Voltage‐Induced Coercivity Reduction in Nanoporous Alloy Films: A Boost toward Energy‐Efficient Magnetic Actuation

Quintana, Alberto; Zhang, Jin; Isarain‐Chávez, Eloy; Menéndez, Enric; Cuadrado, R.; Robles, Roberto; Baró, María Dolors; Guerrero, Miguel; Pané, Salvador; Nelson, Bradley J.; Müller, C.; Ordejón, Pablo; Nogués, J.; Pellicer, Eva; Sort, Jordi

doi:10.1002/adfm.201701904

Cited by 44 publications

(86 citation statements)

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“…[26,27]. The family of L1 0 alloys considered in this work is also versatile, since their structure and magnetic properties can be tailored by varying the stoichiometry, as it is the case of the strongly magnetostrictive 'galfenol' (Fe 1−x Ga x ) [28,29], Fe 1−x Co x [30][31][32], and Cu-Ni films [33]. Several theoretical studies have shown that a bias voltage could significantly affect the MCA [34,35] and, in fact, an electric-field-induced MCA switching has been realized in Fe 30 Co 70 alloy films [36].…”

Section: Introductionmentioning

confidence: 99%

Validity of perturbative methods to treat the spin–orbit interaction: application to magnetocrystalline anisotropy

2019

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A second-order perturbation (2PT) approach to the spin-orbit interaction (SOI) is implemented within a density-functional theory framework. Its performance is examined by applying it to the calculation of the magnetocrystalline anisotropy energies (MAE) of benchmark systems, and its efficiency and accuracy are compared with the popular force theorem method. The case studies are tetragonal FeMe alloys (Me=Co, Cu, Pd, Pt, Au), as well as FeMe (Me=Co, Pt) bilayers with (111) and (100) symmetry, which cover a wide range of SOI strength and electronic band structures. The 2PT approach is found to provide a very accurate description for 3d and 4d metals and, moreover, this methodology is robust enough to predict easy axis switching under doping conditions. In all cases, the details of the bandstructure, including states far from the Fermi level, are responsible for the finally observed MAE value, sometimes overruling the effect of the SOI strength. From a technical point of view, it is confirmed that accuracy in the MAE calculations is subject to the accuracy of the Fermi level determination.The interplay of MCA and dimensionality is considered as a promising route for the development of spintronics. Furthermore, MCA plays a central role in the magnetic properties of two-dimensional materials, since it can prevent thermal fluctuations from destroying long-range magnetic order [8]. In this context, density functional theory (DFT) calculations that include SOI constitute a powerful theoretical tool to characterize the MCA. Nonetheless, the small magnitude of the associated magnetocrystalline anisotropy energy (MAE) imposes stringent convergence to the DFT calculations at the expense of high computational demands. In practice, fully relativistic DFT calculations that include SOI are carried out by first computing self-consistently the Hamiltonian of the system including the scalar relativistic term and next adding the spin-orbit contribution. The latter may be treated self-consistently (FSC) or non-self-consistently [9, 10] within the so-called force theorem (FT) [11] to obtain the MAE. FT is often considered to produce a good estimate of the FSC MAE value for every system, at least for bulk crystals, although it has been shown to be less accurate in the case of low dimensional systems [12]. In any case, this comparison between FT and SCF calculations can only be done for relatively simple systems, because the FSC tends to be computationally too demanding. Alternatively, Green's function methods that treat SOI at the level of second-order perturbation theory (2PT) have been formulated in the literature under different flavours [13][14][15][16][17]. These approaches rely on the knowledge of the spin-orbit effects on atomic orbitals (AOs) [18][19][20], which can be quasi-analytically accounted. However, to our knowledge, the versatility of those perturbative methods has not been exploited within a DFT environment. Considering the high computational expense involved in DFT calculations that include SOI under the aforemention...

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Section: Introductionmentioning

confidence: 99%

Validity of perturbative methods to treat the spin–orbit interaction: application to magnetocrystalline anisotropy

2019

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“…From a technological viewpoint, a reproducible, strong, and tunable magnetoelectric effect is required in a solid-state device configuration. So far, in contrast to single-phase multiferroics (with intrinsic magnetoelectric coupling) [4][5][6] and direct field effects (charge-mediated mechanism) in ultrathin metals and nanoporous alloys [7][8][9][10], the strain-mediated converse magnetoelectric the FM induced by the piezoelectric strain arising from the FE, charge accumulation at the surface of the FM (typically only observed for thicknesses of a few nm) [7][8][9][10], and voltage-driven oxygen migration may simultaneously occur. This makes interpretation of the observed effects not straightforward, leading to misinterpretations.…”

Section: Introductionmentioning

confidence: 99%

Disentangling Highly Asymmetric Magnetoelectric Effects in Engineered Multiferroic Heterostructures

et al. 2019

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One of the main strategies to control magnetism by voltage is the use of magnetostrictive-piezoelectric hybrid materials, such as ferromagnetic-ferroelectric heterostructures. When such heterostructures are subjected to an electric field, piezostrain-mediated effects, electronic charging, and voltage-driven oxygen migration (magnetoionics) may simultaneously occur, making the interpretation of the magnetoelectric effects not straightforward and often leading to misconceptions. Typically, the strain-mediated magnetoelectric response is symmetric with respect to the sign of the applied voltage because the induced strain (and variations in the magnetization) depends on the square of the ferroelectric polarization. Conversely, asymmetric responses can be obtained from electronic charging and voltage-driven oxygen migration. By engineering a ferromagnetic-ferroelectric hybrid consisting of a magnetically soft 50-nm thick Fe 75 Al 25 (at. %) thin film on top of a 110-oriented Pb(Mg 1/3 Nb 2/3)O 3-32PbTiO 3 ferroelectric crystal, a highly asymmetric magnetoelectric response is obtained and the aforementioned magnetoelectric effects can be disentangled. Specifically, the large thickness of the Fe 75 Al 25 layer allows dismissing any possible charge accumulation effect, whereas no evidence of magnetoionics is observed experimentally, as expected from the high resistance to oxidation of Fe 75 Al 25 , leaving strain as the only mechanism to modulate the asymmetric magnetoelectric response. The origin of this asymmetric strain-induced magnetoelectric effect arises from the asymmetry of the polarization reversal in the particular crystallographic orientation of the ferroelectric substrate. These results are important to optimize the performance of artificial multiferroic heterostructures.

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“…In order to perform in situ magnetic measurements, a home‐made cell setup was employed . Voltage was applied between the nanoporous CuNi film and a platinum wire.…”

Section: Methodsmentioning

confidence: 99%

“…All these phenomena are interface‐driven and, consequently, are expected to be maximized in materials with a high surface area‐to‐volume ratio, a parameter which is largely exploited in a widespread range of applications . Although this is typically achieved in ultrathin films, nanoporous magnetic alloys, with extremely large surface area‐to‐volume ratios, may be an appealing alternative . However, so far, the magnetoelectric effects in nanoporous materials have been rather overlooked.…”

Section: Introductionmentioning

confidence: 99%

Tunable Magnetism in Nanoporous CuNi Alloys by Reversible Voltage‐Driven Element‐Selective Redox Processes

Quintana

Menéndez

Isarain‐Chávez

et al. 2018

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Voltage-driven manipulation of magnetism in electrodeposited 200 nm thick nanoporous single-phase solid solution Cu Ni (at%) alloy films (with sub 10 nm pore size) is accomplished by controlled reduction-oxidation (i.e., redox) processes in a protic solvent, namely 1 m NaOH aqueous solution. Owing to the selectivity of the electrochemical processes, the oxidation of the CuNi film mainly occurs on the Cu counterpart of the solid solution, resulting in a Ni-enriched alloy. As a consequence, the magnetic moment at saturation significantly increases (up to 33% enhancement with respect to the as-prepared sample), while only slight changes in coercivity are observed. Conversely, the reduction process brings Cu back to its metallic state and, remarkably, it becomes alloyed to Ni again. The reported phenomenon is fully reversible, thus allowing for the precise adjustment of the magnetic properties of this system through the sign and amplitude of the applied voltage.

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Voltage‐Induced Coercivity Reduction in Nanoporous Alloy Films: A Boost toward Energy‐Efficient Magnetic Actuation

Cited by 44 publications

References 48 publications

Validity of perturbative methods to treat the spin–orbit interaction: application to magnetocrystalline anisotropy

Validity of perturbative methods to treat the spin–orbit interaction: application to magnetocrystalline anisotropy

Disentangling Highly Asymmetric Magnetoelectric Effects in Engineered Multiferroic Heterostructures

Tunable Magnetism in Nanoporous CuNi Alloys by Reversible Voltage‐Driven Element‐Selective Redox Processes

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