Search results for "Spontaneous magnetization"
showing 10 items of 15 documents
Interplay between Chemical Composition and Cation Ordering in the Magnetism of Ni/Fe Layered Double Hydroxides
2013
We report the synthesis of a family of ferrimagnetic NiFe layered double hydroxides (LDHs) with a variable Ni(2+)/Fe(3+) in-plane composition of [Ni(1-x)Fe(x)(OH)2](CO3)(x/2)·yH2O (x = 0.20, 0.25, and 0.33) by following a modified homogeneous precipitation. These layered magnets display high crystallinity, homogeneous hexagonal morphologies, and micrometric size that enable their quantitative exfoliation into single layers by sonomechanical treatment of the solids in polar solvents. This was confirmed by dynamic light scattering, UV-vis spectroscopy, high-resolution transmission electron miscroscopy, and atomic force microscopy methodologies to study the resulting steady suspensions. Our ma…
Room Temperature Magnetism in Layered Double Hydroxides due to Magnetic Nanoparticles
2013
Some recent reports claiming room temperature spontaneous magnetization in layered double hydroxides (LDHs) have been published; however, the reported materials cause serious concern as to whether this cooperative magnetic behavior comes from extrinsic sources, such as spinel iron oxide nanoparticles. The syntheses of crystalline Fe(3+)-based LDHs with and without impurities have been developed, highlighting the care that must be taken during the synthetic process in order to avoid misidentification of magnetic LDHs.
Pressure induced increase in Tc for the organic-based magnet FeII(TCNE)2 (TCNE=tetracyanoethylene)
2013
Abstract Pressure dependent magnetization and 57Fe Mossbauer studies were performed on Fe(TCNE)[C4(CN)8]1/2·zCH2Cl2 (TCNE = tetracyanoethylene). Pressure did not influence the Mossbauer parameters in paramagnetic state. Mossbauer data reveals the onset of magnetic ordering at 130 K and significant enhancement of the magnetic ordering temperature from 100 to 150 K accompanied by an increase of the spontaneous magnetization, which is higher than reported from the magnetic data, and application of pressure induces the reversible formation of a new, metastable magnetic species. These changes suggest an increase of the dimensionality of magnetic interaction, i.e., stronger interlayer coupling. A…
High field magnetization of the colloidal Mn–Zn ferrite
1999
Abstract The magnetic properties of a hydrocarbon based colloid (stabilized by oleic acid) of polydisperse chemically co-precipitated Mn 0.5 Zn 0.5 Fe 2 O 4 particles are discussed in the paper. Two fractions are separated from an initial ferrofluid sample by centrifugation. X-ray diffraction measurements show the crystal structure of the particles and a broadened shape of the diffraction lines. Mean particle diameters 6.2 nm (the light fraction) and 9.7 nm (the heavy one) were determined by TEM measurements. The magnetization of the colloids is measured by VSM up to 12 T. A significant slope in the magnetization curves in the high field region is displayed for both samples in the temperatu…
The Missing Link in the Magnetism of Hybrid Cobalt Layered Hydroxides: The Odd‐Even Effect of the Organic Spacer
2021
A dramatic change in the magnetic behaviour, which solely depends on the parity of the organic linker molecules, has been found in a family of layered CoII hydroxides covalently functionalized with dicarboxylic molecules. These layered hybrid materials have been synthesized at room temperature using a one-pot procedure through the epoxide route. While hybrids connected by odd alkyl chains exhibit coercive fields (Hc) below ca. 3500 Oe and show spontaneous magnetization at temperatures (TM) below 20 K, hybrids functionalized with even alkyl chains behave as hard magnets with Hc>5500 Oe and display a TM higher than 55 K. This intriguing behaviour was studied by density functional theory with …
Magnetic properties and61Ni Mössbauer spectroscopy of the ternary phosphide CrNiP
2008
The results of x-ray diffraction, dc magnetization, and 61Ni Mossbauer spectroscopy studies of the ternary phosphide CrNiP are reported. This compound crystallizes in the orthorhombic Co2P-type structure (space group Pnma) with the lattice parameters a = 5.7965(1) A, b = 3.5337(1) A, and c = 6.8123(2) A. NiCrP is a ferromagnet with Curie temperature TC = 135.1(1) K. The ferromagnetic-to-paramagnetic transition is characterized by the critical exponents β = 0.355(22), γ = 1.241(18), and δ = 4.585(20). Their values are close to those of a 3D Heisenberg ferromagnet. The temperature dependence of the magnetic susceptibility above TC follows the modified Curie–Weiss law with a paramagnetic Curie…
Spontaneous Magnetization in Heterometallic NiFe-MOF-74 Microporous Magnets by Controlled Iron Doping
2017
We report the direct synthesis of mixed-metal NiFe-MOF-74 solids that display combination of porosity with ferrimagnetic ordering. Compared to the undoped Ni phase, controlled doping with Fe enables to modify intra and interchain magnetic interactions for the onset of spontaneous magnetization at temperatures fixed by the doping level. Synthesis of porous magnets remains somewhat elusive due to the difficulties in isolating foreseeable metal-organic architectures that combine small bridging linkers, for strong magnetic coupling, with polyaromatic connectors responsible for porosity. In turn, we demonstrate that metal doping is better fitted to modify the magnetism of Metal-Organic Framework…
Influence of morphology in the magnetic properties of layered double hydroxides
2018
We report the controlled synthesis of magnetic CoAl and NiFe layered double hydroxides (LDHs) endowed with well-defined morphology (hexagonal and flower-like shapes) by means of modified homogeneous precipitation. These layered magnets display high crystallinity and micrometric size, thus offering a perfect scenario for the elucidation of the role exerted by distortion of the layers in their magnetic behaviour. The magnetic properties have been investigated by means of DC and AC magnetic susceptibility measurements and isothermal magnetization, demonstrating that the distortion of the nanosheets induces a magnetically more disordered behaviour, with marked spin-glass nature, independently o…
Hybrid Molecular Magnets Obtained by Insertion of Decamethylmetallocenium Cations into Layered, Bimetallic Oxalate Complexes: [ZIIICp*2][MIIMIII(ox)3…
2000
A new series of hybrid organometallic - inorganic layered magnets with the formula [Z(III)Cp*2][M(II)M(III)(ox)3] (Z(III) = Co, Fe; M(III) = Cr, Fe; M(II) = Mn, Fe, Co, Cu, Zn; ox = oxalate; Cp* = pentamethylcyclopentadienyl) has been prepared. All of these compounds are isostructural and crystallize in the monoclinic space group C2/m, as found by X-ray structure analysis. Their structure consists of an eclipsed stacking of the bimetallic oxalate-based extended layers separated by layers of organometallic cations. These salts show spontaneous magnetization below To, which corresponds to the presence of ferro-, ferri-, or canted antiferromagnetism. Compounds in which the paramagnetic deca-me…
Electronic structure of quantum dots
2002
The properties of quasi-two-dimensional semiconductor quantum dots are reviewed. Experimental techniques for measuring the electronic shell structure and the effect of magnetic fields are briefly described. The electronic structure is analyzed in terms of simple single-particle models, density-functional theory, and "exact" diagonalization methods. The spontaneous magnetization due to Hund's rule, spin-density wave states, and electron localization are addressed. As a function of the magnetic field, the electronic structure goes through several phases with qualitatively different properties. The formation of the so-called maximum-density droplet and its edge reconstruction is discussed, and…