Magnetic and electrical properties of iron-rich Ce(Fe1-xAlx)2 intermetallics: some remarks

Experimental results on magnetic and electric properties of Ce(Fe_1-xAl_x)₂, x < 0.10 are qualitatively discussed on the basis of previous theoretical studies. These studies agree with the existence of a canted spin phase in a certain concentration region.     

Magnetic and magnetotransport properties in Co5Cu95 melt-spun alloys

Giant magnetoresistance (GMR) has been observed in Co₅Cu₉₅ alloys fabricated by melt-spinning. The highest MR change of 28.0% occurs for Co₅Cu₉₅ after annealing at 450°C for 30 min. Based on the super-paramagnetic assumption, the average size of Co particles embedded in Cu matrix, ranging from 3.0 to 6.0 nm, has been determined by simulating the magnetization curves at 295 K which is higher than the blocking temperatures for the samples. Comparison with phenomenological theory for GMR indicates that the interfacial spin-dependent scattering is the dominant scattering mechanism underlying GMR origin in granular systems. Additionally, for the samples in as-quenched state or annealed at temperatureT _A=350°C, the electron hybridization and super-paramagnetic behaviors of fine Co particles may be responsible for the low value of MR change.     

Ground state magnetic properties of ultrathin fcc Fe and Co films on Cu(001) surfaces

The oxidation characteristics of silicon implanted with a low dose of nitrogen (1–3×10¹⁵cm^–2) have been studied for dry oxidation conditions at 1020°C. The wafers were subjected to a pre-oxidation annealing. Complete inhibition of the oxide growth occurs in the initial stage of oxidation, while the oxidation rate for prolonged oxidation is identical to that for pure silicon. The oxidation resistance increases with the implantation dose. The resistance is attributed to the formation of a nitrogen-rich surface film during annealing. This layer, which consists of only a few monolayers, is presumably composed of oxynitride. The electrical characteristics of MOS capacitors formed on implanted wafers show that the interface state density is not significantly increased by the low-dose N implantation.     

Magnetic properties and magnetocaloric effect in RE55Co30Al10Si5 (RE = Er and Tm) amorphous ribbons

The magnetic and magnetocaloric effects (MCE) of the amorphous $RE_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ ($RE={\rm Er}$ and Tm) ribbons were systematically investigated in this paper. Compounds with $R ={\rm Er}$ and Tm undergo a second-order magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) around Curie temperature $T_{\rm C} \sim 9.3$ K and 3 K, respectively. For Er$_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ compound, an obvious magnetic hysteresis and thermal hysteresis were observed at low field below 6 K, possibly due to spin-glass behavior. Under the field change of 0 T-5 T, the maximum values of magnetic entropy change ($-\Delta S_{\rm M}^{\rm max}$) reach as high as 15.6 J/kg$\cdot$K and 15.7 J/kg$\cdot$K for Er$_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ and Tm$_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ compounds, corresponding refrigerant capacity (RC) values are estimated as 303 J/kg and 189 J/kg, respectively. The large MCE makes amorphous $RE_{55}$Co$_{30}$Al$_{10}$Si$_{5 }$ ($RE={\rm Er}$ and Tm) alloys become very attractive magnetic refrigeration materials in the low-temperature region.     

Magnetic and electric properties of (Fe,Co)/(Si,Ge) multilayers

We review selected results concerning the interlayer exchange coupling in Fe/Si _x Fe_1−x , Fe/Ge and Co/Si layered structures. Among the ferromagnet/semiconductor systems, Fe/Si structures are the most popular owing to their strong antiferromagnetic interlayer coupling. We show that such interaction depends not only on semiconducting sublayer thickness, but also on deposition techniques and on the chemical composition of the sublayer as well. In similar heterostructures e.g. Fe/Ge, antiferromagnetic coupling was observed only in ion-beam deposited trilayers at low temperatures. In contrast, in Fe/Ge multilayers deposited by sputtering, no such coupling was found. However, when the Ge is partially substituted by Si, antiferromagnetic interlayer coupling appears. For Co/Si multilayers, we observed a very weak exchange coupling and its oscillatory behavior. The growth of Co on Si occurs in an island growth mode. The evolution of magnetic loop shapes can be successfully explained by the interplay between interlayer coupling and anisotropy terms.     

Magnetic properties of the pseudo-binary Fe2(Nb1-xMnx)

The magnetic behavior of the pseudo-binary system Fe₂(Nb_1-xMn_x) is investigated by means of the experimental techniques of X-ray diffraction (XRD), Mössbauer Spectroscopy (MS) and magnetization studies. The XRD results indicate that, up to x=0.3, all samples are single phase with hcp structure. This corresponds to the solubility limit of manganese in this phase. Above x=0.3, all prepared samples present the coexistence of three phases, two with hcp structure and one fcc. The magnetization measurements at low temperatures indicate that the transition temperature increases with the addition of Mn atoms in the Fe₂Nb host (T_N=10 K) up to 58 K for x=0.1. The Mössbauer spectra were fitted with a quadrupole splitting distribution, which indicates that the average quadrupolar splitting increases slightly with the increase of the manganese concentration.     

Pressure dependence of the weak itinerant ferromagnetism of Y(Co1-xAlx)2

Abstract

Y(Co_1-xAl_x)₂ is a weak itinerant ferromagnet for 0.12 < x < 0.20 with a maximum Curie point of about 25 K near x = 0.15. The pressure dependence of the Curie point for samples with 0.14 < x < 0.18 was measured in the temperature and pressure range 5–25 K and 0–8 kbar using a liquid filled lock cell. It was found that T_c was linear in pressure and extrapolated to OK at P_c = 9 ± 1 kbar for all samples. The volume expansion from YCo₂ to x = 0.15 is equivalent to a chemical pressure of -40 kbar so ferromagnetism cannot occur at the lattice constant of YCo₂.     

Magnetic properties of Fe and Co nanoclusters embedded in the first Cu(100) surface layer

The magnetic anisotropy energies, as well as spin and orbital magnetic moments of the atoms involved in the simplest nanostructures formed due to the self-organization within the first Cu(100) surface layer, are calculated in the framework of the density functional theory. The critical role of the surface relaxation, which leads to the rotation of the easy magnetization axis in iron nanoclusters, is demonstrated in the calculations of magnetic anisotropy.     

High coercivity Nd2(Fe,Co)14C-type ribbons prepared by melt spinning

Melt-spun Nd₁₃Dy₂Fe_77−xCo_xC₆B₂ (x=0, 5, 10, 15, 20) ribbons with a high coercivity more than 2 T have been obtained. It was found that the ribbons quenched at the optimum wheel speed 15 m/s (as-spun ribbons) mainly consist of ferromagnetic 2 : 14 : 1 phase and paramagnetic NdC₂ phase, and the ribbons spun at 25 m/s and subsequently annealed at 973 K for 15 min (as-annealed ribbons) are primarily composed of the magnetic 2 : 14 : 1 and 2 : 17 phases. The magnetization process of as-spun ribbons controlled by a pinning of the domain wall is different from that of as-annealed ribbons determined by a nucleation of the reverse domain. This significant difference originates possibly from the existence of paramagnetic NdC₂ phase acting as a pinning center in as-spun ribbons. In the as-annealed ribbons, the substitution of Co for Fe leads to increase of remanence (μ₀M_r), maximum energy product ((BH)_max) from 0.67 T, 9.7 MGOe for x=0 to 0.84 T, 14.4 MGOe for x=10, respectively. A coercivity of 2.74 T is obtained for as-quenched Nd₁₃Dy₂Fe_77−xCo_xC₆B₂ (x=0) ribbons.     

纳米复合永磁Pr9Fe74Co12B5Snx(x=0,0.5)的磁化行为与磁黏滞性

用熔体快淬法制备了纳米复合永磁样品Pr9Fe74Co12B5与Pr9Fe74Co12B5Sn0.5,分析了样品的起始磁化、反磁化过程,测得样品的总磁化率、可逆磁化率以及样品的磁黏滞性.结果表明,两样品在室温下均表现为单一硬磁相磁化行为,在低温下表现为双相行为,且由于添加Sn后使晶粒均匀化从而导致样品低温下的双相行为更加明显.添加Sn后引起样品中软磁相含量和软磁相晶粒尺寸的增加,使磁化反转中可逆磁化部分增多,且使反磁化形核场降低.磁黏滞性研究表明,热激活体积与软磁相晶粒的大小有关.     

Magnetic properties of (111) Cu/Fe multilayers

The magnetic properties of (111) Cu/Fe multilayers grown on Cu underlayers of several thickness (2000-500-50 Å) on cleaved mica have been investigated by Mössbauer spectroscopy and SQUID magnetometry. The analysis of experimental results suggests that 2.5 monolayers of ψ-Fe interfaced with Cu evolves partially from paramagnetic to ferromagnetic states as the Cu underlayer thickness is reduced to 50 Å and partially from weak to strong antiferromagnetism.     

Magnetic properties and microstructure of melt-spun Sm(Co,Fe,Cu,Zr)8 magnets

We report on the microstructural and magnetic properties of rapidly quenched Sm(Co_balFe_0.1Cu_xZr_0.04)₈ ribbons. Samples spun at velocities above 40 m/s are nanocrystalline and magnetically hard, even in the as-spun state. The coercivity and its temperature coefficient can be improved by annealing at 750°C. Samples spun at low speeds have low coercivity in the as-spun state and are characterized by larger grain sizes. By annealing a cellular precipitation structure within the grains, similar to that of bulk Sm(Co,Fe,Cu,Zr)_z magnets, can be obtained in Cu-containing samples, resulting in an increase of the coercivity, since the precipitates act as pinning centers. Some precipitation occurs even in as-spun Cu-free samples, indicating that their formation is not directly related to the existence of Cu, in contrast to the cellular structure. Compared to the bulk materials, lower annealing temperatures and shorter heat treatment times are required and the slow cooling process is not needed. The activation volumes for the magnetic reversal process are estimated by magnetic relaxation measurements.     

Surface vs. bulk magnetic properties of Co/Fe(0 0 1) and Fe/Co/Fe(0 0 1) as probed by linear magnetic dichroism in photoemission

The atomic-like behavior of the photoionization cross-section of core levels in solids is remarkably displayed in the observation of linear magnetic dichroism in the angular distribution (LMDAD) of photoelectrons. Nevertheless, structure-related effects are clearly visible as modulations of the dichroism signal, induced by photoelectron diffraction (PED). In this paper a comparison between the PED and LMDAD behaviours is presented for Fe 3p in Fe(0 0 1). In order to separate experimentally the surface and bulk contributions, ultrathin Co/Fe pseudomorphic overlayers were grown on the Fe(0 0 1) surface. Results confirms the PED nature of LMDAD modulations, which can be used as an estimate of the bulk sensitivity of the experiment.     

Epitaxial growth of fcc Fe on Cu(100)

Layer-by-layer epitaxial growth of Fe on Cu(100) is reported. The epitaxy is characterized using Auger electron spectroscopy and low energy electron diffraction intensity analysis. Good quality epitaxial Fe films having thicknesses ranging from one to four monolayers are stabilized by the Cu(100) substrate. The overlayer structure is shown to be nearly identical to a continuation of the fcc lattice of the substrate.