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Magnetization reversal phenomena (MRP) along magnetic order-order transitions are reported on impurity-doped magnetic systems. The magnetization of (Cr0.70Ti0.30)5S6 are investigated on heating and cooling runs in various magnetic fields, as a typical order-order transition is known to occur on Cr5S6 at a transition temperature T(sub t).

Ultra-thin gold nanowires with uniform diameters of 2 nm and lengths of over 100 μm are synthesized via the reduction of gold(III) chloride in an oleylamine matrix. The gold nanowires, dispersed on an oxidized substrate, are top-contacted with metallic electrodes to manufacture back gated transistors. We investigate the transport properties in the fabricated devices as a function of the gate voltage, the bias voltage, and the temperature. The nonlinear current-bias voltage characteristics from 7 K up to 300 K are well described by the Coulomb blockade model in a nearly one-dimensional quantum dot array (which results from the gold nanowires' thermal fragmentation into a granular material). Our results support a picture in which the electronic transport is governed by sequential tunneling at an applied bias above the global Coulomb blockade threshold, whereas in the Coulomb blockade regime, inelastic cotunneling is dominant up to 70 K, at which point it crosses over to activated behavior. The current dependence on the gate voltage that shows irregular oscillations is well explained by the superimposition of Coulomb oscillation patterns generated by each different dot in the one-dimensional array. We find that the competitive effects of excitation energy and stochastic Coulomb blockade balance the number of current peaks observed. [ABSTRACT FROM AUTHOR]

We investigate ferromagnetism of two-dimensional Pd nanoparticle superlattice by a magnetoresistance measurement. Magnetoresistance increases at a coercive field with hysteretic behavior, which is consistent with the result of a magnetization-field curve. This indicates that the ferromagnetism of the Pd nanoparticle superlattice is electrically detected. From the maximum magnetoresistance change, the conduction-electron polarization of the Pd nanoparticle superlattice is estimated to be ∼4%. The ferromagnetism of Pd nanoparticles is evolved ferromagnetism without protective agents; therefore, the origin of ferromagnetism in the chemically prepared Pd nanoparticles is associated with the intrinsic characteristic of the Pd nanoparticles, but not the effect of the existence of a protective agent. [ABSTRACT FROM AUTHOR]

Faraday rotation spectra of Co nanoparticles embedded in polymethylmethacrylate (PMMA) matrix were investigated by the theoretical and experimental approaches. Co nanoparticles were synthesized by means of the thermal decomposition method, which makes it possible to control the particle concentration without changing the particle size distribution. The amplitude of Faraday rotation is dependent on the particle concentration, and the Faraday rotation spectra show the blueshift accompanied by the decrease in size of Co nanoparticles. The experimental results of Faraday spectra were consistent with the calculation using the Maxwell-Garnett model which is considering the size-dependent free-electron contribution and size independent bound-electron contribution. It was found that the spectral shift was caused only by the size-dependent diagonal element in the dielectric constant tensor, which originates from the confinement of the free electrons in nanoparticles. [ABSTRACT FROM AUTHOR]

Martensite transformation temperature of ferromagnetic shape memory alloy FePd was studied in the shape of nanoparticle and the polycrystalline samples with grain size in micrometers based on the x-ray diffraction and magnetic measurement as a function of sample size. Both the forward transformation start temperature Ms and reverse transformation finish temperature Af of polycrystalline sample monotonically decreased with decreasing grain size and were not observed in the nanoparticles. The size dependence of transformation temperature is explained based on the change in transformation mode, i.e., the decrease in sample size induces the change from the multivariant mode to single variant mode in which the strain energy is large. In the small sample, the strain energy becomes large, and thus the large driving force is required for the transformation. As a result, the large amount of undercooling occurs, which leads to the lowering of Ms. The measurement of heat capacity indicates that the strain energy is elastically stored without dispersion in the transformation process even in the small size because the volume change of FePd at the transformation is very small. The large elastic strain energy works as the driving force to reverse transformation, and then the lowering of Af is induced. Therefore, the lowering of transformation temperature in FePd is characterized by the lowering of thermodynamic equilibrium temperature. [ABSTRACT FROM AUTHOR]

Magnetization reversal phenomena (MRP) along magnetic order-order transitions have recently been reported on impurity-doped magnetic systems. Because imperfect long-range magnetic order exists in these systems, it is expected that a systematic investigation of MRP will give physical information on thermomagnetic processes of magnetic systems in the range from the micro- to nanoscales. As a typical order-order transition (a state doubly modulated by helical and canting orders to a collinear ferrimagnetic state) has been known to occur on Cr5S6 at a transition temperature Tt, we investigate the magnetizations of (Cr0.70Ti0.30)5S6 on heating and cooling runs in various magnetic fields. At 20 Oe, the field-cooled magnetization just below the Curie temperature has a positive sign; the sign turns negative below the compensation temperature TCM (first step) and finally returns to positive below Tt (second step). The first-step MRP observed in this system is explained by the potential barriers resulting from anisotropy energy when the preferred direction of collinear ferrimagnetic moment reverses. The proposed mechanism for second-step MRP is the pinning effect caused by the impurity atoms (Ti) in the helical long-range-order chains. Comparing other examples of MRPs, we discuss the roles of local impurity centers in the thermomagnetic process in magnetic order-order transitions. [ABSTRACT FROM AUTHOR]

(FeyPt100-y)100-xCux nanoparticles with various compositions were synthesized by the simultaneous polyol reduction of Pt(acac)2 and Cu(acac)2 and the thermal decomposition of Fe(CO)5. The as-made particles had a disordered fcc structure and an average diameter of ∼4.8 nm. The result of x-ray diffraction indicated a transformation from fcc structure to fct structure in some samples after annealing at 400 °C for 1 h, and the c/a ratio of lattice constant decreased with increasing Cu content. The doping of Cu clearly plays a significant role on the reduction of the ordering temperature in the ternary (FeyPt100-y)100-xCux alloy. In addition, the ordering of (FeyPt100-y)100-xCux nanoparticles is significantly dependent on the composition of Fe and Pt. As a result, (Fe47Pt53)74Cu26 nanoparticles have the coercive fields of ∼10 and ∼2 kOe at 10 K and room temperature, respectively. [ABSTRACT FROM AUTHOR]

The Faraday rotation in Bi-substitution yttrium-iron garnet thin films, in which Au nanoparticle array is embedded, is analyzed as a function of lattice spacing when compared with the extinction spectra. The studies have shown that Faraday rotation is manipulated by using the wavelength shift of localized surface plasmon resonance that has originated from the change in electromagnetic interaction between Au nanoparticles.

The magnetic properties of B2-type ordered FeRh epitaxial thin films deposited on MgO(001) substrates are described as a function of film thickness. The magnetization data has shown that the ferromagnetic state is more stable than the antiferromagnetic state with decreasing film thickness.

[Fe(sub y)Pt(sub 100-y)](sub 100-x)Cu(sub x) nanoparticles were synthesized by the simultaneous polyol process. The Li(sub 0) ordered phase in the [Fe(sub y)Pt(100-y)](sub 100-x)Cu(sub x) nanoparticles appeared after the annealing at 400 degree Celsius for 1 h.

We report on the effects of postdeposition annealing ambient on the hysteresis observed in the C-V measurement of Al2O3/GeO2 gate-dielectric stacks fabricated on Ge substrates. The results indicate that two types of oxide trap are responsible for the observed hysteresis: a type-I oxide trap that causes persistent C-V hysteresis and a type-II oxide trap that disappears when gate voltage is biased once in the accumulation region. We show that both types of oxide trap reside in the capacitor annealed in O2 ambient, but that only the type-II oxide trap resides in the capacitor annealed in N2 + 10% H2. Time-domain measurements of absorption current suggest that holes injected into the gate-dielectric stack induce the electronic deactivation of the type-II oxide trap. [ABSTRACT FROM AUTHOR]

Magnetization reversal phenomena (MRP) along magnetic order-order transitions have recently been reported on impurity-doped magnetic systems. Because imperfect long-range magnetic order exists in these systems, it is expected that a systematic investigation of MRP will give physical information on thermomagnetic processes of magnetic systems in the range from the micro- to nanoscales. As a typical order-order transition (a state doubly modulated by helical and canting orders to a collinear ferrimagnetic state) has been known to occur on Cr5S6 at a transition temperature Tt, we investigate the magnetizations of (Cr0.70Ti0.30)5S6 on heating and cooling runs in various magnetic fields. At 20 Oe, the field-cooled magnetization just below the Curie temperature has a positive sign; the sign turns negative below the compensation temperature TCM (first step) and finally returns to positive below Tt (second step). The first-step MRP observed in this system is explained by the potential barriers resulting from anisotropy energy when the preferred direction of collinear ferrimagnetic moment reverses. The proposed mechanism for second-step MRP is the pinning effect caused by the impurity atoms (Ti) in the helical long-range-order chains. Comparing other examples of MRPs, we discuss the roles of local impurity centers in the thermomagnetic process in magnetic order-order transitions. [ABSTRACT FROM AUTHOR]