A. Broddefalk

Structural and magnetic properties of (Fe1-xCox)3P compounds : experiment and theory

Abstract The structural and magnetic properties of (Fe1−xCox)3P compounds have been investigated by means of X-ray and neutron diffraction experiments, magnetization measurements and first-principles calculations. The saturation magnetization and the transition temperature of (Fe1−xCox)3P decrease with increasing Co concentration. The magnetic moments on the three non-equivalent metal sites are determined in detail by means of neutron diffraction experiments and first principles calculations which both show that the moments on the different sites have different magnitudes and they all decrease with increasing Co concentration. Results show that Co preferentially substitutes Fe on two of the metal sites. The complex behavior of the individual magnetic moments and the site preferences of Co substitution are discussed in terms of atomic radius, coordination numbers, and eigenvalue sums.

A study of the structural and magnetic properties of TlCo2−xCuxSe2

Abstract The structural and magnetic properties of TlCo 2− x Cu x Se 2 have been investigated experimentally. The antiferromagnetic coupling already found in TlCo 2 Se 2 prevails on copper substitution but is weakened. For high copper contents, x >1.3, Pauli paramagnetism occurs. The susceptibility measurements point towards a picture of ferromagnetic Co moments aligned perpendicular to the c -axis. The cobalt atoms are confined to sheets, between which there is antiferromagnetic coupling. Structurally we observe a change in symmetry from I-centred tetragonal ( Z =2) to face-centred orthorhombic ( Z =4) in the range 0 x 2 Se 2 has been re-investigated by neutron powder diffraction. Below T N ∼80 K, it is characterised by a helimagnetic arrangement of spins confined to the Co sheets, the helix running along the c -axis. The moments lie in the (002) planes with a helical turn angle of about 121° between two adjacent Co layers. At 10 K, the moment refined to 0.46 μ B /Co atom.

Structural and magnetic properties of bcc Fe/Co (001) superlattices.

In thin layered Fe/Co (0 0 1), grown on MgO (0 0 1), both Fe and Co crystallize in the body-centered cubic (BCC) structure, as seen in a series of superlattices where the layer thickness of the components is varied from two to twelve atomic monolayers. These superlattices have novel magnetic properties as observed by magnetization and polarized neutron reflectivity measurements. There is a significant enhancement of the magnetic moments of both Fe and Co at the interfaces. Furthermore, the easy axis of the system changes from [1 0 0] for films of low cobalt content to [1 1 0] for a Co content exceeding 33%. No indication of a uniaxial anisotropy component is found in any of the samples. The first anisotropy constant (K1) of BCC Co is found to be negative with an estimated magnitude of 110 kJ/m3 at 10 K. In all cases, the magnetic moments of Fe and Co have parallel alignment.

In-plane magnetic anisotropy of Fe/V (0 0 1) superlattices

Abstract The magnetization and the in-plane magnetic anisotropy energy of Fe (15 ML )/ V (1 – 12 ML ) superlattices have been examined and their relation to the growth of the superlattices is discussed. The individual lattice parameters of the strained Fe and V layers are calculated theoretically from the elastic energy. The calculations rather accurately reproduce the experimentally derived average lattice parameters of the superlattices. The measured in-plane magnetic anisotropy is compared to calculated results employing bulk values of the anisotropy constants and magnetoelastic coupling coefficients. A good agreement between the results is found provided interface coefficients are included in the calculations. A first principles study reproduces an observed reduction in saturation moments of the interface and is shown to be caused by an induced moment on the interface V atoms that couple antiparallel to the Fe moments in combination with a reduction of the magnetic moments of the Fe atoms at the interface. A theoretical calculation of bulk Fe reproduces the experimental ‘bulk’ contribution to the magnetocrystalline anisotropy and the magnetoelastic coupling of the films.

The antiferromagnetism of (Fe1−xMnx)3P, x⩾0.67, compounds

Abstract The structural and magnetic properties of (Fe 1− x Mn x ) 3 P compounds, in the concentration range 0.67⩽ x ⩽1, have been investigated by means of X-ray and neutron diffraction experiments, magnetisation measurements, Mossbauer spectroscopy and first principles electronic structure calculations. The magnetic ordering temperatures obtained from the different techniques were consistent with each other but different from previously published results. The magnetisation curves and neutron diffraction intensities can be explained by an antiferromagnetic ordering with a magnetic unit cell four times larger than the crystallographic unit cell. The magnetic moments are small as judged from neutron diffraction and Mossbauer spectroscopy results. The band calculations on the other hand suggest a competition between Pauli paramagnetism and magnetic solutions with large magnetic moments.

Structural and magnetic properties of TlCo2−xCuxSe2, 0⩽x⩽1

Abstract Structural and magnetic properties of single-crystal TlCo 2−x Cu x Se 2 , 0⩽x⩽1 , have been investigated by means of X-ray diffraction experiments and magnetisation measurements. TlCo2Se2 and TlCu2Se2 are isostructural, belonging to the ThCr2Si2 structure type, i.e. tetragonal sheet structures. From diffraction data on the solid solutions, we note superstructure formation at large Cu concentrations. The overall ordering at low temperature is antiferromagnetic, and the Neel temperatures scale linearly with x, falling drastically from 82 K (x=0) to 11 K (x=1). From fits to the Curie–Weiss law, the effective magnetic moments μeff and the asymptotic Curie temperatures θp were obtained. θp is positive, showing that the interactions within the sheets are of a ferromagnetic character.

Study of Amorphous Ferrimagnet Fe0.66Er0.19B0.15 by Means of Monochromatic Circularly Polarised Source

Properties of amorphous alloy Fe0.66Er0.19B0.15 are reported. A reorientation of the Fe and Er magnetic moments during sample cooling through the compensation point in a large magnetic field is found by means of monochromatic circularly polarised radiation.