Magnetic properties of Fe/ZnSe/Fe trilayers

The magnetic properties of Fe/Zn/Fe trilayers have been studied by ferromagnetic resonance and magnetization measurements. These measurements have been used to investigate the magnetic anisotropy of the iron layers and the magnetic coupling across the semiconductor spacer. The angular dependence of the resonance spectra has been measured in-plane and out-of-plane in order to deduce magnetic anisotropy constants of the samples. Experimental data were fitted by using an energy-density expression that includes bulk cubic anisotropy, growth-induced uniaxial in-plane anisotropy and perpendicular-surface anisotropy terms. A small ferromagnetic coupling is observed in the trilayers with spacer thickness up to .     

Magnetic and magnetoresistive properties of epitaxial Co/Cu/Co trilayers on Si(111)

Giant magnetoresistance of the epitaxial Co/Cu/Co trilayers grown on vicinal Si(111) was determined as a function of Cu spacer coverage in the range from 0 to 7 ML. The first maximum of giant magnetoresistance and antiferromagnetic coupling was detected at 3.0 ML coverage of the Cu spacer. The portion of antiferromagnetic coupling in the first antiferromagnetic maximum was estimated as 17%. 3D growth mode of the Cu spacer leads to the simultaneous occurrence of the ferromagnetically and antiferromagnetically coupled areas between the Co layers.     

Role of the external surfaces on the superconducting properties of superconductor/normal metal trilayers

Superconducting proximity effect is studied in superconductor/normal metal trilayers. The dependences of the superconducting transition temperature _Tc$T_c$ versus Nb thickness in Cu/Nb/Cu systems and versus Cu thickness in Nb/Cu/Nb ones are described by different values of the microscopical parameters. We attribute this difference to the influence of the external surfaces of the Nb/Cu/Nb hybrids on the superconducting properties of the system.     

Microscopic theory of equilibrium properties of F/S/F trilayers with weak ferromagnets

The aim of this paper is to explain the non monotonic temperature dependence of the self-consistent superconducting gap of ferromagnet/superconductor/ferromagnet (F/S/F) trilayers with weak ferromagnets in the parallel alignment (equivalent to F/S bilayers). We show that this is due to Andreev bound states that compete with the formation of a minigap. Using a recursive algorithm we discuss in detail the roles of various parameters (thicknesses of the superconductor and ferromagnets, relative spin orientation of the ferromagnets, exchange field, temperature, disorder, interface transparencies).Received: 23 January 2004, Published online: 29 June 2004PACS: 74.78.Na Mesoscopic and nanoscale systems - 74.45. + c Proximity effects; Andreev effect; SN and SNS junctions - 74.50. + r Tunneling phenomena; point contacts, weak links, Josephson effects     

Triplet proximity effect in FSF trilayers

We study the critical temperature T _c of FSF trilayers (F is a ferromagnet, S is a singlet superconductor), where the triplet superconducting component is generated at noncollinear magnetizations of the F layers. An exact numerical method is employed to calculate T _c as a function of the trilayer parameters, in particular, mutual orientation of magnetizations. Analytically, we consider limiting cases. Our results determine the conditions necessary for the existence of recently investigated odd triplet superconductivity in SF multilayers.     

Magnetic properties of ferrihydrite

The magnetic properties of a sample of synthetic ferrihydrite have been investigated by use of Mössbauer spectroscopy. The area ratios of the Mössbauer lines are not significantly changed by application of magnetic fields at 5 K, indicating an amorphous magnetic structure. An average magnetic moment per particle of 3.1×10^?21 JT^?1 was estimated from the dependence of the hyperfine splitting of the Mössbauer spectra on external magnetic fields at 80 K.     

Magnetic properties of GdMg

The lattice constants at room temperature and the magnetic properties of several members of the series Gd_χLa_1-χMg were studied in the temperature range 4.2–300 K with applied fields up to 340 kG. Several of the pseudo-binary compounds were found to give rise to antiferromagnetic ordering in low applied fields. In their magnetic isotherms at 4.2 K critical fields occur which are associated with the destruction of the antiferromagnetic ground state. These critical fields were found to increase with La concentration. It is shown that in Gd_χLa_1-χMg the antiferromagnetic interaction between the Gd spins decreases with increasing χ whereas the ferromagnetic interaction increases in the same sense. In GdMg the antiferromagnetic interaction has almost completely vanished, so that superficially this compound looks like a normal ferromagnet.     

磁性多层薄膜中交换各向异性研究

采用铁磁共振理论研究了自旋阀体系中交换各向异性场和两铁磁薄膜厚度对体系性质的影响,得到系统色散关系的解析表达式.研究表明:体系中存在的交换各向异性场H_E对声学模和光学模的共振场均有影响(其对声学模的影响较大).而且还发现声学模共振场随A,B层铁磁薄膜厚度的变化关系依赖于系统中交换各项异性场的强弱;相反,光学模共振场随两铁磁层厚度的增加始终增强.     

Magnetic properties of carbonado diamonds

Carbonados are porous polycrystalline diamonds of uncertain origin, which are found at locations in Bahia (NE Brazil) and in the Central African Republic. Their combination of extreme hardness and toughness is ideal for drilling and cutting tools. A variety of elements including Fe, Ni, Cu and Ag are associated with the diamonds. Following a suggestion that Mn-doped diamond may be intrinsically ferromagnetic, we have analysed six samples from Brazil which show ferromagnetic moments of up to 3 A m² kg⁻¹, which is reduced by acid leaching. X-ray diffraction on the crushed powder showed a cubic diamond structure, with no secondary phases visible. Scanning electron microscopy shows an inhomogeneous distribution of heavy metals and Mössbauer spectroscopy indicates that iron is present as native iron. We find no evidence from the carbonados for the existence of transition-metal doped ferromagnetic carbon. The intrinsic diamagnetic susceptibility of carbonados is −4.5×10⁻⁹ m³ kg⁻¹, similar to the accepted value for diamond,−5×10⁻⁹ m³ kg⁻¹.     

Magnetic properties of uranium hexacyanomanganate

A Prussian blue type compound of the stoichiometric composition U^IV[Mn^II(CN)₆]·5H₂O has been prepared. It has been shown that the compound exhibits ferrimagnetism with a Curie temperature T_c=36.8 K.     

Magnetic properties of Co-impregnated zeolites

The structure and magnetic properties of Co-containing zeolites prepared by wet impregnation were investigated. The samples were calcined and then reduced in flowing H₂. The samples studied have large saturation magnetization due to the presence of cubic Co particles over a wide range of sizes. The zero field cooling-field cooling curves show a sharp magnetization peak with a blocking temperature around 7 K followed by an exponential decay and two other peaks—of much lower amplitude—around 160 and 280 K. The low temperature peak is analyzed considering first, at T_crit, thermal relaxation toward equilibrium over an energy barrier, with increasing viscosity S with T. Above T_crit relaxation does not occur and viscosity abruptly goes to zero. The behavior of the smallest Co particles is unusual above the blocking temperature.     

Magnetic properties of Cr-Fe-Mn alloys

The magnetic behaviour of a Cr_80−xFe₂₀Mn_x alloy system with x=2, 7, 10, 13 and 22 has been investigated in the temperature range 2-400 K through measurements of magnetization, electrical resistivity, magnetoresistivity, specific heat and thermal expansion. The temperature vs. Mn concentration magnetic phase diagram of the system is rich in magnetic behaviour with ferromagnetic (FM), antiferromagnetic (AFM) and paramagnetic phase regions and a spin-glass (SG) region at the lowest temperatures. Phase transition temperatures amongst these different magnetic phases could be identified from well-defined anomalies of magnetic origin that are displayed by graphs of the above-mentioned physical properties as a function of temperature. The time relaxation of the thermoremanent, isothermal remanent and field-cooled magnetizations below and above the SG freezing temperature show unusual aspects. These relaxations do not follow the usual superposition principle that is expected for typical SG materials. Negative giant magetoresistance (GMR) is observed in the alloys at 4 K. The GMR initially increases sharply on increasing the Mn content in the alloy system, followed by a tendency towards a saturation negative value for concentrations of more than about 10 at% Mn. Low-temperature plots of C_p/T vs. T², where C_p is the specific heat, present anomalous behaviour for alloys with x=2, 10 and 22. For x=2 the plot shows an upturn at the lowest temperatures that changes over to a prominent downturn for x=10 and 22. This behaviour is attributed to Fe concentration fluctuations in the alloys, confirming the theoretical model of Matthews.     

Magnetic properties of maghemite nanoparticles

Magnetic particles of maghemite (spinel γ-Fe₂O₃) are synthesized by means of aerosol pyrolysis, making it possible to produce chemically uniform highly-dispersed single-phase materials. The magnetic properties of synthesized particles for temperatures ranging from helium temperature up to room temperature and higher are investigated using a SQUID magnetometer. The experimental curves are compared to the results from calculations performed by the Monte Carlo method. It is found that the Curie temperature is lower for γ-Fe₂O₃ nanoparticles than for bulk samples. Several parameters of the material are estimated by comparing the experimental and calculated results.     

Magnetic properties of ternary compounds

Summary At present magnetism is becoming a more and more fundamental science. On the other hand, the solid-state chemists are able to prepare easily many new ?magnetic? phases with a more or less complex crystal structure. There results a conflicting situation between the ideal expected models and the true behaviour of the real crystal. A strategy to tackle this important problem is suggested. Illustrations are given by analysing the properties of ternary compounds with different structural arrangements of their magnetic carriers such as chains or layers. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Magnetic properties of CuRh alloys

By means of rapid quenching techniques single phased samples of Cu_xRh_1?x(0?x?1) were obtained. For these alloys the Knight shift of ⁶³Cu and ¹⁰³Rh has been determined employing pulsed NMR at low temperatures, furthermore the magnetic susceptibility was measured for temperatures between 4.2 and 300 K. While the Knight shift of ¹⁰³Rh is dominated by s-electron contributions in spite of a high density of d-states at the Fermi level, for the susceptibility, however, the d-electron contributions prevail. In addition the susceptibility shows a pronounced maximum at about 10 at.% Cu. Using the extrapolated Knight shift of copper (x→0) we estimate a net copper hyperfine field of — 15 T in close agreement with the corresponding values for CuPd and CuPt.