NPs with minimal size shape polydispersity, minor agglomeration, and exceptional heating power are chemically synthesize

Shaping Up Zn Doped Magnetite Nanoparticles from Mono and Bimetallic Oleates The Impact of Zn Content, Fe Vacancies, and Morphology on Magnetic Hyperthermia Performance

The currently existing magnetic hyperthermia treatments usually need to employ very large doses of magnetic nanoparticles MNPs and or excessively high excitation conditions H f gt; 1010 A m s to reach the therapeutic temperature range that triggers cancer cell death. To make this anticancer therapy truly minimally invasive, it is crucial the development of improved chemical routes that give rise to monodisperse MNPs with high saturation magnetization and negligible dipolar interactions. Herein, we present an innovative chemical route to synthesize Zn doped magnetite NPs based on the thermolysis of two kinds of organometallic precursors i a mixture of two monometallic oleates FeOl ZnOl , and ii a bimetallic ironzinc oleate Fe3 amp; 8722;yZnyOl . These approaches have allowed tailoring the size 10 amp; 8722;50 nm , morphology spherical, cubic, and cuboctahedral , and zinc content ZnxFe3 amp; 8722;xO4, 0.05 lt; x lt; 0.25 of MNPs with high saturation magnetization amp; 8805;90 Am2 kg at RT . The oxidation state and the local symmetry of Zn2 and Fe2 3 cations have been investigated by means of X ray absorption near edge structure XANES spectroscopy, while the Fe center distribution and vacancies within the ferrite lattice have been examined in detail through Mo amp; 776;ssbauer spectroscopy, which has led to an accurate determination of the stoichiometry in each sample. To achieve good biocompatibility and colloidal stability in physiological conditions, the ZnxFe3 amp; 8722;xO4 NPs have been coated with high molecular weight poly ethylene glycol PEG . The magnetothermal efficiency of ZnxFe3 amp; 8722;xO4 PEG samples has been systematically analyzed in terms of composition, size, and morphology, making use of the latest generation AC magnetometer that is able to reach 90 mT. The heating capacity of Zn0.06Fe2.94O4 cuboctahedrons of 25 nm reaches a maximum value of 3652 W g at 40 kA m and 605 kHz , but most importantly, they reach a highly satisfactory value 600 W g under strict safety excitation conditions at 36 kA m and 125 kHz . Additionally, the excellent heating power of the system is kept identical both immobilized in agar and in the cellular environment, proving the great potential and reliability of this platform for magnetic hyperthermia therapie

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. Rcp varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02

Mössbauer Study of FeNbCuSiB Mechanical Alloying Process

In the present work we report the preparation of nanocrystalline alloys, of composition Fe73.5Nb3Cu1Si13.5B9, formed directly by mechanical alloying of the constituents. Powders of the pure elements, in the appropriate proportions, were mixed in a Reitch planetary ball mill for upto 120 hours. The composition and the amount of the crystalline phases evolve during the milling and have been followed by Mossbauer Spectroscopy. A metastable FeSi solid solution is-formed with up to 18% Si content. This phase contains about 50% of the Fe present in the sample. At the same time other Fe disordered alloys-are produced. These are characterised by an inhomogeneous distribution of hyperfine fields

Volume expansion contribution to the magnetism of atomically disordered intermetallic alloys.

The origin of magnetism in atomically disordered transition-metal–nonmagnetic i.e., FeAl alloys has been investigated by dichroism and diffraction measurements at high pressure and by band structure calculations. The results show that, in contrast to earlier studies, besides the effects of the local environment of the magnetic ions, disorder-induced lattice changes play a key role in the magnetic properties of these systems. We demonstrate experimentally and theoretically that about 35–45% of the magnetic moment of Fe60Al40 alloys arises from lattice expansion effects induced during the disordering process. Such large effects in Fe60Al40 could actually be related to the moment-volume instability observed in these alloys