A. Liénard

Amorphous yttrium-iron alloys. II. Mossbauer spectra

For pt.I see ibid., vol.11, no.12, p.2727 (1981). Mossbauer data are presented for eight Y1-xFex alloys with 0.32<or=x<or=0.88 in the temperature range 1.5-300K. In some cases external magnetic fields of up to 140 kOe were applied. Iron in the x=0.32 sample has essentially no magnetic moment. Magnetism in zero field appears near x=0.4 and the fraction of non-magnetic iron corresponds to the fraction possessing seven or more yttrium neighbours. The iron moment increases with the number of iron neighbours beyond six. An ordered state with a random non-collinear structure is found for all compositions except x=0.32. Data in an applied field of 50 kOe are interpreted in terms of idealised asperomagnetic structures where the iron moments are oriented at random within a cone of half-angle psi . psi decreases with increasing x, but collinear saturation cannot be achieved in any laboratory field. The average hyperfine field of iron in Y0.29Fe0.71 varies as (Hhf(T))=(Hhf(0))-cTn below 40K where n=1.1+or-0.1. An explanation is suggested in terms of single atom excitations where iron atoms in environments barely suitable for the existence of a moment are excited to low-lying non-magnetic states.

Hydrogen in amorphous magnetic alloys

Iron‐rich Y1−xFex amorphous alloys have been charged electrolytically with hydrogen to an H:Y ratio of approximately 3. The alloys are originally asperomagnetic, with spin freezing temperatures below 110 K, but they become soft ferromagnets on hydrogenation with Curie temperatures in excess of 400 K. The iron moment in a–Y12Fe88 changes from 1.96 to 2.24 μB in the hydride and the isomer shift increases by 0.15 mm/s. However, it appears that the main effect of the hydrogen is to shift a broad, mostly ferromagnetic exchange distribution with some antiferromagnetic interactions to an overwhelmingly ferromagnetic one. This is attributed to dilation of the iron–iron nearest‐neighbour distances. By contrast, no significant effects on magnetic moment or exchange were detected on hydrogenating amorphous Fe40Ni38Mo4B18 (Metglas 2826 MB), but the in‐plane anisotropy was modified and the soft magnetic properties degraded.

Laser ablation deposition and magnetic characterization of metallic thin films based on rare earth and transition metals

Abstract Laser ablation deposition (LAD) is a very promising technique for the preparation of thin films and multilayers. Technical difficulties inherent in the method have been solved. In particular a velocity selector has been developed leading to almost complete elimination of the droplets ejected from the target. The magnetic properties of a series of model systems prepared by LAD have been studied. The anisotropy of 30AFe(110)/W(110)/Al 2 O 3 (112¯0) is discussed. Epitaxial bilayers of 5AGd(0001)/25AFe(110)/W(110) have been obtained; the Gd moments are antiparallel to the Fe moments. Thin films of Y 2 Co 17 (0001) have been successfully grown on W(110)/Al 2 O 3 (112¯0) and their magnetic properties have been characterized.

d magnetism in the amorphous Y‐Co, Y‐Ni, and Y‐Fe alloys

In this paper we describe the magnetic properties of Y‐M amorphous alloys (M = Fe, Co, Ni) in which only 3d magnetism is involved. When the properties are not strongly dependent on environment effects, they are similar to those observed in the corresponding crystalline alloys: (i) Y‐Co and Y‐Ni alloys exhibit ferromagnetism when the 3d moment is large; (ii) far from the critical concentration for the disappearance of magnetism, the decrease of the 3d moment with increasing Y‐concentration is similar in amorphous and crystalline alloys; (iii) near the critical concentration, very weak itinerant ferromagnetism may be observed in amorphous Y‐Ni alloys as well as in the crystalline ones. On the contrary, the properties which are dependent on environment effects are strongly affected by the amorphous state: the properties of metamagnetism of itinerant electrons, which are very important in crystalline Y‐Co alloys near the critical concentration, lead in the amorphous state to a persistence of a mean 3d moment ...

Photoelectrodeposition of patterned cobalt films on silicon substrates

Cobalt films have been electrodeposited directly onto p-type (1 0 0) silicon substrates. Since electrons were required for reduction of the cobalt in solution, deposition only occurred in the presence of illumination. Projection of an optical grating onto the substrate during deposition demonstrated direct patterning of the Co which could lead to novel methods of defining magnetic structures on semiconductor substrates.

Magnetic structures and properties of the amorphous alloys DyT3; T = Fe, Co, Ni

Abstract Dy carries a well-defined free ion moment in amorphous DyT3, T = Fe, Co, Ni whereas the Fe and Co moments are 20% greater than in the corresponding crystals; Ni has a very weak moment. The magnetic structures are dominated by the randomly directed local anisotropy of the rare earth, which distributes the Dy moments over all directions within a broad come.

Ground state moment reduction in an ultra-thin W(110)/Fe(110)/W(110) film

Abstract The room temperature moment in a three monolayer Fe(110) film with a W(110) film at each interface has been determined by means of polarised neutron reflectivity and was found to be 1.8 μ B . The ground state value was evaluated by measuring the thermal dependence of the magnetisation from 300 to 4.2 K and found to be 2.1 μ B per atom which is less than that of bulk Fe.

Co anisotropy in amorphous Y1-xCox films

Abstract Transverse biased initial susceptibility measurements have been performed in amorphous Y1-xCox films. In the framework of the random anisotropy model for amorphous magnetism, a local anisotropy constant for Co of the order 107 erg/cm3 may be inferred from the results. This agrees with the low symmetry of environments in the amorphous state.

Magnetic and transport properties of amorphous NiY and FeY

We report resistivity and magnetoresistivity measurements on several samples of NiY and FeY over the temperature range 1.1 to 350 K and in magnetic fields up to 50 kOe. Although both systems are amorphous their transport and magnetic behavior is in strong contrast. NiY is extremely soft magnetically exhibiting characteristics of a weak itinerant ferromagnet. Its resistivity exhibits a minimum near 10 K with a logT region at lower temperatures and a relatively large positive ∂ρ/∂T at higher temperatures. The onset of magnetic order is seen in the transport data as a sharp step in ∂τ/∂T around Tc. On the other hand, FeY is very hard magnetically and has a resistivity characterized by a negative ∂ρ/∂T at all temperatures. The magnetoresistivity is positive and no effect is observed at the magnetic ordering temperature.

Epitaxial growth and magnetic properties of RM5 thin films (R=rare earth, M=Ni,Co,Fe) prepared by laser ablation deposition (abstract)

Different experimental methods have been developed in recent years for the preparation of metallic thin films and multilayers in which the individual layers consist of a simple element. We are developing another method, laser ablation deposition, which permits the congruent evaporation and deposition of almost any target to be obtained and is thus well suited to the preparation of thin films of intermetallic compounds. A major obstacle in the development of this technique in the past has been the formation of droplets, expelled from the target which pollute the prepared films. This has been solved recently with the use of a velocity selector to eliminate the droplets. YNi5 thin films, of thicknesses between 50 and 200 A, have been found to grow epitaxially on sapphire substrate, with the [0001] and [1010] sapphire directions being parallel, respectively, to the [0001] and [1120] YNi5 directions. YCo5 thin films, with thicknesses between 20 and 200 A, have been subsequently grown on YNi5. Their magnetic ...