J.P. Rebouillat

Structures magnetiques de TbFeO3

Resume TbFeO 3 de structure perovskite (groupe Pbnm) est etudie par diffraction neutronique, mesures magnetiques et effet Mossbauer. A 97°K les spins du fer sont ordonnes suivant le mode G x appartenant a la representation Γ 4 ; a 4, 2°K les spins du terbium sont ordonnes suivant les modes F x et C y (Γ 2 ), et ceux du fer suivant G z couples dans la meme representation Γ 2 ; a 1, 5°K on observe les modes A x et G y (Γ 8 ) pour le terbium et un mode G (probablemennt G x ϵΓ 4 ) decouple du terbium pour le fer. Les temperatures de Neel des trois structures magnetiques sont respectivement 681°K 8, 4°K et 3, 1°K.

Some Neutron‐Diffraction Investigations at the Nuclear Center of Grenoble

In orthorhombic CrRO3 (R=rare earth and Y), Cr spins are ordered in a G mode between TN 282°K for R=La, to 112°K for R=Lu. The rare‐earth ordering is coupled to the Cr‐spin ordering, with the exception of terbium. In the magnetoelectric compound Fe1.15Ga0.85O3, four sites are available for cations, one of these mainly occupied by Ga. Neutron‐diffraction and magnetic‐susceptibility measurements give evidence of a ferrimagnetic ordering. Tetragonal FeS shows no evidence for magnetic ordering by neutron diffraction and Mossbauer effect down to 1.7°K. The CrS‐MnS solid solution has NaCl type. First kind of facecentered magnetic ordering is observed.

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.

Interpretation of the Magnetic Properties of the Rare Earth Chromites and the Rare Earth Manganites

The magnetostatic properties of the rare earth chromites, RCrO3, and those of the rare earth manganites, RMnO3, have been studied between 1.6° and 1500°K, in fields up to 28 000 Oe. These compounds are antiferromagnetic; they present two Neel points.For the rare earth chromites, the first Neel point varies between 112°K for LuCrO3 and 282°K for LaCrO3; it corresponds to the ordering of the spins of the Cr3+ ions; below this transition temperature, a ferromagnetism is superimposed upon the antiferromagnetism. The second Neel point is situated in the neighborhood of the temperature of liquid helium; it corresponds to the ordering of the moments of the rare earth ions.These properties are interpreted in terms of a molecular‐field model. The lattice of the Cr3+ ions and that of the R3+ ions are decomposed into two identical sublattices. The Cr‐Cr exchange interaction is negative; it is dominant; it defines principally the first Neel point. The R‐R interaction is negative and weaker; it defines the second Neel...

Pressure dependence of the resistivity of several amorphous alloys

Abstract Measurements under hydrostatic pressure of the electrical resistance of a series of metglas alloys and one alloy of NiY have been made in the range 0–5 kbar and 77–300 K. In general the behaviour fits no general pattern, except that Metglas 2204 (BeTiZr) obeys a simple prediction of the Ziman model as found by Nagel for thermopower.

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.

Magnetic properties of sandwich films based on RCo amorphous alloys (R = rare-earth, Y or Zr)

Abstract The magnetic properties of sandwich films, consisting of a soft amorphous CoZr layer placed between two SmCo layers with different coercivities, have been studied. Magnetization reversal in the different layers occurs under different field values and domain walls are then created (or annihilated) at the interface, due to the exchange interactions existing between the Co layers. A peculiar magnetization state has been stabilized in which the magnetization in the two SmCo layers are of opposite directions and a domain wall divides the CoZr central layer into two regions. In this state the magnetization processes are almost completely reversible, in contrast to the irreversible process observed in a single CoZr layer. The magnetization reversal mechanisms in this type of systems have been studied in YCo/GdCo bilayer, using transverse Kerr effect measurements. Nucleation/propagation has been found to occur in all instances.

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.