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In composite magnets, an in-depth understanding of magnetization reversal behaviors promotes optimizing the structure design of a magnet and improving its performance. In this work, the perpendicular magnetic anisotropic Ta/La–Pr–Fe–B/Dy/La–Pr–Fe–B/Ta multilayers have been prepared by adjusting the thickness of the Dy layer. The domain reversal evolutionary procedure has been investigated in different aspects including the characterization of domain morphology, micromagnetic analysis, and irreversible reversal distribution. It is confirmed that the nucleation mechanism is dominant in determining the coercivity of the multilayers with Dy diffusion. Dy diffusion helps to enhance the coercivity of the multilayers. The formation of Dy-containing hard magnetic phases and rare-earth-rich grain boundary phases by adding the Dy element leads to a strong nucleation field and isolation of hard magnetic phase grains, respectively. Our results aid in the understanding of magnetization reversal behaviors and enhance the magnetic properties of highly abundant rare-earth permanent magnetic multilayer films with the doping element. [ABSTRACT FROM AUTHOR]

Although the existence of liquid-liquid phase transition has become more and more convincing, whether it will terminate at a critical point and what is the order parameter are still open. To explore these questions, we revisit the fluid-liquid phase transition (FLPT) in phosphorus (P) and study its phase behavior by performing extensive first-principles molecular dynamics simulations. The FLPT observed in experiments is well reproduced, and a fluid-liquid critical point (FLCP) at T = 3000 ∼ 3500 K, P = 1.5-2.0 Kbar is found.With decreasing temperature from the FLCP along the transition line, the density difference (▵ p) between two coexisting phases first increases from zero and then anomalously decreases; however, the entropy difference (▵ S) continuously increases from zero. These features suggest that an order parameter containing contributions from both the density and the entropy is needed to describe the FLPT in P and at least at low temperatures, the entropy, instead of the density, governs the FLPT. [ABSTRACT FROM AUTHOR]

Gd nanoparticles and carbon coated Gd/GdC2 nanocapsules have been prepared by means of arc discharge in argon and methane, respectively. The possibility of the existence of the spin-glass-like state is discussed for Gd(O) nanoparticles and Gd(C) nanocapsules.

Bilayers consisting of La0.67Ca0.33MnO3 (LCMO) and SrMnO3 (SMO) have been prepared by pulsed-laser deposition on SrTiO3 (001) substrates. Unconventional magnetic coupling was found after cooling in a small field. The LCMO/SMO bilayers exhibit an exchange bias field of 209 Oe, which vanishes as the temperature rises above 90 K. A small magnetization has been found above the Curie temperature of the pure LCMO thin films. Spin-cluster-like antiferromagnetic (AFM)/ferromagnetic (FM) clusters have been deduced to exist at the interface due to the competing types of magnetic order at the interface. The magnetic relaxation is found to follow a doubleexponential equation and a slow relaxation process is observed due to the strong exchange coupling between AFM/FM clusters and the LCMO layer. We speculate that the short-range high-temperature FM order of the Mn3+ and Mn4+ moments above the Curie temperature at the interface gives rise to the magnetic regions that pin the FM LCMO layer as the temperature decreases. [ABSTRACT FROM AUTHOR]

Bilayers of La0.7Sr0.3MnO3/NiO and LaMnO3/NiO were prepared and magnetic exchange coupling investigated in these bilayers, where the Curie temperature of the ferromagnetic (FM) layer is lower than the Néel temperature of the antiferromagnetic layer. After small-field cooling, the LSMO/NiO bilayer exhibits an exchange bias with field HEB = 60 Oe, whereas the LMO/NiO sample shows weak magnetic interaction (∼22 Oe). The unconventional exchange bias in LSMO/NiO bilayer vanishes as temperature rises above 50 K. The weak magnetic interaction at the LMO/NiO interface is due to a larger Hubbard parameter value and smaller transfer integral value in the Mott insulator LMO compared with that for the FM conductor LSMO. The valence states of Mn and Ni ions across the interfaces for LSMO/NiO and LMO/NiO have been studied using X-ray photoelectron spectroscopy. We speculate that the FM interaction between Ni2+ and Mn4+ gives rise to magnetic regions that pin the ferromagnetic LSMO layer. [ABSTRACT FROM AUTHOR]

NiO/ZnO nanocomposites with NiO content of 4 at. % and 20 at. % were annealed up to 1200 °C to get Ni doped ZnO nanocrystals. Raman scattering spectra illustrate a broad and strong band at 500-600cm-1 in all nanocomposites after annealing above 700 °C, which suggests incorporation of Ni in the ZnO lattice. However, x-ray diffraction measurements show that NiO phase can be still observed in all nanocomposites after annealing, which indicates that Ni is partially doped into the ZnO structure. Positron annihilation measurements reveal large number of vacancy defects in the interface region of all nanocomposites, and they are gradually recovered with increasing annealing temperature up to 1000 °C. Room temperature ferromagnetism can be observed in the NiO/ZnO nanocomposites, which is stronger in the 20 at. % NiO/ZnO nanocomposites, and the magnetization decreases continuously with increasing annealing temperature. This indicates that the ferromagnetism at low annealing temperatures originates from the NiO nanograins, and they become antiferromanetic after subsequent higher temperature annealing which leads to the weakening of ferromagnetism. After annealing up to 1000 °C, the ferromagnetism in both the two samples becomes nearly invisible. The disappearance of ferromagnetism shows good coincidence with the recovery of vacancy defects in NiO/ZnO nanocomposites. It can be inferred that the ferromagnetism is mediated by vacancy defects which are distributed in the interface region. [ABSTRACT FROM AUTHOR]

OBJECTIVE: Bone marrow mesenchymal stem cells (BMSCs) promote bone tissue repair. MiR-1 regulates myogenic and osteogenic differentiation of human adipose tissue stem cells. However, miR-1's effect on BMSCs osteogenesis is unclear. MATERIALS AND METHODS: Rat BMSCs were isolated and divided into control group, miR-1 group, and si-miR-1 group respectively transfected with miR-1 plasmid and miR-1 siRNA followed by analysis of cell proliferation by MTT assay and Caspase 3 activity. The expression of osteogenic genes Runx2 and OPN was measured by Real Time-PCR. Healthy male Sprague-Dawley rats were separated into fracture group, NC group, and si-miR-1 group followed by analysis of bone mineral density, miR- 1 level by Real Time-PCR, type I collagen, and BMP-2 by enzyme-linked immunosorbent assay (ELISA), and TLR1 expression by Western blot. RESULTS: Transfection of miR-1 siRNA into BMSCs significantly downregulated miR-1 expression, promoted BMSCs cell proliferation, inhibited Caspase 3 activity, as well as promoted osteogenic genes Runx2 and OPN expression and decreased TLR1 expression (p<0.05). The upregulation of miR-1 expression significantly reversed the above changes. TLR1 is a target of miR-1. Downregulation of miR-1 expression in BMSCs of fractured rats significantly increased bone density and ALP activity, promoted type I collagen and BMP-2 expression, and decreased TLR1 expression (p<0.05). CONCLUSIONS: The downregulation of miR-1 promotes BMSCs osteogenic differentiation via targeting TLR1, which promotes osteogenic differentiation and bone healing. [ABSTRACT FROM AUTHOR]

First-principles calculations were employed to study the magnetic properties of ZnO nanoclusters (NCs). It is demonstrated that the magnetism of the ZnO nanoclusters is dominated by the dangling-bond states of the surface oxygen ions surrounded by two Zn cations. Such surface-state driven magnetism can be completely destroyed by hydrogen passivation and thus is very sensitive to the chemical environments of the NCs. The theory indicates that magnetism may be steadily observed in appropriately encapsulated ZnO nanoparticles or around their grain boundaries, which is consistent with the previously reported experiments. [ABSTRACT FROM AUTHOR]

The effect of interstitial nitrogen on the phase transition and magnetocaloric behavior of MnAs1-xSixNδ (x=0.03, 0.06, and 0.09) is investigated. The interstitial nitrogen atoms cause the step-scanned x-ray diffraction peaks to shift toward lower angles and lower the Curie temperature, whereas silicon addition increases the Curie temperature to near room temperature. The thermal hysteresis is reduced to nearly 0 in 1-xSixNδ, which is beneficial to practical applications. For a field change of 5 T, the largest magnetic entropy change and refrigerant capacity are 14.6 J Kg-1 K-1 at 247 K and 360 J K-1, which is slightly higher than the entropy change in the parent alloy. Finally, we briefly discuss the occurrence and origin of the "virgin effect" in MnAs. [ABSTRACT FROM AUTHOR]

Magnetic properties and magnetocaloric effect of the ferrimagnetic compounds Gd4Co3 and (Gd0.9Dy0.1)4Co3 have been studied. In Gd4Co3, two successive magnetic-entropy changes occur due to a spin-reorientation transition at TSR=163 K and a ferrimagnetic-magnetic ordering transition at TC=220 K. For a field change from 0 to 5 T, -ΔSMmax at TC is 5.74 J/kg K, the full width at half maximum (δTFWHM) of the -ΔSM versus T curve has a high value of 131 K, and the refrigerant capacity is as high as 575 J/kg. TC can easily be tuned by Dy substitution for Gd and the magnetic-entropy change is increased simultaneously. -ΔSMmax of (Gd0.9Dy0.1)4Co3 at TC=145 K for the same field change has increased to 8.47 J/kg K. Our studies suggest that the successive magnetic transitions could enlarge the temperature interval, which makes this type of material meaningful for magnetic refrigeration in wider temperature regions than conventional materials. [ABSTRACT FROM AUTHOR]

Exchange coupling has been realized in textured Nd2Fe14B/α-Fe multilayer films. A Mo spacer layer has proved to be effective for preventing interdiffusion at the interface region between the hard-magnetic Nd16Fe71B13 and the soft-magnetic α-Fe layer in these multilayer films. Anisotropic behavior of the exchange coupling in the films is observed by means of magnetic measurements. Furthermore, the effective critical correlation length is found to exhibit anisotropic behavior, which is smaller in the parallel than in the perpendicular direction at the same temperature. This anisotropic behavior of the multilayer films can be well explained by taking into account the shape anisotropy of the textured grains. [ABSTRACT FROM AUTHOR]

The structure, phase components, and magnetic properties of antiferromagnetic coupled Fe2O3 and NiO nanocomposites have been investigated. A negative exchange bias field of about 2 kOe and the anomalous shape of hysteresis loop are observed, which may be related to uncompensated and pinned antiferromagnetic spins at the interface between ferrimagnetic and antiferromagnetic phases in the powders. Furthermore, the exchange bias field varies with the strength of cooling field, and the exchange bias field HE of 0.76 kOe is observed in antiferromagnetic-antiferromagnetic system. [ABSTRACT FROM AUTHOR]

Structure and magnetic properties of mechanically alloyed Cu-doped SmCo6.7-xCuxCr0.3 (x=0.1–0.7) magnets have been systematically studied. The magnetically hard main phase is found to be of Th2Ni17 type in the SmCo6.7-xCuxCr0.3 alloys. A small amount of Cu addition is favorable for the formation of the 2:17 phase/Co nanocomposite structure in the alloys. The increase of Cu doping results in more Cu precipitating in the alloys with separating the grains, which significantly enhances the intrinsic coercivity iHc of the alloys and weakens the exchange coupling between the magnetically hard and soft phases. The magnetization reversal processes of the magnets have been discussed, upon the measurement of the recoil curves. [ABSTRACT FROM AUTHOR]

The spin configuration and magnetostrictive properties of TbxDy0.7-xPr0.3(Fe0.9B0.1)1.93 (0.10<=x<=0.28) Laves compounds are investigated. The spin phase diagram for the compounds is constructed to illustrate both the composition dependence of the Curie point TC and spin reorientation temperature TSR and the arrangement for the easy magnetization direction (EMD). It is found that when x is increased from 0.16 to 0.28, TC increases from 617 to 623 K, while TSR decreases from 375 to 160 K at which the EMD reorients from <100> to <111> axis. The magnetization and magnetostriction of the compounds are measured as a function of applied field. The magnetocrystalline anisotropy constant K1 and the ratio λa/K1 reach a minimum and a maximum value at x=0.22, respectively. The single phase Tb0.22Dy0.48Pr0.3(Fe0.9B0.1)1.93 compound has the lowest magnetocrystalline anisotropy, the highest magnetostriction to anisotropy ratio, and a large spontaneous magnetostriction λ111 of ∼1500 ppm at room temperature. In view of these properties, the compound is a promising magnetostrictive material. [ABSTRACT FROM AUTHOR]

SmCo7-xCrx (x=0–0.6) magnets have been synthesized by mechanical alloying and subsequent annealing. A small amount of Cr favors the formation of Th2Ni17-type 2:17 phase and increasing the Cr content can extend the temperature range in which the hexagonal 2:17 phase remains stable. The coercivities of the SmCo7-xCrx magnets are significantly enhanced by increasing the Cr content. The highest coercivity of 15.8 kOe is obtained for the SmCo6.4Cr0.6 alloy annealed at 700 °C for 30 min. The transformation of Th2Ni17-type structure to Th2Zn17-type structure is observed when increasing the annealing temperature. The magnetization reversal process of the alloys has been discussed, according to the measurement of initial magnetization curves and minor hysteresis loops. [ABSTRACT FROM AUTHOR]

Gd nanoparticles and carbon coated Gd/GdC[sub 2] nanocapsules have been prepared by means of arc discharge in argon and methane, respectively. In the Gd nanoparticles, gadolinium oxide was detected by x-ray diffraction, while the presence of metallic gadolinium was proved by oxygen analysis and x-ray photoelectron spectra. In the nanocapsules, the existence of GdC[sub 2] and Gd was detected by x-ray diffraction. Shell/core structures were observed for either the nanoparticles (with diameters larger than 20 nm) or the nanocapsules. The magnetization data above 25 K, when scaled as a function of μ[sub 0]H/T, fall on a universal curve while the deviation of the magnetization curves at 4.2 K from the universal curves was ascribed to the superparamagnetism–ferromagnetism transition of small Gd particles. The temperature dependence of magnetization supports the theoretical predictions for very tiny Gd nanoparticles. The presence of metallic Gd in these nanocapsules results in comparatively high magnetization of about 60.5 A m2/kg at 4.2 K, compared with the carbon-coated gadolinium carbide nanocapsules without the metallic Gd core. The possibility of the existence of the spin-glass-like state is discussed for Gd(O) nanoparticles and Gd(C) nanocapsules. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetic properties and exchange couplings of nanocomposite (Nd,Y)[SUB2]Fe[SUB14]B/α-Fe magnets prepared by mechanical milling have been investigated at low temperatures. With decreasing temperature, due to Y substitution for Nd, an extension of the exchange coupling length in nanocomposite magnets occurs in a wider temperature range. This can be attributed a decreasing anisotropy of the hard-magnetic phase so that more soft-magnetic grains participate the exchange coupling. Close to 135 K, due to the spin reorientation, the hard magnetic phase is not more uniaxail, which leads to a drastic decrease of the magnetic properties of the Nd[SUB2]Fe[SUB14]B-based nanocomposite magnets. [ABSTRACT FROM AUTHOR]

Studies the structural transformations from amorphous metastable-to-equilibrium phases during annealing treatment of rapidly quenched Nd[sub 10]Fe[sub 90-x]Ti[sub x] alloys. Crystallization of the amorphous alloys below 700 degrees Celsius; Transformation of the CaCu[sub 5]-type structure into a TbCu[sub 7]-type structure.