The anomalous Hall effect is investigated experimentally and theoretically for ferromagnetic thin films of ${\mathrm{Mn}}_{5}{\mathrm{Ge}}_{3}$. We have separated the intrinsic and extrinsic contributions to the experimental anomalous Hall effect and calculated the intrinsic anomalous Hall conductivity from the Berry curvature of the Bloch states using first-principles methods. The intrinsic anomalous Hall conductivity depends linearly on the magnetization, which can be understood from the long-wavelength fluctuations of the spin orientation at finite temperatures. The quantitative agreement between theory and experiment is remarkably good, not only near 0 K but also at finite temperatures, up to about $\ensuremath{\sim}240\text{ }\text{ }\mathrm{K}$ ($0.8{T}_{C}$).

Linear magnetization dependence of the intrinsic anomalous Hall effect.

Ferromagnetic Mn5Ge3 thin films were grown on Ge(111) with solid-phase epitaxy. The epitaxial relationship between the alloy film and substrate is Mn5Ge3(001)//Ge(111) with [100]Mn5Ge3//[110]Ge. The alloy films exhibit metallic conductivity and strong ferromagnetism up to the Curie temperature, TC=296 K. These epitaxial alloy films are promising candidates for germanium-based spintronics.

Epitaxial ferromagnetic Mn5Ge3 on Ge(111)

This review presents the recent progress in computational materials design, experimental realization, and control methods of spinodal nanodecomposition under three- and two-dimensional crystal-growth conditions in spintronic materials, such as magnetically doped semiconductors. The computational description of nanodecomposition, performed by combining first-principles calculations with kinetic Monte Carlo simulations, is discussed together with extensive electron microscopy, synchrotron radiation, scanning probe, and ion beam methods that have been employed to visualize binodal and spinodal nanodecomposition (chemical phase separation) as well as nanoprecipitation (crystallographic phase separation) in a range of semiconductor compounds with a concentration of transition metal (TM) impurities beyond the solubility limit. The role of growth conditions, codoping by shallow impurities, kinetic barriers, and surface reactions in controlling the aggregation of magnetic cations is highlighted. According to theoretical simulations and experimental results the TM-rich regions appear in the form of either nanodots (the dairiseki phase) or nanocolumns (the konbu phase) buried in the host semiconductor. Particular attention is paid to Mn-doped group III arsenides and antimonides, TM-doped group III nitrides, Mn- and Fe-doped Ge, and Cr-doped group II chalcogenides, in which ferromagnetic features persisting up to above room temperature correlate with the presence of nanodecomposition and account for the application-relevant magneto-optical and magnetotransport properties of these compounds. Finally, it is pointed out that spinodal nanodecomposition can be viewed as a new class of bottom-up approach to nanofabrication.

Spinodal nanodecomposition in semiconductors doped with transition metals

We have characterized the structural and magnetic properties of low-temperature molecular-beam epitaxy grown Ge:Mn by means of high-resolution transmission electron microscopy (HR-TEM), energy dispersive x-ray spectroscopy, and superconducting quantum interference device (SQUID) magnetometry. We find a coherent incorporation of Mn5Ge3 clusters in an epitaxially grown Ge:Mn matrix, which shows the characteristics of a diluted magnetic semiconductor phase of Mn-doped Ge. The clusters are preferentially oriented with the hexagonal [0001] direction parallel to the [001] growth direction of the Ge:Mn matrix, as determined from both HR-TEM and SQUID measurements.

http://www-old.mpi-halle.mpg.de/mpi/publi/pdf/6628_06.pdf

Structural and magnetic properties of Mn5Ge3 clusters in a dilute magnetic germanium matrix

In the active search for potentially promising candidates for spintronic applications, we focus on the intermetallic ferromagnetic ${\mathrm{Mn}}_{5}{\mathrm{Ge}}_{3}$ compound and perform accurate first-principles full-potential linearized augmented plane wave calculations within density functional theory. Through a careful investigation of the bulk electronic and magnetic structure, our results for the total magnetization, atomic magnetic moments, metallic conducting character, and hyperfine fields are found to be in good agreement with experiments, and are elucidated in terms of a hybridization mechanism and exchange interaction. In order to assess the potential of this compound for spin-injection purposes, we calculate Fermi velocities and degree of spin polarization; our results predict a rather high spin-injection efficiency in the diffusive regime along the hexagonal $c$ axis. Magneto-optical properties, such as ${L}_{2,3}$ x-ray magnetic circular dichroism, are also reported and await comparison with experimental data.

https://arxiv.org/pdf/cond-mat/0409734.pdf

First-principles characterization of ferromagnetic Mn 5 Ge 3 for spintronic applications

The spatial distribution of magnetisation density in the intermetallic compound Mn5Ge3 has been determined from a polarised neutron diffraction single-crystal study at 4.2 K. The positional and thermal parameters of the structure were derived from an unpolarised neutron study at 60 K, which also served to characterise the extinction in the material. The observed magnetic structure factors were fitted by a multipole expansion based on free-atom form factors for each of the two crystallographically inequivalent manganese atoms in the unit cell. The magnetic moment of the Mn1 atom with site symmetry 32 is 1.96(3) mu B and that of Mn2 with site symmetry mm is 3.23(2) mu B. The radial form factor of the Mn1 atom is found to be significantly contracted relative to that of a free Mn2+ ion. Evidence is presented that Mn-Mn interactions are the major factor leading to the difference in the moments on the two sites.

https://iopscience.iop.org/article/10.1088/0953-8984/2/11/014/pdf

J B Forsyth

Papers

The spatial distribution of magnetisation density in Mn5Ge3