Structure and magnetic properties of bimetallic Ni-Cr nanocrystalline powders

Magnetic properties of NiCr alloys

Abstract: New magnetization measurements on NiCr alloys are reported. At increasing Cr concentrations c less than 11 at%, the mean atomic moment M0 = 0 for c = 12 at% Cr. In the critical concentration range, 11 < c < 15 at% Cr, the experimental data are analysed in terms of the itinerant band model of very weak ferromagnetism. Several characteristic properties related to the effective exchange interaction and to the band structure near the Fermi level are deduced from this analysis. Des mesures d'aimantation d'alliages NiCr ont ete effectuees. Pour c<11% at., on observe une decroissance lineaire du moment magnetique par atome moyen M0 = 0,616 μB – 0,051 c μB. Cette partie lineaire s'extrapole a zero pour c = 12% at. Cr. Les resultats obtenus dans la region critique de disparition du ferromagnetisme, 11 < c <15% at. Cr. ont ete analyses dans un modele d'electron collectif applique au cas du ferromagnetisme tres faible. On en deduit plusieurs proprietes caracteristiques en rapport avec l'interaction d'echange effective et la densite d'etat au niveau de Fermi.

Ni1‐xCrx alloy for self controlled magnetic hyperthermia

Abstract: It is known now that an increase in tumor temperature decreases the tumor resistance to chemo- and radiation therapies. Hyperthermia treatment of the tumor cells where damage to the healthy cells can be avoided is viable by using magnetic nanoparticles with controlled Curie temperatures. Nickel-Chromium (Ni1-xCrx) particles with varying compositions have been investigated as thermoseeds for use in localized self controlled hyperthermia treatment of cancer. A series of Ni1-xCrx alloys, have been prepared to find the specific composition which has Curie temperature around 316-317 K. The samples were cast by arc melting technique, and were annealed at 850 oC for 5 hours in sealed quartz tubes. Magnetic properties of the samples were investigated, including Curie temperature, saturation magnetization and hysterisis using Superconducting Quantum Interference Device (SQUID) and Vibrating Sample Magnetometer (VSM). The Curie temperatures of the alloys were found to decrease almost linearly from 401 K to 289 K as the Cr concentration was increased from x = 4.54 wt% to x = 5.90 wt%. The results showed that Ni1-xCrx alloys might be good candidates for self regulating magnetic hyperthermia applications. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Tuning the onset of ferromagnetism in heterogeneous bimetallic nanoparticles by gas phase doping

Abstract: In the nanoregime, chemical species can reorganize in ways not predicted by their equilibrium bulk behavior. Here, we engineer Ni-Cr nanoalloys at the magnetic end of their compositional range (i.e., 0--15 at. % Cr), and we investigate the effect of Cr incorporation on their structural stability and resultant magnetic ordering. To ensure their stoichiometric compositions, the nanoalloys are grown by cluster beam deposition, a method that allows one-step, chemical-free fabrication of bimetallic nanoparticles. While full Cr segregation toward nanoparticle surfaces is thermodynamically expected for low Cr concentrations, metastability occurs as the Cr dopant level increases in the form of residual Cr in the core region, yielding desirable magnetic properties in a compensatory manner. Using nudged elastic band calculations, residual Cr in the core is explained based on modifications in the local environment of individual Cr atoms. The resultant competition between ferromagnetic and antiferromagnetic ordering gives rise to a wide assortment of interesting phenomena, such as a cluster-glass ground state at very low temperatures and an increase in Curie temperature values. We emphasize the importance of obtaining the commonly elusive magnetic nanophase diagram for $M$-Cr $(M=\mathrm{Fe}$, Co, and Ni) nanoalloys, and we propose an efficient single-parameter method of tuning the Curie temperature for various technological applications.

Synthesis of nanostructured and Ni-Cr3C2 powders by an organic solution reaction method

Abstract: Nanostructured nickel/chromium (NiCr) and nickel-chromium carbide (NiCr3C2) powders were prepared via a chemical route. The technique involves reductive decomposition of an organic solution of metal chloride precursors using sodium triethylborohydride. After co-precipitation of a nanoscale mixed metal (Ni+Cr) powder, low temperature annealing is used to form nanostructured NiCr alloy powder, or low temperature gas phase carburization to form nanostructured Ni-Cr3C2 cermet powder. These powders were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and chemical analysis. The mechanisms of halide reduction and phase formation are discussed.