Mn5Ge3 Thin Films Research Articles

Epitaxial growth and magnetic properties of Mn5(SixGe1-x)3 thin films

Structural and magnetic properties of Mn5(SixGe1-x)3 thin films were investigated. Ferromagnetic Mn5Ge3 and anti-ferromagnetic Mn5Si3 thin films have been synthesized and characterized as these compounds exhibit interesting features for the development of spintronics. Here, Mn5(SixGe1-x)3 thin films were grown on Ge(111) substrates by co-deposition using molecular beam epitaxy. Crystalline thin films can be produced with controlled Si concentrations ranging from 0 to 1. The thin films were relaxed by dislocations at the interface with the substrate. A lattice parameter variation was observed as the Si content increased, which is comparable to previous works done in bulk. Reflection high-energy electron diffraction diagrams and X-ray diffraction profiles showed that lattice parameters a and c are shrinking and that the surface roughness and crystallinity degrade as the Si amount increases. Magnetometric measurements revealed a ferromagnetic behavior for all Si concentrations. The measured average ferromagnetic moment per manganese atom decreased from 2.33 to 0.05 μB/Mn atom. No ferro to anti-ferromagnetic transition was observed contrary to the bulk Mn5(SixGe1-x)3 compound.

The influence of substrate orientation on the magnetic behavior of nearly-stoichiometric Mn5Ge3 thin films: DFT calculations and experimental analysis

The Mn5Ge3 exhibits a wide range of fascinating properties such as high spin polarization up to 42 %, large spin diffusion lengths, near-room Curie temperature, and possible integration with Ge, GaAs, and Si substrates. The influence of substrate orientation on magnetic behavior has been investigated. The thin films studied present an in-plane magnetic reversal which is isotropic in samples grown on GaAs(111) and anisotropic in samples grown on GaAs(001). Another difference observed is a linear trend to saturation on the out-of-plane hysteresis loop in samples grown on GaAs(111), comparatively to samples grown on GaAs(001). To better understand this scenario, Density Functional Theory (DFT) calculations were conducted. The results indicate a ferromagnetic metallic ground state with properties that are consistent with the experimental results. The projected densities of states indicate that the main responsible for the magnetic moment observed in the Mn5Ge3 is the Mn-Mn interaction. The magnetic field distribution isosurfaces obtained from the DFT calculations offer a satisfactory explanation of the magnetic reversal experimentally observed, especially the in-plane magnetic behavior in samples grown on both GaAs(111) and GaAs(001) substrates. This work provides a theoretical-experimental approach that allows a deeper understanding of the magnetic anisotropy behavior under the influence of the crystallographic orientation of the substrate observed in nearly-stoichiometric Mn5Ge3 thin films, which is a good candidate for rare-earth free magnet in spintronic applications.

Tuning the Mn5Ge3 and Mn11Ge8 thin films phase formation on Ge(111) via growth process

We have studied the stability of manganese germanide thin films grown on Ge(111) substrates by three different growth methods: solid phase epitaxy, reactive deposition epitaxy and co-deposition. By combining X-ray diffraction and magnetic measurements, we demonstrate that we can form either Mn5Ge3 or Mn11Ge8 thin films depending on the growth processes. In the case of solid phase epitaxy, we explain the phase formation sequence by taking into consideration the kinetic and thermodynamic processes involved. Tuning phase formation of the manganese germanide thin films was determined using in situ X-ray diffraction and the effect of the thin film thickness on the Mn5Ge3 thermal stability was investigated.

The magnetic properties of Mn5Ge3 thin films grown on PMN-PT

The authors report the thickness dependent structural and magnetic properties of Mn5Ge3 thin films with different Mn layer thicknesses in the range from 5 nm to 30 nm deposited on Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) substrates using solid phase epitaxy. Gradual decrease of the surface roughness due to the formation of larger grains, as well as the decrease of the coercivity and squareness ratio on increasing of Mn layer thickness has been observed. It has been revealed that the slightly greater value of the saturation magnetization than the corresponding one observed early for thin films and bulk samples isassociated withthe presence ofstructural defects. The ferromagnetic resonance (FMR) spectra have been obtained to be isotropic for the films with 5 nm thickness, whereas those registered from the films with the thicknesses of 10 nm and above demonstrated in-plane magnetic anisotropy, which have been interpreted as to be resulted from magnetocrystalline anisotropy as well as the stress-induced magnetic anisotropy. These results are suggested to create a major interest in the development of magnetoelectric heterostructured devices based on strain coupling that are compatible with CMOS technology.

Magnetic and structural properties of Mn5+xGe3+y thin films as a function of substrate orientation

Mn5Ge3 thin films were grown on GaAs(111) and GaAs(001) by Molecular Beam Epitaxy (MBE). The influence of stoichiometry and alloying of the samples was investigated using different Mn diffusion cell temperatures for each sample. X-ray diffraction (XRD) measurements reveal the following epitaxial relations: (001) Mn5Ge3//(111) GaAs and [110] Mn5Ge3//[2–1–1] GaAs for the sample grown on GaAs(111), and (111) Mn5Ge3//(001) GaAs and [−110] Mn5Ge3//[110] GaAs for the samples grown on GaAs(001). High-resolution transmission electron microscopy (HRTEM) results for a sample grown on GaAs(001) indicate that samples are around 70 nm thick and are composed of several grains with 2 different orientations corresponding to a 90° rotation around the [111] axis. Analyzing the Mn map with energy-filtered transmission electron microscopy (EFTEM) we observed that all the grains look very similar, indicating that they contain roughly the same amount of manganese. The magnetocaloric effect found in both family of samples is spread in a wider temperature range when compared with bulk Mn5.1Ge2.9 and the magnetic entropy change peak is higher than Si- or Sb- modified Mn5Ge3. This result makes the Mn5Ge3 a possible candidate for magnetic refrigeration while being a rare earth-free material.

Strong magnetization and anisotropy of Mn5Ge3 thin films on Ge(001)

We report on the growth of Mn5Ge3 thin films on Ge(001) substrates following two methods: solid phase epitaxy (SPE) and reactive deposition epitaxy (RDE). We have varied the thickness of the films, in order to study the magnetization and anisotropy evolution. A strongly enhanced magnetization of 1580 kA m−1, compared to 1200 ± 150 kA m−1 for films grown on Ge(111), has been measured on ultrathin films of 5 nm grown by RDE. Thicker films exhibited magnetizations <750 kA m−1. The films grown by SPE also exhibit strong magnetization of 1490 kA m-1 and a drop of magnetization by increasing the film thickness. The effective magnetic anisotropy exhibits a more complex behavior: increases on the SPE films and decreases on the RDE films while increasing the thickness of the films. Magnetostatic and interfacial anisotropies were considered and calculated. The results are discussed in terms of the growth methods and microstructure of the films.

Carbon concentration, Curie temperature, and magnetic resonance field of Mn5Ge3(C) thin films

Carbon-doped Mn5Ge3 thin films were grown using magnetron sputtering and reactive diffusion or non-diffusive reaction (NDR). The C content, the Curie temperature, and the resonance field difference between the hard and easy axis were measured for all the films, allowing linear relations between these three parameters to be quantitatively determined. Thanks to these functions, the measurement of a single of these parameters allows the two others to be known. The association of the sputtering technique to the NDR process appears as the best way for producing C-doped Mn5Ge3 thin films.

Step flow growth of Mn5Ge3 films on Ge(111) at room temperature

The very first stages of the non-diffusive growth of Mn5Ge3 thin films on Ge(111) substrates are characterized by several techniques. Mn5Ge3 films are grown by molecular beam epitaxy using the co-deposition of Mn and Ge atoms at room temperature. XRD measurements demonstrate that the thin films are monocrystalline. The evolution of the RHEED intensity during the deposition and the AFM images show a step-flow growth mode. RHEED patterns, combined with TEM images, prove that the lattice mismatch of 3.7% is accommodated by the formation of an array of interfacial dislocations and by the presence of a residual strain in the thin films. These observations are supported by the numerical calculations of the critical nucleation volumes exhibiting very similar values, in the case of a pseudomorphic growth or in the case of an accommodation of the lattice mismatch by interfacial dislocations. Furthermore, the effect Ge/Mn stoichiometric and Mn-rich fluxes on the surface morphology is examined.

Carbon Concentration, Curie Temperature, and Magnetic Resonance Field of Mn5ge3(C) Thin Films

Carbon-doped Mn5Ge3 thin films were grown using magnetron sputtering and reactive diffusion or non-diffusive reaction (NDR). The C content, the Curie temperature, and the resonance field difference between the hard and easy axis were measured for all the films, allowing linear relations between these three parameters to be quantitatively determined. Thanks to these functions, the measurement of a single of these parameters allows the two others to be known. The association of the sputtering technique to the NDR process appears as the best way for producing C-doped Mn5Ge3 thin films.

Epitaxial Mn5Ge3 (100) layer on Ge (100) substrates obtained by flash lamp annealing

Mn5Ge3 thin films have been demonstrated as promising spin-injector materials for germanium-based spintronic devices. So far, Mn5Ge3 has been grown epitaxially only on Ge (111) substrates. In this letter, we present the growth of epitaxial Mn5Ge3 films on Ge (100) substrates. The Mn5Ge3 film is synthetized via sub-second solid-state reaction between Mn and Ge upon flash lamp annealing for 20 ms at the ambient pressure. The single crystalline Mn5Ge3 is ferromagnetic with a Curie temperature of 283 K. Both the c-axis of hexagonal Mn5Ge3 and the magnetic easy axis are parallel to the Ge (100) surface. The millisecond-range flash epitaxy provides a new avenue for the fabrication of Ge-based spin-injectors fully compatible with CMOS technology.

Effect of Ge layer thickness on the formation of Mn5Ge3 thin film on Ge/Si (1 1 1)

Abstract The effect of Ge buffer layer thickness on the formation of epitaxial Mn5Ge3 films and their magnetic properties has been investigated. Epitaxial ferromagnetic Mn5Ge3 thin films were deposited on Ge/Si (1 1 1) substrates using solid phase epitaxy. The crystalline quality, chemical composition and magnetic properties of the films were investigated by x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy, electron spin resonance. Increasing the thickness of the Ge layer significantly enhanced the crystallinity and magnetic homogeneity of Mn5Ge3 films. Both structural and magnetic investigations show substantial diffusion of Mn atoms through Ge buffer layer which results in the formation of Mn5Si3 and a delay in Mn5Ge3 formation until the thickness of the Ge layer reaches to 70 nm. The observed magnetic behavior for the films grown on different Ge thicknesses is interpreted in terms of changes in the magnetic phases and surface properties. These results show that Mn5Ge3 can be epitaxially grown on Si substrate with Ge buffer layer thicknesses of above 140 nm, despite ∼8% lattice mismatch between Mn5Ge3 and Si (1 1 1).

Epitaxial mosaic-like Mn5Ge3 thin films on Ge(001) substrates

Epitaxial mosaic-like Mn5Ge3 thin films were grown on Ge(001) substrates using reactive deposition epitaxy process from Mn deposition or Mn-Ge co-deposition at a substrate temperature of 250 °C using magnetron sputtering. The cross-sectional transmission electronic microscopy analyses reveal an abrupt interface at the atomic scale; two equivalent epitaxial relationships are found between the substrate and the Mn5Ge3 crystallites: Ge(001)[110] and [11¯0]∥ Mn5Ge3(11¯1)[1¯1¯0]. The chex axis of Mn5Ge3 forms an angle of 45° with the substrate plane. Rietveld analysis from a synchrotron 2-dimensional diffraction pattern revealed that remanent deformations of about 1% exist in the film. M-H measurements of 50-nm thick films elaborated by co-deposition revealed a saturation magnetization, Ms, of 636 kAm−1, whereas the films elaborated by Mn deposition saturate at different values depending on the orientation of the applied magnetic field: Ms⊥ = 545 kAm−1 and Ms∥ = 774 kAm−1. This Ms difference is attributed to shape anisotropy of crystallites and interface quality of the films.

Thiol-functionalization of Mn5Ge3 thin films

Hybrid organic/inorganic interfaces could pave the way to chemically designed or new multifunctional electronic devices, in particular in the spintronics field where, for instance, the interfacial spin polarization can be tuned through chemical interactions and surface modifications. We report herein, for the very first time, the assays of self-assembled monolayers (SAMs) formation on Mn5Ge3 surface. Interestingly, Mn5Ge3 is a ferromagnetic metal possessing interesting features for spintronics such as a high Curie temperature, a capability to grow epitaxially on Ge germanium that is a key point for integration in the mainstream Si technology. Mn5Ge3 thin films are synthesized by molecular beam epitaxy under ultra-vacuum condition. We studied the Mn5Ge3 surface prior to deposition of SAMs, meaning the surface exposed to air and different solvents, by XPS and contact angle measurements leading to the value of the surface tension of this surface. Then SAMs of octanethiol and perfluorodecanethiol are formed on Mn5Ge3 surface at room temperature. The best experimental conditions to form the SAMs are found for an immersion time of 36 h and a concentration of 4 mM.

High-temperature dependence of low magnetization Mn5Ge3 phase formation of sputtered thin films

We report on the high-temperature dependence of the Mn5Ge3 phase formation on Ge(001). High substrate temperatures from 650 to 850 °C lead to the formation of the Mn5Ge3 thin films with a low magnetization of ~250 kAm-1, which is an important characteristic for faster and low energy consumption of the switching of the magnetic orientation of magnetic thin films by spin-transfer torque. The highest temperature conducts to the formation of the Mn5Ge3 phase with only a small amount of Mn5Ge2 hexagonal clusters. Additionally, carbon doping of the Mn5Ge3 sample grown at 750 °C exhibits an enhancement of the Curie temperature from 296 K to 390 K. The growth mechanism corresponds to a Volmer-Weber mode.

High Curie temperature Mn5Ge3 thin films produced by non-diffusive reaction

Polycrystalline Mn5Ge3 thin films were produced on SiO2 using magnetron sputtering and reactive diffusion (RD) or non-diffusive reaction (NDR). In situ X-ray diffraction and atomic force microscopy were used to determine the layer structures, and magnetic force microscopy, superconducting quantum interference device, and ferromagnetic resonance were used to determine their magnetic properties. RD-mediated layers exhibit similar magnetic properties as molecular beam epitaxy-grown monocrystalline Mn5Ge3 thin films, while NDR-mediated layers show magnetic properties similar to monocrystalline C-doped Mn5Ge3Cx thin films with 0.1 ≤ x ≤ 0.2. NDR appears as a complementary metal oxide semi-conductor-compatible efficient method to produce good magnetic quality high-Curie temperature Mn5Ge3 thin films.

Role of the substrate temperature on the growth of Mn5Ge3 thin films by co-deposition of Mn and Ge on Ge(001) substrates by magnetron sputtering

Mn5Ge3 thin films grown on Ge(001) substrates were obtained by co-deposition of pure Mn and Ge elements using rf-magnetron sputtering at different substrate temperatures, Ts (250°C≤Ts≤550°C) in order to analyze the influence of the substrate temperature on the structural and magnetic properties of the samples. These films were thoroughly studied by reflection high-energy electron diffraction, transmission electron microscopy, atomic force microscopy, and SQUID magnetometry, evidencing the important role of the substrate temperature on the microstructure of the films. For temperatures higher or equal to 350°C, a crystalline Mn11Ge8 phase also appears in addition of the Mn5Ge3 one, evidenced by the diffraction and magnetic measurements. Additionally, spin-glass-like magnetic behavior is also observed in all the samples (more evident when the Mn11Ge8 phase is small), due to the existence of a layer with spin-glass properties at the Ge/Mn5Ge3 interface caused by the intermixing of Ge and Mn at that interface.

Ferromagnetic resonance and magnetic damping in C-doped Mn5Ge3

Ferromagnetic resonance (FMR) was used to investigate the static and dynamic magnetic properties of carbon-doped Mn5Ge3 thin films grown on Ge(1 1 1). The temperature dependence of magnetic anisotropy shows an increased perpendicular magneto-crystalline contribution at 80 K with an in-plane easy axis due to the large shape contribution. We find that our samples show a small FMR linewidth (corresponding to an intrinsic magnetic damping parameter ) which is a measure of the spin relaxation and directly related with the magnetic and structural quality of the material. In the perpendicular-to-plane geometry, the FMR linewidth shows a minimum at around 200 K for all the samples, which seems to be not correlated to the C-doping. The magnetic relaxation parameters have been determined and indicate the two-magnon scattering as the main extrinsic contribution. We observe a change in the main contribution from scattering centres in Mn5 Ge3C0.2 at low temperatures, which could be related to the minimum in linewidth.

Magnetic reversal in Mn5Ge3 thin films: an extensive study

We present a comprehensive study of magnetization reversal process in thin films of . For this investigation, we have studied the magnetic anisotropy of layers as a function of the film thickness using VSM and SQUID magnetometers. The samples grown by molecular beam epitaxy exhibit a reorientational transition of the easy axis of magnetization from in-plane to out-of-plane as the film thickness increases. We provide evidence that above a critical thickness estimated as 20 nm, the magnetic structure is most probably constituted of stripes with out-of-plane magnetization pointing alternately up and down. We have analyzed our results using different phenomenological models and all the calculations converge towards values for magnetocrystalline anisotropy constant and saturation magnetization that are in excellent agreement with the reported values for bulk . This study has also led to the first estimation in of the exchange constant, the surface energy of domain walls as well as their width. These parameters are essential for determining whether this material can be used in the next generation of spintronic devices.

K dependence of the spin polarization inMn5Ge3/Ge(111)thin films

Mn5Ge3(001) thin films grown on Ge(111) were studied by angle-and spin-resolved photoemission using synchrotron radiation in the 17-40 eV photon energy range. The photoelectron spectra were simulated starting from a first-principles band-structure calculation for the ground state, using the free-electron approximation for the final states, taking into account photohole lifetime effects and k(perpendicular to) broadening plus correlation effects, but ignoring transition matrix elements. The measured spin polarizations for the various k points investigated in the Gamma MLA plane of the Brillouin zone are found to be in fair enough agreement with the simulated ones, providing a strong support to the ground-state band-structure calculations. Possible origins for the departures between either simulations and experiments or previous and present experiments are discussed. (Less)

Strain-induced modification in the magnetic properties of Mn5Ge3 thin films

Epitaxial ferromagnetic Mn5Ge3 thin films were stabilized on GaSb(001) and GaAs(001) substrates using molecular beam epitaxy. Compared to bulk Mn5Ge3 materials, an enhancement of the Curie temperature above 350 K and about 320 K was observed for Mn5Ge3/GaAs(001) and Mn5Ge3/GaSb(001) heterostructures, respectively. The magnetization was found to decrease from 323 to 245 emu/cm3 for films grown on GaSb(001) and GaAs(001). Anomalous Hall effect measurements provide evidence of the strain-induced large spin polarization from density-functional study. Furthermore, our calculated results in bulk Mn5Ge3 under strain indicate that the strain is the origin of different physical properties of Mn5Ge3 grown on different substrates.