Search

The proximity effects of the Pt layers on the magnetic properties of the ultrathin Y3Fe5O12 (YIG) films have been systematically investigated. A significant decrease in the saturation magnetization is observed after capping the Pt films on the YIG films, indicating that a strong interaction occurs between Pt and YIG. In contrast, the magnetic properties remain essentially unchanged for YIG capping with the Cu films. The X-ray magnetic circular dichroism measurements show that a selective charge transfer occurs from Pt to the tetrahedral site Fe of YIG, leading to a reduction of the magnetic moment of the interfacial YIG. Our findings provide important clues to further understanding the pure spin current transport at the Pt/YIG interface. [ABSTRACT FROM AUTHOR]

Rare earth doping is an important approach to improve the desired properties of high-k gate dielectric oxides. We have carried out a comprehensive theoretical investigation on the phase stability, band gap, formation of oxygen vacancies, and dielectric properties for the Gd-doped HfO2. Our calculated results indicate that the tetragonal phase is more stable than the monoclinic phase when the Gd doping concentration is greater than 15.5%, which is in a good agreement with the experimental observations. The dopant's geometric effect is mainly responsible for the phase stability. The Gd doping enlarges the band gap of the material. The dielectric constant for the Gd-doped HfO2 is in the range of 20-30 that is suitable for high-k dielectric applications. The neutral oxygen vacancy formation energy is 3.2 eV lower in the doped material than in pure HfO2. We explain the experimental observation on the decrease of photoluminescence intensities in the Gd-doped HfO2 according to forming the dopant-oxygen vacancy complexes. [ABSTRACT FROM AUTHOR]

Nanoscale Fe3O4 epitaxial thin film has been synthesized on MgO/GaAs(100) spintronic heterostructure, and studied with X-ray magnetic circular dichroism. We have observed a total magnetic moment (ml+s) of (3.32±0.1)μB/f.u., retaining 83% of the bulk value. Unquenched orbital moment (ml) of (0.4760.05)lB/f.u. has been confirmed by carefully applying the sum rule. The results offer direct experimental evidence of the bulk-like total magnetic moment and a large orbital moment in the nanoscale fully epitaxial Fe3O4/MgO/GaAs(100) heterostructure, which is significant for spintronics applications. [ABSTRACT FROM AUTHOR]

For L10 FePt films, the anomalous Hall conductivity σxy=-aσxx-b, where a=a0f(T), b=b0f(T), and f(T) is the temperature dependence factor of the spontaneous magnetization. With increasing chemical long range ordering S, a0 changes its sign accompanied by a reduction of its magnitude and b0 increases monotonically. The spin-orbit coupling strength is suggested to increase with increasing S. As an approach, the long range chemical ordering can be used to control the anomalous Hall effect in ferromagnetic alloy films. [ABSTRACT FROM AUTHOR]

Ultrafast spin dynamics has for the first time been studied in perpendicular magnetized granular films. For FePt continuous films and FePt–MgO and FePt–Ag granular films with femtosecond laser excitations, the coercivity HC and the saturation Kerr rotation θKS are dramatically reduced, accompanied by a sharp increase in the reflectivity R. Afterward, these physical quantities are slowly recovered. The changes in HC, θKS, and R are all different among FePt, FePt–MgO, and FePt–Ag films. The difference is caused by different film thicknesses and in particular by the surface plasmon resonance of metallic nanoparticles. [ABSTRACT FROM AUTHOR]

A large reversible magnetocaloric effect has been observed in Tb3Co compound. Under a magnetic field change of 5 T, the maximum value of magnetic entropy change ΔSM is -18 J kg-1 K-1 at 84 K and the relative cooling power is 738 J kg-1 with no hysteresis loss. In particular, the large reversible ΔSMmax, -8.5 J kg-1 K-1, is achieved for a low magnetic field change of 2 T. The magnetic anisotropy and the texture of the material greatly affect ΔSM. The large reversible magnetocaloric effect (both the large ΔSM and the high relative cooling power) indicates that Tb3Co could be a promising candidate for magnetic refrigeration. [ABSTRACT FROM AUTHOR]

In Fe0.8Mn1.5As compound, an external magnetic field induces a metamagnetic transition from an antiferromagnetic phase to a ferrimagnetic phase above Ts=285 K, leading to large magnetocaloric effects around room temperature. Instead of showing inverse magnetocaloric effects, the sign of the entropy change ΔSM in the compound is unexpectedly negative, revealing a different mechanism. The maximum value of ΔSM is 6.2 J/kg K at 287.5 K for a magnetic field change of 5 T. The study on systems with antiferromagnetism-related metamagnetic transitions may open an important field in searching good materials for room-temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]

The magnetic phase transition and magnetocaloric effect are investigated on [variant_greek_epsilon]-(Mn0.83Fe0.17)3.25Ge compound. A large positive magnetic entropy change ΔSM is observed, which is accompanied with a field-induced metamagnetic transition from a collinear to a triangular antiferromagnetic configuration in this antiferromagnetic compound. The maximum value of ΔSM is 11.6 J/kg K at 93 K for a magnetic field change of 7 T. The study on systems with antiferromagnetic phases may open an important field in searching new materials for magnetic refrigeration. [ABSTRACT FROM AUTHOR]

An axial first-order gradiometer is formed by coupling the input coil of a flexible high-temperature superconducting flux transformer inductively to a directly coupled superconducting quantum interference device magnetometer. The transformer is patterned in a single-layer YBa2Cu3O7-x film on a flexible Hastelloy tape. The tape is bent such flint file two outer pickup loops of the transformer are facing each other while perpendicular to the magnetometer plane resulting in a gradiometer baseline of 35 mm. A superconducting shield is mechanically adjusted to reduce file gradiometer response to uniform fields applied perpendicularly to both file magnetometer plane and file plane of the transformer pickup loops, by a factor of typically 7000. [ABSTRACT FROM AUTHOR]

Exchange-coupled wedged-permalloy/uniform-FeMn bilayers are studied by ferromagnetic resonance and magnetometry measurements with applied field parallel to the film plane. An additional weak resonance peak was observed besides an intense resonance, indicating the existence of interfacial diffusion. For all samples, the exchange field measured by the ferromagnetic resonance is close to that by magnetometry measurements. For the wedged-Py/FeMn bilayers, the in-plane isotropic resonance field shift is positive and inversely proportional to the ferromagnetic layer thickness. It is originated from either specific geometry of Py layer thickness or interfacial diffusion. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetostriction at room temperature under various conditions of compressive prestress and applied fields of Tb[sub y]Dy[sub 1-y](Fe[sub 1-x]T[sub x])[sub 2] (T=Al, Mn) twin-free single crystals was investigated. The substitution of Al or Mn for Fe lowers the magnetostriction under ordinary temperature and pressure, and decreases the saturation field, which enables these materials with potential benefits for applications. Moreover, Tb[sub 0.5]Dy[sub 0.5](Fe[sub 0.9]Mn[sub 0.1])[sub 2] shows negative magnetostriction at room temperature under zero prestress, due to the rotation of domains 109.5° away from [111]. Under appropriate compressive stress, a quite large magnetostriction of 2160 ppm with a saturation field of 900 Oe and high d[sub 33] of 4.8 ppm/Oe can be obtained. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The crystal structure of the high Tc superconducting phase in a Pb-doped Bi-Sr-Ca-Cu-O system (nominal composition Pb0.3Bi1.7Sr2Ca3Cu4OY) with a zero-resistance temperature of 107 K was determined with transmission electron microscopy. The investigation shows that the crystal structure, which is different from the Pb-free one, is monocline with dimensions a=0.532 nm, b=0.383 nm, c=3.71 nm, α=β=90° and γ=134.8°. A distinct change of wave vector of incommensurate modulation was also observed. [ABSTRACT FROM AUTHOR]

Spin configuration, magnetocrystalline anisotropy compensation, and magnetostriction of TbxDy1-x(Fe0.8Co0.2)2 (0.20 ≤ x ≤ 0.40) compounds have been investigated. Experimental evidence for the anisotropy compensation has been observed directly by performing x-ray diffraction on magnetic-field aligned powders and by evaluating the Mössbauer spectra. The easy magnetization direction (EMD) at room temperature rotates from the <100> (x ≤ 0.27) to the <111> axis (x ≥ 0.32), subjected to the anisotropy compensation between Tb3+ and Dy3+ ions. The strong grain-<111>-oriented pseudo-1-3 epoxy/composite has been fabricated by curing under a moderate magnetic field. A giant low-field magnetostriction, longitudinal λ|| and linear anisotropic λa (=λ|| - λ⊥) up to 550 and 760 ppm at 3 kOe, respectively, is obtained for Tb0.32Dy0.68(Fe0.8Co0.2)2 composite, which can be attributed to anisotropy compensation, a large magnetostriction coefficients λ111, EMD lying along <111> direction, the strong <111>-textured orientation, and the chain structure. The good magnetoelastic properties, besides only containing 27 vol. % alloy particles in the insulating epoxy, make it a promising candidate for magnetostriction applications. [ABSTRACT FROM AUTHOR]

Flux pinning and anomalous magnetization peak of heavily overdoped Bi[sub 2-x]Pb[sub x]Sr[sub 2]CaCu[sub 2-y]Cr[sub y]O[sub 8+δ] [Cr-doping (Bi, Pb)-2212] single crystals are investigated by means of magnetization measurements with the magnetic field parallel to the c axis. Compared with undoped Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+δ] (Bi-2212) and Pb-doping Bi[sub 2-x]Pb[sub x]Sr[sub 2]CaCu[sub 2]O[sub 8+δ] [(Bi, Pb)-2212] single crystals, the irreversibility line of Cr-doping (Bi, Pb)-2212 single crystals is pronouncedly shifted to high temperatures. The anomalous magnetization peak H[sub 2p] with maximum peak field near 8000 G is observed. The H[sub 2p] exhibits strong temperature dependence from 0.19 to 0.93T[sub c]. The temperature dependence of H[sub 2p] can be explained according to vortex decoupling theory. The improved flux pinning may originate from reduced anisotropy due to Pb doping and a sufficient number of effective pinning centers due to the random Cr substitution on the Cu site. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]