Huge Inverse Magnetization Generated by Faraday Induction in Nano-Sized Au@Ni Core@Shell Nanoparticles.

We report on the design and observation of huge inverse magnetizations pointing in the direction opposite to the applied magnetic field, induced in nano-sized amorphous Ni shells deposited on crystalline Au nanoparticles by turning the applied magnetic field off. The magnitude of the induced inverse magnetization is very sensitive to the field reduction rate as well as to the thermal and field processes before turning the magnetic field off, and can be as high as 54% of the magnetization prior to cutting off the applied magnetic field. Memory effect of the induced inverse magnetization is clearly revealed in the relaxation measurements. The relaxation of the inverse magnetization can be described by an exponential decay profile, with a critical exponent that can be effectively tuned by the wait time right after reaching the designated temperature and before the applied magnetic field is turned off. The key to these effects is to have the induced eddy current running beneath the amorphous Ni shells through Faraday induction.

Development of a ferromagnetic component in the superconducting state of Fe-excess Fe1.12Te(1-x)Sex by electronic charge redistribution.

The general picture established so far for the links between superconductivity and magnetic ordering in iron chalcogenide Fe1+y(Te(1-x)Sex) is that the substitution of Se for Te directly drives the system from the antiferromagnetic end into the superconducting regime. Here, we report on the observation of a ferromagnetic component that developed together with the superconducting transition in Fe-excess Fe1.12Te(1-x)Sex crystals using neutron and x-ray diffractions, resistivity, magnetic susceptibility and magnetization measurements. The superconducting transition is accompanied by a negative thermal expansion of the crystalline unit cell and an electronic charge redistribution, where a small portion of the electronic charge flows from around the Fe sites toward the Te/Se sites. First-principles calculations show consistent results, revealing that the excess Fe ions play a more significant role in affecting the magnetic property in the superconducting state than in the normal state and the occurrence of an electronic charge redistribution through the superconducting transition.

Fine structures of self-assembled beta-cyclodextrin/Pluronic in dilute and dense systems: a small angle X-ray scattering study.

The evolution of the fine structures of self-assembled polypseudorotaxane (PPR) in Pluronic (PL F108) solutions containing dilute to dense beta-cyclodextrin (ß-CD) was illustrated for the first time by small angle X-ray scattering (SAXS). Dense ß-CD (∼19 w/v%) was found feasible to be dispersed in 24% citric acid solution. 5% of PL F108 formed cylindrical micelles of 1 nm in radius and 8 nm in length in the presence of 24% citric acid through the dehydration of citric acid and citrate. PPR was formed through host-guest interaction between PL F108 and ß-CD. In dilute ß-CD system (1%), the single chains of PPR with separated ß-CD stacks on PL F108 were formed. The numbers of ß-CD in each stack increased from 1 to 4 on increasing ß-CD concentration to 9%. In a dense ß-CD system, PPR condensed to correlated structures majorly composed of two unit blocks through the hydrogen bonds between PPRs. Two distinguishable correlated domains with correlation lengths of 50 nm (marked α-phase) and 46 nm (marked ß-phase) along the chains, but without fine periodic structure within each individual domain, were identified in the 10% ß-CD solution. Periodic stacking of ß-CD in the domains developed in the 12% solution. As ß-CD concentration increased from 12 to 19%, the correlated heights of α and ß phases reduced from 41 and 32 nm to 30 and 10 nm, respectively. There were 48 ß-CDs that stabilized on each PL F108 chain in the 19% ß-CD system, which is in good agreement with stoichiometry.

Spin polarization and quantum spins in Au nanoparticles.

The present study focuses on investigating the magnetic properties and the critical particle size for developing sizable spontaneous magnetic moment of bare Au nanoparticles. Seven sets of bare Au nanoparticle assemblies, with diameters from 3.5 to 17.5 nm, were fabricated with the gas condensation method. Line profiles of the X-ray diffraction peaks were used to determine the mean particle diameters and size distributions of the nanoparticle assemblies. The magnetization curves M(H(a)) reveal Langevin field profiles. Magnetic hysteresis was clearly revealed in the low field regime even at 300 K. Contributions to the magnetization from different size particles in the nanoparticle assemblies were considered when analyzing the M(H(a)) curves. The results show that the maximum particle moment will appear in 2.4 nm Au particles. A similar result of the maximum saturation magnetization appearing in 2.3 nm Au particles is also concluded through analysis of the dependency of the saturation magnetization M(P) on particle size. The M(P)(d) curve departs significantly from the 1/d dependence, but can be described by a log-normal function. Magnetization can be barely detected for Au particles larger than 27 nm. Magnetic field induced Zeeman magnetization from the quantum confined Kubo gap opening appears in Au nanoparticles smaller than 9.5 nm in diameter.

Short range magnetic correlations induced by La substitution in Ho(1-x)La(x)Mn(2)O(5).

Magnetic susceptibility, x-ray diffraction, neutron diffraction and Raman scattering measurements are employed to study the effects of La substitution on the magnetic properties of multiferroic HoMn(2)O(5). 9% and 18% La-substituted compounds crystallize into the same orthorhombic Pbam symmetry as the parent compound. The magnetic responses to an ac driving magnetic field between 40 and 140 K are greatly enhanced by 18% La substitution. The neutron magnetic diffraction patterns reveal the development of short range magnetic correlations below 140 K. In addition, two Raman peaks and a series of new x-ray diffraction peaks suddenly develop below this temperature. Incommensurate long range antiferromagnetic order appears below 38 K. Magnetic frustration could be the main mechanism governing the present observations.