Electric-field control of magnetism via inverse magnetostrictive effect is an efficient path towards improving energy-efficient storage and sensing devices based on giant magnetoresistance effect. In this letter, we report on lateral electric-field driven strain-mediated modulation of magnetic properties in Co/Cu/Py pseudo spin valve grown on ferroelectric PMN-PT substrate. We show a decrease of the giant magnetoresistance ratio of the pseudo spin valve with increasing electric field, which is attributed to the deviation of the Co layer magnetization from the initial direction due to strain-induced magnetoelastic anisotropy contribution. Additionally, we demonstrate that strain-induced magnetic anisotropy effectively shifts the switching field of the magnetostrictive Co layer, while keeping the switching field of the nearly zero-magnetostrictive Py layer unaffected due to its negligible magnetostriction constant. We argue that magnetostrictively optimized magnetic films in properly engineered multilayered structures can offer a path to enhancing the selective magnetic switching in spintronic devices.

Evaluating the thermal processes occurring inside an illuminated nanoscale semiconducting tip is of utmost importance for the physical understanding of laser assisted atom probe tomography (L-APT). In this paper, we present a methodology to evaluate the temperature at the apex of the tip using L-APT. The method is based on the known exponential dependence of the probability for field evaporation on the temperature and the electric field at the apex. We use this method to gain insights into the effect of tip shape, doping, and laser power on the peak temperature reached at the apex of an illuminated Si tip.

We present an optically induced remanent photostriction in BiFeO_{3}, resulting from the photovoltaic effect, which is used to modify the ferromagnetism of Ni film in a hybrid BiFeO_{3}/Ni structure. The 75% change in coercivity in the Ni film is achieved via optical and nonvolatile control. This photoferromagnetic effect can be reversed by static or ac electric depolarization of BiFeO_{3}. Hence, the strain dependent changes in magnetic properties are written optically, and erased electrically. Light-mediated straintronics is therefore a possible approach for low-power multistate control of magnetic elements relevant for memory and spintronic applications.

Ge(1-x)Sn(x) has received a lot of interest for opto-electronic applications and for strain engineering in advanced complementary-metal-oxide-semiconductor technology, because it enables engineering of the band gap and inducing strain in the alloy. To target a reliable technology for mass application in microelectronic devices, the physical problem to be addressed is to unravel the complex relationship between strain relaxation (as induced by the growth of large layer thicknesses or a thermal anneal) and defect formation, and/or stable Sn-cluster formation. In this paper, we study the onset of Sn-cluster formation and its link to strain relaxation using Atom Probe Tomography (APT). To this end, we also propose a modification of the core-linkage [Stephenson et al., Microsc. Microanal. 13, 448 (2007)] cluster analysis method, to overcome the challenges of limited detection efficiency and lateral resolution of APT, and the quantitative assessment for very small clusters (<40 atoms) embedded in a random distribution of Sn-atoms. We concluded that the main relaxation mechanism for these layers is defect generation (misfit dislocations, threading dislocations, etc.), irrespective of the cause (thickness of layer or thermal anneal) of relaxation and is independent of the cluster formation. The low thermodynamic solubility limit of Sn in Ge seems to be the driving force for Sn-cluster formation. Finally, we also discuss the spatial distribution of Sn in clusters and relate them to the theoretically predicted stable Sn clusters [Ventura et al., Phys. Rev. B 79, 155202 (2009)]. (c) 2015 AIP Publishing LLC.

Electric control of magnetic properties is an important challenge for modern magnetism and spintronic development. In particular, an ability to write magnetic state electrically would be highly beneficial. Among other methods, the use of electric field induced deformation of piezoelectric elements is a promising low-energy approach for magnetization control. We investigate the system of piezoelectric substrate Pb[ZrxTi1-x]O3 with CoFe overlayers, extending the known reversible bistable electro-magnetic coupling to surface and multistate operations, adding the initial state reset possibility. Increasing the CoFe thickness improves the magnetoresistive sensitivity, but at the expenses of decreasing the strain-mediated coupling, with optimum magnetic thin film thickness of the order of 100 nm. The simplest resistance strain gauge structure is realized and discussed as a multistate memory cell demonstrating both resistive memory (RRAM) and magnetoresistive memory (MRAM) functionalities in a single structure.

A granular Cu80Co20 alloy was elaborated by a low cost electrodeposition technique consisting in reducing simultaneously the Cu2+ and Co2+ ions onto a silicon substrate. The deposition parameters were determined from current-potential curves. The structure of the film was characterized down to the atomic scale by transmission electron microscopy and atom probe tomography. The results show that the asdeposited Cu80Co20 thin film consists mainly of a paramagnetic Cu-Co solid solution containing 10-30% of Co, in which pure Co superparamagnetic nanoparticles are dissolved. Annealing at 500 degrees C for 1 h leads to the decomposition of the Cu-Co solid solution into purified Cu matrix containing ferromagnetic Co-rich precipitates. The magnetoresistance effect decreases after the heat treatment, in relation with the disappearance of the superparamagnetic Co nanoparticles upon annealing. (C) 2014 Elsevier B. V. All rights reserved.

Equiatomic FeAu nanoclusters were produced by inert-gas condensation and embedded in a W matrix. Transmission electron microscopy investigation shows that three kinds of clusters are present: mono-crystalline, polycrystalline, and partially crystalline clusters. It demonstrates that during their formation, the structure of nanoclusters evolves from an amorphous to a crystalline structure. Crystallisation starts at the surface of nanoclusters and currently leads to the formation of poly-crystalline nanoclusters in the end. Most of the investigated objects consist in a duplex amorphous core-crystalline shell structure. Their magnetic properties were investigated by magnetization measurements as a function of magnetic field (hysteresis loops) or temperature (ZFC/FC curves). They show evidence at low temperatures of ferromagnetic and antiferromagnetic states, and ordering as well as superparamagnetism or spin-glass behaviour. Measurements performed after cooling the samples under various applied fields reveal the occurrence of exchange-spring phenomenon, related to the presence of the W matrix, through RKKY coupling between ferromagnetic and antiferromagnetic nanoclusters.

Multilayered Cu/Co nanowires were elaborated by a low cost electrochemical technique consisting in reducing alternatively the Cu2+ and Co2+ ions, through a porous commercial anodic aluminum oxide template, onto a conductive substrate. The deposition parameters were determined from current-potential curves. The structure of the nanowires was characterized down to the atomic scale by transmission electron microscopy and atom probe tomography. The results show that the multilayers are polycrystallized with a nanometric grain size. The Cu layers are almost pure, while the Co ones consist in a Co-rich alloy with about 12 to 15% Cu.

The structural changes upon milling and subsequent annealing of a Mn54Al43C3 alloy containing the intermetallic tetragonal L1(0) MnAl phase (tau phase) as the major phase were investigated by X-ray diffraction and atom probe tomography. The analyses show that milling the starting powder for 10 h leads to the nanostructuration of the sample. The milled sample is partly oxidised and contains both non oxidised Mn60 +/- 5Al40 +/- 5 regions and oxidised regions. Annealing the powder for 1 h at 500 degrees C leads to enrichment in Al of the oxidised regions, and to the phase transformation of the non-oxidised regions into a nano-structured beta-Mn-like phase with a composition close to Mn3Al2. (C) 2013 Elsevier B. V. All rights reserved.

Towards ultra-high density magnetic recording

We have prepared Cu80Co20 powders by high-energy ball milling under ambient atmosphere. The evolutions of both the microstructure and the magnetic properties have been investigated as a function of milling time. 3D-focused ion beam was used for microstructural characterization for low milling time (1.5 h). For higher milling time (20 h) atom probe tomography was used to investigate at the atomic scale the elemental distribution of chemical species. In the first steps of milling, the powder presents a ferromagnetic signal due to the presence of micrometric cobalt particles. After 20 h of milling, the powder is composed of CoO particles with diameter around 10-50 nm surrounded by a copper rich matrix (Cu-84 +/- 2%, Co-16 +/- 2%) and a few cobalt-rich nanoclusters. For this milling time, a typical giant magnetoresistive effect is observed. A positive magnetoresistive effect is also observed at 5 K under low magnetic fields, which is related to the presence of Co oxides clusters. After a heat treatment at 450 degrees C for 1 h, the precipitation of Co into the copper rich matrix is observed, the enhanced, and the positive magnetoresistive effect disappears. giant magnetoresistive effect is enhanced, and the positive magnetoresistive effect disappears.

The tomographic atom probe (TAP) is a three-dimensional quantitative high-resolution microscope which provides, at the atomic scale, the spatial distribution of atoms in the analysed specimen. Until now, this technique was little used to characterize powder materials due the difficulties linked to atom probe specimen preparation. Nowadays, the development of new specimen preparation methods allows a systematic characterization of powder materials down to the atomic scale. In this paper, we report the results of TAP analyses of magnetoresistive Cu80Co20 granular alloys and nanocomposite SmCo5/α-Fe alloys.

Cu80Co20 granular alloy nanowires were synthesized by electrodeposition method and investigated by x-ray diffraction (XRD), Laser Assisted Wide Angle Tomographic Atom Probe (LAWATAP), and SQUID magnetometry. XRD results reveal the existence of a fcc Cu matrix and fcc Co-rich nanograins, with a preferred orientation along the [200] direction (perpendicular to the substrate surface). The Co-rich nanograins could be coherent with the Cu matrix. 3D reconstructions of a nano-sized volume, obtained by LAWATAP, reveal the heterogeneous aspect of the Cu80Co20 nanowires: Co-rich nanoclusters with size between 2 and 10 nm are detected, and the presence of Cu and Co oxides is evidenced. Magnetization measurements indicate that the Co-rich nanoclusters are superparamagnetic, with a blocking temperature that extends up to, at least, room temperature. The presence of ferromagnetic domains at room temperature indicates that some Co-rich nanoclusters are correlated within a volume that corresponds to a so-called interacting superparamagnetic phase. As a matter of fact, by LAWATAP atomic-scale analysis, a very good correlation is obtained between microstructure and magnetic properties.

We have synthesized strontium hexaferrite particles in an alkaline medium using a hydrothermal process at 180 degrees C. Our results show that to obtain a quasi-single SrFe12O19 phase, the Fe/Sr ratio in the initial solution must be equal to 8. However, the powders obtained contain traces of alpha-Fe2O3 and SrCO3. The SrFe12O19 hexaferrite particles are hexagonal-shaped platelets about 2 mu m wide and 40 nm thick. When heated to 1000 degrees C, SrCO3 reacts with SrFe12O19 to give Sr4Fe6O13. According to XRD analysis, Mossbauer spectrometry and magnetic measurements, the magnetization axis of the single-phase SrFe12O19 particle is perpendicular to the platelets. For an Fe/Sr ratio higher than 8, the alpha-Fe2O3 phase becomes the major phase and for a ratio lower than 8, the amount of SrCO3 increases. For an Fe/Sr ratio equal to 5, the formation of the Sr3Fe2(OH)(12) phase is also observed. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.