New Ultra Small Iron-Oxide Nanoparticles with Titanium-Carbamate Coating: Preparation and Magnetic Properties

This work deals with the preparation and chemical characterization of new Ultra-Small Iron-Oxide Superparamagnetic Nanoparticles (USPIONs) functionalized with Titanium-carbamate. The synthesis was performed starting from oleate-coated and 2-pyrrolidone-coated USPIONs having a maghemite ( -Fe2O3) and magnetite (Fe3O4) crystalline core, respectively. Zero-field-cooled (ZFC) and field-cooled (FC) magnetic susceptibility curves as well as the magnetization behavior as a function of temperature are reported and discussed in view of the superparamagnetic properties and coating effect of these new magnetic nanoparticles. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3545

Origin of magnetic moments in carbon nanofoam

A range of carbon nanofoam samples was prepared by using a high-repetition-rate laser ablation technique under various Ar pressures. Their magnetic properties were systematically investigated by dc magnetization measurements and continuous wave (cw) as well as pulsed EPR techniques. In all samples we found very large zero-field cooled-field-cooled thermal hysteresis in the susceptibility measurements extending up to room temperature. Zero-field cooled (ZFC) susceptibility measurements also display very complex behavior with a susceptibility maximum that strongly varies in temperature from sample to sample. Low-temperature magnetization curves indicate a saturation magnetization MS ≈0.35 emu g at 2 K and can be well fitted with a classical Langevin function. MS is more than an order of magnitude larger than any possible iron impurity, proving that the observed magnetic phenomena are an intrinsic effect of the carbon nanofoam. Magnetization measurements are consistent with a spin-glass type ground state. The cusps in the ZFC susceptibility curves imply spin freezing temperatures that range from 50 K to the extremely high value of >300 K. Further EPR measurements revealed three different centers that coexist in all samples, distinguished on the basis of g -factor and relaxation time. Their possible origin and the role in the magnetic phenomena are discussed

Magnetic properties of CuxMn1 x 3[Cr CN 6]2.zH2O complexes

Magnetization measurements were performed on the CuxMn1 x 3[Cr CN 6]2.zH2O molecule based magnets where x 0 0, 0.2, 0.25, 0.3, 0.35 0.4, 0.6, 0.8 and 1.0. Both the Curie temperature and saturated magnetization at first decrease with increasing value of x reaching the minimal value of TC 49 7 K and 0 17 B for x 0 2 and then increase with substitution. The pronounced hysteretic behavior between zero field cooled and field cooled regimes was observed for all samples. Magnetization changes the sign of magnetic polarization in zero field cooled magnetization curve at the compensation temperature Tcomp 16 K for sample with x 0 4. Our results indicate that the system behaves as mixed ferri ferromagnetic syste

Magnetic properties of triangular lattice antiferromagnets Ba3RB9O18 (R = Yb, Er)

Frustration, spin correlations and interplay between competing degrees of freedom are some of the key ingredients that underlie exotic states with fractional excitations in quantum materials. Rare-earth based two dimensional magnetic lattice wherein crystal electric field, spin-orbit coupling, anisotropy and electron correlation between rare-earth moments offer a new paradigm in this context. Herein, we present crystal structure, magnetic susceptibility and specific heat accompanied by crystal electric field calculations on the polycrystalline sample of Ba3RB9O18 (R = Yb, Er) in which R3+ ions form a perfect triangular lattice without anti-site disorder. The localized R3+ spins show neither long-range order nor spin-glass state down to 1.9 K in Ba3RB9O18. Magnetization data reveal a pseudospin Jeff = 1/2 ( Yb3+) in the Kramers doublet state and a weak antiferromagnetic interaction between Jeff = 1/2 moments in the Yb variant. On the other hand, the effective moment {\mu}eff = 8.8 {\mu}B was obtained from the Curie-Weiss fit of the low-temperature susceptibility data of Er variant suggests the admixture of higher crystal electric field states with the ground state. The Curie-Weiss fit of low-temperature susceptibility data for Er system unveils the presence of a relatively strong antiferromagnetic interaction between Er3+ moments compared to its Yb3+ analog. Ba3ErB9O18 does not show long-range magnetic ordering down to 500 mK. Furthermore, our crystal electric field calculations based on magnetization data of Ba3ErB9O18 suggest the presence of a small gap between the ground and first excited Kramers doublets. The broad maximum around 4 K in magnetic specific heat in zero-field is attributed to the thermal population of the first CEF excited state in Ba3ErB9O18, which is consistent with our CEF calculations

Spin amplitude modulation driven magnetoelectic coupling in the new multiferroic FeTe2_2O5_5Br

Magnetic and ferroelectric properties of layered geometrically frustrated cluster compound FeTe$_2$O$_5$Br were investigated with single-crystal neutron diffraction and dielectric measurements. Incommensurate amplitude modulated magnetic order with the wave vector $\bf{q}$=(\half, 0.463, 0) develops below $T_N=10.6(2) {\rm K}$. Simultaneously, a ferroelectric order with the spontaneous polarization perpendicular to ${\bf q}$ and to Fe$^{3+}$ magnetic moments emerges. The observed ferroelectricity and extraordinary linear scaling of the ferroelectric and magnetic order parameter are provoked by the striction of the intercluster Fe-O-Te-O-Fe bridges leading to the shift of Te$^{4+}$ ions and polarization of their lone-pair electrons

Magnetic Properties of Mn-Doped Amorphous SiO2 Matrix

Samples of Mn-doped amorphous SiO2 matrix with manganese concentration 0.7 and 3 at.% have been prepared by a sol-gel method. Transmission electron microscopy analysis has shown that the samples contain agglomerates of amorphous silica particles 10 - 20 nm in size. Two types of Mn-rich particles are dispersed in silica matrix, smaller nanoparticles with dimensions between 3 and 10 nm, and larger crystalline areas consisting of aggregates of the smaller nanoparticles. High-temperature magnetic susceptibility reveals that dominant magnetic phase at higher temperatures is lambda-MnO2. At temperatures below T-C = 43 K strong ferrimagnetism originating from the minor Mn3O4 phase masks the relatively weak magnetism of lambda-MnO2. Magnetic field dependence of the maximum in the zero-field-cooled magnetization for both the samples in the vicinity of 40 K, and a frequency shift of the real component of the AC magnetic susceptibility in the sample with 3 at.% Mn suggest that the magnetic moments of the smaller Mn3O4 nanoparticles with dimensions below 10 nm are subject to thermally activated blocking process just below the Curie temperature T-C. The low-temperature maximum in the zero-field-cooled magnetization observed for both the samples below 10 K indicates possible spin glass freezing of the magnetic moments in the geometrically frustrated Mn sublattice of the lambda-MnO2 crystal structure.12th Annual YUCOMAT Conference, Sep 06-10, 2010, Herceg Novi, Montenegr

Signature of a randomness-driven spin-liquid state in a frustrated magnet

Collective behaviour of electrons, frustration induced quantum fluctuations and entanglement in quantum materials underlie some of the emergent quantum phenomena with exotic quasi-particle excitations that are highly relevant for technological applications. Herein, we present our thermodynamic and muon spin relaxation measurements, complemented by ab initio density functional theory and exact diagonalization results, on the recently synthesized frustrated antiferromagnet Li4CuTeO6, in which Cu2+ ions (S = 1/2) constitute disordered spin chains and ladders along the crystallographic [101] direction with weak random inter-chain couplings. Our thermodynamic experiments detect neither long-range magnetic ordering nor spin freezing down to 45 mK despite the presence of strong antiferromagnetic interaction between Cu2+ moments leading to a large effective Curie-Weiss temperature of -154 K. Muon spin relaxation results are consistent with thermodynamic results. The temperature and magnetic field scaling of magnetization and specific heat reveal a data collapse pointing towards the presence of random-singlets within a disorder-driven correlated and dynamic ground-state in this frustrated antiferromagnet