A. Kozłowski

Strong out-of-plane magnetic anisotropy of Fe adatoms on Bi2Te3

The electronic and magnetic properties of individual Fe atoms adsorbed on the surface of the topological insulator Bi2Te3(111) are investigated. Scanning tunneling microscopy and spectroscopy prove the existence of two distinct types of Fe species, while our first-principles calculations assign them to Fe adatoms in the hcp and fcc hollow sites. The combination of x-ray magnetic circular dichroism measurements and angular dependent magnetization curves reveals out-of-plane anisotropies for both species with anisotropy constants of K-fcc = (10 +/- 4) meV/atom and K-hcp = (8 +/- 4) meV/atom. These values are well in line with the results of calculations.

Powder neutron diffraction studies of Zn-doped magnetite

We report on systematic neutron powder diffraction measurements of the temperature dependence of the crystal structure for the (x < 0.036) series. Time-of-flight data were collected on the spallation source ISIS (RAL, UK) between 4.2 and 270 K for samples showing different orders of the Verwey transition. The change of transition order is accompanied by the clear difference in the characteristic low temperature rhombohedral distortion. Namely, this distortion is independent of the dopant concentration for samples undergoing a first order Verwey transition, while the distortion for samples showing second order transition is much smaller and gradually diminishes with increasing Zn content. This distinct behaviour is linked to a change of atomic ordering from a well defined configuration for the first order regime to a dynamically changed arrangement for highly doped magnetite. This points to a close connection between the order of the Verwey transition and crystal lattice properties.

Electrical transport and magnetization measurements of Fe3−zAlzO4, z < 0.06

Abstract Electrical resistivity and saturation magnetization measurements are reported for Al-doped magnetite single crystals at low doping levels. The dependence of the Verwey transition temperature on Al concentration was determined based on resistivity data. Results of the magnetic measurements are compared with reported cation distributions. The role of Fe 2+ cations at tetrahedral positions is discussed.

Magnetically induced structural reorientation in magnetite studied by nuclear magnetic resonance

Phenomenon related to low symmetry phase of magnetite Fe3O4 below the Verwey transition is the switching of magnetic easy axis by external magnetic field connected with a structural transition. Results of nuclear magnetic resonance (NMR) studies of axis switching are presented, preceded by careful characterization by magnetic measurements. We detect changes in the F57e NMR spectra that evidence the structural transition interrelated with the axis switching. We also observe the switching process in time and analyze the dynamics of the phenomenon. Phenomenological approach according to Kolmogorov–Johnson–Mehl–Avrami is employed to find a link between the experimental data from magnetization measurements and NMR, showing that the effect observed by these two methods has the same origin. Additionally, NMR identifies separately the unswitched and switched phase during the switching process.

Thermal diffusivity of Fe/sub 3-x/Zn/sub x/O/sub 4/ at the Verwey transition

Thermal diffusivity (D) measurements of Fe/sub 3-x/Zn/sub x/O/sub 4/ single crystals in the vicinity of the Verwey transition (T/sub V/) have been performed through a photopyroelectric setup. The main features of D are the following: a decrease with increasing Zn content x, a different temperature dependence above and below T/sub V/ for every sample, and a drastic reduction just at T/sub V/. These changes in the thermal diffusivity behavior have been explained in terms of different phonon scattering mechanisms.

Possible influence of electron — lattice interactions on the Verwey transition in magnetite

In the paper crystal lattice influence on the Verwey transition in magnetite related compounds is discussed based on the experimental activity of our group. Heat capacity studies indicate the distinct low temperature lattice properties of slightly doped magnetite from those with higher dopant concentration. Neutron scattering lattice examination and the elastic constants studies are then performed to further study this conjecture. Our main conclusion is that the Verwey transition in magnetite can not be understood and described without strong involvement of lattice dynamics.

Specific heat of low doped magnetite, Fe3−xTixO4 and Fe3−yZnyO4

Abstract Systematic studies of specific heat and entropy of the Verwey transition in Fe 3− x Ti x O 4 and Fe 3− y Zn y O 4 series are reported. The results of these investigations demonstrate that in Fe 3− x Ti x O 4 and Fe 3− y Zn y O 4 systems exists only one, well defined phase transition. Both the entropy of the transition and transition temperature decrease with departure from Fe 3 O 4 composition.

Synchrotron x-ray scattering study of charge-density-wave order in HgBa2CuO4+δ

We present a detailed synchrotron x-ray scattering study of the charge-density-wave (CDW) order in simple tetragonal HgBa

Magnetostriction of First and Second Order Magnetite Samples and its Relation to the Magnetic Easy Axis Switching

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Analysis of Cationic Impurity Impact on Hyperfine Interactions in Magnetite

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