FeMn Films Research Articles

Preparation and characterization of ferrous manganese thin films for magnetic storage devices

The nanocrystalline nature of Ferrous Manganese (Fe-Mn) thin film coatings was obtained from sulphate baths at different current densities on the copper substrate. The effects of current density on structure, surface morphology, elemental composition, magnetic properties, and mechanical properties of electrodeposited Fe-Mn magnetic films were studied. The structural and surface properties of Fe-Mn thin films were studied using an Xray Diffractometer (XRD) and Scanning Electron Microscopy (SEM). The chemical compositions of the deposited films were investigated using Energy Dispersive X-ray Spectroscopy (EDAX). The magnetic properties of the thin films were studied with the aid of a Vibrating Sample Magnetometer (VSM). The electrodeposited Fe-Mn films were found to be nanocrystalline in nature due to the increase in current density. The deposits of Fe-Mn thin films were found to have a crack-free and smooth surface at low current densities. The films have good adherence to the copper substrate.

Stress-induced Néel vector reorientation in γ -FeMn antiferromagnetic thin films

The relationship between stresses and the orientation of the Néel vector were studied by varying the residual stresses in magnetron sputtered FeMn thin films by adjusting Argon working pressures. Quasistatic magnetization and AC susceptibility measurements reveal that the FeMn film with compressive stress (−27 MPa/−0.015% strain) possesses an out-of-plane Néel vector orientation with a 44 kOe spin-flop field, as contrasted to the FeMn film with tensile stress (25 MPa/0.014% strain) showing an in-plane orientation with a 34 kOe spin-flop field. An energy formulation for the films estimates a magnetostriction value of 109 ppm following an effective anisotropy of −8 kJ/m3. The film with the larger residual stress (77 MPa/0.043% strain) displayed a strain-induced phase transition from γ-FeMn to α-FeMn. These results show the dependency of the Néel vector on the stress state indicative of relatively large magnetostriction.

Appearance of Intrinsic Magnetization in FeMn Antiferromagnetic Film under the Action of Spin-Polarized Current

The article presents the results of research of two spin-injection sources of THz radiation using different structures of thin-film magnetic transitions (MT) with antiferromagnetic (AFM) FeMn film of nanoscale thickness and ferromagnetic (FM) Fe layer. In both variants, the possibility of intrinsic magnetization forming in the AFM film under the action of a spin-polarized current of a relatively small value formed in the FM layer is shown. The physical foundations of this effect based on the AFM sublattices beveling by a spin-polarized current due to the sd-exchange interaction of the conduction electrons spins with the spins of d electrons of the FM crystal lattice are considered. This does not require an external magnetic field. sd-exchange mechanism of excitation of intrinsic magnetization in AFM is an alternative to the spin-orbit mechanism, which has been widely considered recently. The relations for calculating the frequency and power of spin-injection radiation are given. New experimental results have been obtained that develop the concept of the AFM's intrinsic magnetization. The non-thermal nature of spin-injection radiation and the possibility of increasing the efficiency of the emitter operation due to the ordering of the MT structure by an external magnetic field are shown. The way of increasing the efficiency of spin-injection emitters by creating structures with multiple independently operating micro-emitters at frequencies close to 16 THz and with a signal power of up to a hundred microwatts has been determined. In general, it is shown that the use of the effect of excitation of intrinsic magnetization in AFM is of interest, both from the point of view of the development of theoretical ideas about the magnetic properties of AFM, and from a practical point of view for the creation of spin-injection lasers (tasers).

Regulation of Microstructure, Static, and Microwave Magnetic Performance of NiFe/FeMn/NiFe Heterogeneous Multilayer Films Based on Thickness of FeMn Films

Ferromagnetic (FM)/antiferromagnetic (AFM) heterogeneous multilayer films have triggered tremendous interests for application in microwave/mm devices and components. However, with the development trend of miniaturization, high frequency, and lightweight of devices, the FM/AFM heterogeneous multilayers are desired to possess high saturation magnetization (4πMs), low coercivity (Hc), and low ferromagnetic resonance (FMR) linewidth (∆H). Herein, the Ni81Fe19 (50 nm)/Fe50Mn50 (t nm)/Ni81Fe19 (50 nm) films were fabricated by DC magnetron sputtering, and the effects of thickness of the Fe50Mn50 on the microstructure, static, and microwave properties were investigated in detail. With increasing the FeMn film thickness, the saturation magnetization firstly increased and then decreased from 7947 to 9448 Gs. The in-plane coercivity firstly decreased and then increased from 28.58 to 0.6115 Oe, and the out-of-plane exchange bias field undergoes a transition from a negative exchange bias to a positive exchange bias. Besides, the ferromagnetic resonance linewidth firstly decreased and then increased from 142 to 87 Oe. Remarkably, with a 15-nm Fe50Mn50 film, the heterogeneous multilayer films achieved optimum performance with high saturation magnetization (9448 Gs), low coercivity (1.02 Oe), and low FMR linewidth (94 Oe). The outstanding Ni81Fe19/Fe50Mn50/Ni81Fe19 heterogeneous multilayer films exhibit great potentials in radar remote sensing, communication, and electronic countermeasure fields.

Magnetic characteristics of Guangshan loess from northern piedmont of Dabie Mountains, east-central China

SUMMARY The loess from the northern piedmont of the Dabie Mountains is in a transition area between loess from the Chinese Loess Plateau, the Quaternary red soils of southern China and the Xiashu loess. Despite its significant location, the study has been inadequate. In this study, the Guangshan section in the northern piedmont of the Dabie Mountains was selected for investigation. Environmental magnetism, geochemistry, colour reflectance and optical diffuse reflection spectroscopy analyses were applied to detect the magnetic variations in the loess. The results showed that (1) the magnetic minerals consisted mainly of magnetite, maghemite, hematite and goethite, which are the same as those in the Quaternary loess from the Chinese Loess Plateau, the Xiashu loess and the Quaternary red soils of southern China. The average magnetic particles were in the pseudo-single domain, like those of the Chinese Loess Plateau loess. (2) Unit III of the Guangshan section (2.4–4 m), with high chemical index of alteration and low Ba-index, was demonstrated as the most strongly developed palaeosol in the whole section, in agreement with field observations (more Fe-Mn films and weakly vermiculated development). However, it exhibited minimal susceptibility values and the lowest concentration of fine ferrimagnetic minerals. Simultaneously, the unit had low hematite to goethite ratio (Hm/Gt), suggesting that the pedogenic environment was humid; and it also had high values of b* and Gt%, implying that there was more goethite. Therefore, we can conclude that excessive soil moisture and intensive pedogenesis dissolved the fine ferrimagnetic minerals originally produced by pedogenesis and transformed them into goethite. These results could help to trace the palaeoclimatic evolution of the study area and clarify the magnetic variations of loess in different climates throughout China.

Analysis of the electrodeposition process of Fe–Mn films from sulfate electrolytes

Fe–Mn alloys with different composition and structure have great importance in a wide range of applications, which requires a detailed knowledge of a variety of production methods. In the present work, Fe–Mn thin films were electrochemically deposited from sulfate aqueous solutions under different conditions on Cu substrates. The effects of several applied potentials for deposition, concentrations of reagents and speed of rotation of the electrode were investigated. Chronoamperometry tests were performed and the curves obtained were analyzed through the models for nucleation and growth from Scharifker et al and from Isaev et al considering apparent diffusion coefficient for the deposition of the alloy. The approach with both these models point to a process close to the instantaneous nucleation limit. Globally, the results indicate a mixed transport-kinetic control for most of the conditions, but a behavior with characteristics of diffusion controlled growth can be established for specific conditions of speed of rotation and concentrations. Koutechký-Levich analysis has been applied to current-potential curves at the rotating-disk electrode providing the determination of the apparent diffusion coefficients and heterogeneous rate constants for electron transfer. Fe is preferentially deposited with a much higher rate of reduction than Mn in the employed solutions. The whole deposition process is very sensitive to the presence of (NH4)2SO4, which affects also the quality of the deposits. The samples were further characterized by scanning electron microscopy and x-ray dispersive energy spectroscopy.

Comparative study of the sustainable preparation of FeMn thin films via electrodeposition and magnetron co-sputtering

Biodegradable electronic devices based on non-toxic materials are an emerging field, in which the key characteristic is the complete dissolution of the devices within a determined period of time. Usually, these devices are built on polymer substrates or pure metals; however they present some disadvantages such as low degradation rate. The present study reports and compares the sustainable preparation of FeMn films via electrodeposition and magnetron co-sputtering as a possible alternative to the aforementioned materials. Morphological, chemical, structural and magnetic characterization of the obtained layers was carried out and the corrosion and biocompatibility characteristics were assessed by electrochemical studies and cell viability assays. Different ratios of Mn2+:Fe2+ ions in the electrolyte leaded to metallic and oxide based FeMn layers. The electrodeposited FeMn films showed different crystalline structure depending on their nature: a bcc-Fe crystal structure when they are metallic and fcc when they are oxidized. In addition, glycine was used as complexing agent in the electrolytic bath, which leaded to less-crack films and varied the Mn content in the films (9–24 wt%). The Mn content of the magnetron co-sputtered films varied between 10 and 70 wt%. Differently to the electrodeposited films, the sputtered revealed a well-defined bcc structure that lowers its symmetry when the Mn content increases. Regarding the magnetic behavior, all obtained films showed a soft magnetic behavior. Their corrosion behavior in NaCl solutions was evaluated by electrochemical studies, observing a shift to more negative corrosion potential values when Mn content increases. In vitro cytotoxicity tests revealed highly biocompatible characteristics with a cell viability of 85% even for the Mn-richest sputtered films (70 wt%) while electrodeposited films showed a clear indication of toxicity.

Ab Initio Guided Low Temperature Synthesis Strategy for Smooth Face–Centred Cubic FeMn Thin Films

The sputter deposition of FeMn thin films with thicknesses in the range of hundred nanometres and beyond requires relatively high growth temperatures for the formation of the face-centred cubic (fcc) phase, which results in high thin film roughness. A low temperature synthesis strategy, based on local epitaxial growth of a 100 nm thick fcc FeMn film as well as a Cu nucleation layer on an α-Al2O3 substrate at 160 °C, enables roughness values (Ra) as low as ~0.6 nm, which is in the same order of magnitude as the pristine substrate (~0.1 nm). The synthesis strategy is guided by ab initio calculations, indicating very strong interfacial bonding of the Cu nucleation layer to an α-Al2O3 substrate (work of separation 5.48 J/m²)—which can be understood based on the high Cu coordination at the interface—and between fcc FeMn and Cu (3.45 J/m²). Accompanied by small lattice misfits between these structures, the strong interfacial bonding is proposed to enable the local epitaxial growth of a smooth fcc FeMn thin film. Based on the here introduced synthesis strategy, the implementation of fcc FeMn based thin film model systems for materials with interface dominated properties such as FeMn steels containing κ-carbide precipitates or secondary phases appears meaningful.

Ferromagnetic phase in partially oxidized FeMn films

The structure, magnetic and magnetoresistive properties of ferromagnetic phase in partially oxidized FeMn films was studied. The oxidation was performed by annealing of the samples under atmospheric pressure in a gas mixture (nitrogen with 0.5% oxygen) at the temperature of 300 °C. The resulting ferromagnetic phase was isotropic in the film plane. The value of the anisotropic magnetoresistance was similar to the value of the anisotropic magnetoresistance usually observed in films of pure iron. The oxidation of antiferromagnetic FeMn films resulted in the appearance of an exchange bias.

Noncollinear magnetic structures of FeMn ultrathin films on Cu(001)

We investigate, by means of ab initio spinor-density-functional calculations, the magnetic structures of one and two monolayers of MnFe ordered alloys on the Cu(001) surface. For comparison, we also examine the FeMn compound with L10 structure, as bulk reference limit of the FeMn films. In the limit of the ultrathin films considered, the 3Q antiferromagnetic ground state of the FeMn bulk is unstable. A strongly non-collinear planar ferro- or ferri-magnetic spin structure is established, instead, as ground state. It is characterised by mainly parallel alignments of the Fe spins and Mn-Fe spins with orientations close to perpendicular. Depending on the Mn/Fe chemical order and coordination, the Fe-Mn exchange coupling is either antiferromagnetic or ferromagnetic biased. The trends of the spin structure and Fe-Mn exchange coupling with different chemical orders and thicknesses of the films are discussed based on the calculated Fe and Mn local density of states. In particular, the behaviour of the Fe-Mn exchange coupling is found to be controlled mainly by the position of the Fermi energy within the Fe-3d minority-spin local density of states.

Strong modification of intrinsic spin Hall effect in FeMn with antiferromagnetic order formation

FeMn films with and without a Cu seed layer were deposited on Y3Fe5O12 (YIG) substrates, and their inverse spin Hall effect (ISHE) was examined through both spin Seebeck effect and spin pumping.

Antiferromagnetic FeMn alloys electrodeposited from chloride-based electrolytes.

The capability of synthesizing Fe-based antiferromagnetic metal alloys would fuel the use of electrodeposition in the design of new magnetic devices such as high-aspect-ratio spin valves or new nanostructured hard magnetic composites. Here we report the synthesis of high quality antiferromagnetic FeMn alloys electrodeposited from chloride-based electrolytes. We have found that in order to grow homogeneous FeMn films it is necessary to incorporate a large concentration of NH4Cl as an additive in the electrolyte. The study of the structure and magnetic properties shows that films with composition close to Fe50Mn50 are homogeneous antiferromagnetic alloys. We have established a parameter window for the synthesis of FeMn alloys that show antiferromagnetism at room temperature.

Exchange bias ofTbPc2molecular magnets on antiferromagnetic FeMn and ferromagnetic Fe films

Improving the magnetic stability of single-molecule magnets is a key challenge facing molecular spintronics. We use x-ray magnetic circular dichroism to explore the possibility of magnetically stabilizing ${\mathrm{TbPc}}_{2}$ molecules by attaching them to ultrathin Fe and FeMn films. We show that ${\mathrm{TbPc}}_{2}$ deposited on antiferromagnetic FeMn films exhibits magnetic hysteresis and exchange bias as a consequence of coupling to the uncompensated interfacial Fe spins. The FeMn-thickness dependence of the coercive field and exchange bias of ${\mathrm{TbPc}}_{2}$ is similar to that of inorganic ferromagnetic/antiferromagnetic systems. The magnetic remanence is comparable with the fraction of molecules attached to pinned interfacial Fe spins. The Tb magnetic moments are antiferromagnetically coupled to the Fe thin films as well as to the uncompensated Fe spins at the FeMn interface. The sign of the coupling changes from antiferromagnetic to ferromagnetic after doping the interface with electron-donor Li atoms.

Terahertz emission in the ferromagnetic-antiferromagnetic structure

Current flow in the structure consisting of a hard-magnetic ferromagnetic rod (hardened steel) with a diameter of up to 100 μm that contacts a thin (10–100 nm) ferromagnetic (FeMn) film is studied at room temperature. Effective magnetization is induced in the FeMn film in the presence of the spin-polarized current in spite of the absence of the intrinsic magnetization. The terahertz radiation that is detected in this work is caused by the precession of the induced magnetization. The emission is interpreted using the recent theoretical predictions on the effect of the sd exchange on the lattice dynamics of antiferromagnetic layer.

Ta/NiFe/FeMn thin films with enhanced exchange bias prepared at room temperature by rotational deposition

Ta(20nm)/NiFe(5nm)/FeMn(20nm) films were deposited on glass substrates by rotational deposition at room temperature. A significant enhancement in the exchange bias field (Heb) associated with very low coercivity (Hc) was achieved for the samples prepared at rotational speed (Rrpm) of 1rpm. The Heb and Hc of the samples with Rrpm=1rpm were approximately double and smaller than half of those deposited by conventional continuous sputtering, respectively. Structural studies reveal that the rotational deposition not only improves the crystallization of FeMn but also facilitates the development of (111) texture through a preferred Ta(200) orientation. The sputtering powers of the constituent layers: WTa, WNiFe and WFeMn significantly affected the magnetic properties. Remarkable exchange bias properties, such as Heb of 26.67kA/m and Hc of 1.99kA/m were achieved at Rrpm=1rpm, WTa=40W, WNiFe=70W and WFeMn=140W. The Heb value obtained with the Ta/NiFe/FeMn films is comparable to that with the commercialized NiFe/IrMn system with a similar layered structure and it is more than 3 times larger than that of the sample deposited with fixed substrate in this study. The intensity of the FeMn(111) peak and the Scherrer coherent length are proportional to the Heb, indicating that the exchange bias behavior of the sample was dominated by the stability of the antiferromagnetic spin structure. The rotational deposition method proposed in this study favors practical applications in terms of both production cost and performance of spintronic devices.

Construction of the Magnetic Phase Diagram of FeMn/Ni/Cu(001) Using Photoemission Electron Microscopy

Single crystalline FeMn/Ni bilayer was epitaxially grown on Cu(001) substrate and investigated by photoemission electron microscopy (PEEM). The FeMn and Ni films were grown into two cross wedges to facilitate an independent control of the FeMn (0-20 ML) and Ni (0-20 ML) film thicknesses. The Ni magnetic phases were determined by Ni domain images as a function of the Ni thickness (d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ni</sub> ) and the FeMn thickness (d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FeMn</sub> ). The result shows that as the Ni thickness increases, the Ni film undergoes a paramagnetic-to-ferromagnetic state transition at a critical thickness of d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FM</sub> and an in-plane to out-of-plane spin reorientation transition at a thicker thickness d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SRT</sub> . The phase diagram shows that both d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FM</sub> and d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SRT</sub> increase as the FeMn film establishes its antiferromagnetic order.

Exploring the limits of soft x-ray magnetic holography: Imaging magnetization reversal of buried interfaces (invited)

Only a very few experimental techniques can address the microscopic magnetization reversal behavior of the different magnetic layers in a multilayered system with element selectivity. We present an element-selective study of ferromagnetic (FM) [Co/Pt]n multilayers with perpendicular anisotropy exchange-coupled to antiferromagnetic (AFM) FeMn and IrMn films performed with a new experimental set-up developed for both soft x-ray spectroscopy and holography imaging purposes. The spectroscopy analysis allows the quantification of the unpinned (pinned) uncompensated AFM moments, providing direct evidence of its parallel (antiparallel) alignment with respect to the FM moments. The holography experiments give a direct view of both FM and uncompensated AFM magnetic structures, showing that they replicate to each other during magnetization reversal. Remarkably, we show magnetic images for effective thicknesses as small as one monolayer. Our results provide new microscopic insights into the exchange coupling phenomena and explore the sensitivity limits of these techniques. Future trends are also discussed.

Magnetic interaction in exchange-biased bilayers: a first-order reversal curve analysis

The distributions of coercivities and magnetic interactions in a set of polycrystalline Ni0.8Fe0.2/FeMn bilayers have been determined using the first-order reversal curve (FORC) formalism. The thickness of the permalloy (Py) film was fixed at 10 nm (nominal), while that of the FeMn film varied within the range 0–20 nm. The FORC diagrams of each bilayer displayed two clearly distinguishable regions. The main region was generated by Py particles whose coercivities were enhanced in comparison with those in which the FeMn film was absent (sample O). The minor region was produced by Py particles with coercivities similar to or slightly higher than those of particles in the Py film of sample O. Each sample presented two distributions of interaction fields, one for each region, and both were centred slightly below the exchange-bias field, thus indicating a prevalence of magnetizing interactions. These results are consistent with a grain size distribution in the Py layer and the presence of uncompensated antiferromagnetic moments.

Enhanced magnetic properties of cobalt nanoparticles on FeMn films

Monodisperse cobalt nanoparticles are synthesized by the thermal decomposition of Co 2(CO) 8 in phenyl ether and subsequently deposited on antiferromagnetic (AFM) FeMn films and glass substrates, respectively. Magnetic measurement shows that the as-prepared Co nanoparticles are superparamagnetic and can be transformed into ferromagnetic (FM) through thermal treatment. While keeping monodisperse, the annealed FM Co nanoparticles on AFM FeMn films show a much larger coercivity than the ones on glass substrates due to FM/AFM exchange coupling. Accordingly, we propose a convenient method to enhance magnetic properties of nanoparticles.

Asymmetry in the dynamics of domain walls in thin exchange-coupled ferromagnetic films

The kinetics of remagnetization after magnetic field switching was studied by the magneto-optic visualization technique in the bilayer hybrid structure composed of exchange-coupled FeNi and FeMn films. It was observed that not only the static but the dynamic characteristics of remagnetization as well depend on the polarity of a field applied along the direction of easy magnetization. The rate of the process was found to be exponentially dependent on the field strength in both directions, but the rate varied by factors of 10 upon inversion of the field. It was shown that this difference is the consequence of variation of both the time of domains nucleation and the velocity of domain walls motion.