Irradiation-induced tailoring of the magnetism of CoFeB/MgO ultrathin films

Devolder, T.; Barisic, I.; Eimer, Sylvain; Garcia, K.; Adam, Jean-Paul; Ockert, B.; Ravelosona, D.

doi:10.1063/1.4808102

Cited by 46 publications

(37 citation statements)

References 31 publications

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“…11 A key feature to compare the performance of these films is their saturation magnetization Ms and its uniformity at the local scale. Conventional magnetometry methods like Superconducting Quantum Interference Device (SQUID) or vibrating sample magnetometers (VSMs) can inherently only give the spatial average of the magnetization and are prone to errors due to the parasitic magnetic signals coming from the substrate or the surface contamination.…”

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confidence: 99%

Measurement of magnetization using domain compressibility in CoFeB films with perpendicular anisotropy

Vernier¹,

Adam²,

Eimer³

et al. 2014

Applied Physics Letters

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Équipe 101 : Nanomagnétisme et électronique de spinInternational audienceWe present a method to map the saturation magnetization of soft ultrathin films with perpendicular anisotropy, and we illustrate it to assess the compositional dependence of the magnetization of CoFeB(1 nm)/MgO films. The method relies on the measurement of the dipolar repulsion of parallel domain walls that define a linear domain. The film magnetization is linked to the field compressibility of the domain. The method also yields the minimal distance between two walls before their merging, which sets a practical limit to the storage density in spintronic devices using domain walls as storage entities

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confidence: 99%

Measurement of magnetization using domain compressibility in CoFeB films with perpendicular anisotropy

Vernier¹,

Adam²,

Eimer³

et al. 2014

Applied Physics Letters

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“…4(a)]. This method enables precise tuning of PMA and magnetization through intermixing at both Ta|CoFeB and CoFeB|MgO interfaces, and can be adjusted by varying the irradiation dose [25,26]. A 1-µm-wide wire of Ta|CoFeB (1 nm)|MgO was irradiated through a mask with He + ions at 15 keV energy with a fluence of 1.6×10 15 ions/cm 2 [11].…”

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Measuring the Magnetic Moment Density in Patterned Ultrathin Ferromagnets with Submicrometer Resolution

et al. 2015

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We present a new approach to infer the surface density of magnetic moments Is in ultrathin ferromagnetic films with perpendicular anisotropy. It relies on quantitative stray field measurements with an atomic-size magnetometer based on the nitrogen-vacancy center in diamond. The method is applied to microstructures patterned in a 1-nm-thick film of CoFeB. We report measurements of Is with a few percent uncertainty and a spatial resolution in the range of (100 nm) 2 , an improvement by several orders of magnitude over existing methods. As an example of application, we measure the modifications of Is induced by local irradiation with He + ions in an ultrathin ferromagnetic wire. This method offers a new route to study variations of magnetic properties at the nanoscale.Ultrathin ferromagnetic films with perpendicular magnetic anisotropy (PMA) have attracted considerable interest over the last years both for fundamental studies in nanomagnetism and for the development of a new generation of low power spintronic devices [1][2][3]. In this context, it is crucial to determine accurately the surface density of magnetic moments I s in such ultrathin ferromagnets, which can not be simply inferred from tabulated bulk values owing to significant interface effects [4]. To this end, macroscopic magnetometry methods like superconducting quantum interference devices (SQUIDs) or vibrating-sample magnetometers have become ubiquitous owing to simplicity of use. However, these conventional techniques are prone to parasitic magnetic signals, leading to an intrinsic background on the order of 10 . To overcome this background, the ferromagnetic signal needs to be averaged over a large sample, thus limiting drastically the spatial resolution of the measurement. As an example, we consider a ferromagnetic film with a typical thickness t = 1 nm and a saturation magnetization of M s = 10 6 A/m, corresponding to a surface density of magnetic moments I s = M s t ≈ 100 µ B /nm 2 . In order to reach a signal-to-background ratio of ∼ 10, the signal must be averaged over a surface larger than (1 mm) 2 . Different approaches have been used to tackle this issue. Notably, a recent improvement of the spatial resolution down to the order of (10 µm) 2 has been achieved by measuring the dipolar repulsion of magnetic domain walls with a magneto-optical Kerr microscope [9]. The use of micro-and even nano-SQUID also allows for a significant gain in sensitivity and resolution. However it remains difficult with such devices to determine accurately the link between magnetic flux and magnetization, and thus to extract precise values of I s [10].In this work, we use a single nitrogen-vacancy (NV) center in diamond as an atomic-size magnetometer to probe the stray field above ultrathin ferromagnets and infer I s on a scale smaller than (100 nm) 6 A/m and t = 1 nm, corresponding to Is = Mst ≈ 100 µB/nm 2 , which is a typical value for the ferromagnetic samples considered in this work. The edge is placed at x = 0. out applying any external magnetic field, which en...

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“…As a result, CoFeB alloys are usually chosen, 3-5 because they have the relevant properties. 6,7 However intermetallics with greater exchange stiffness and Curie temperature, together with lower magnetization M s and lower damping are desirable. This is first to fully benefit from the interface anisotropy without paying the destabilization cost of the perpendicular demagnetizing field and second, to favor coherent magnetization reversal compared to domain wall mediated reversal.…”

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Compositional dependence of the magnetic properties of epitaxial FeV/MgO thin films

Devolder¹,

Tahmasebi²,

Eimer³

et al. 2013

Applied Physics Letters

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International audienceOwing to their bcc structures and the low lattice misfit with MgO, FeV alloys are interesting for MgO-based magnetic tunnel junctions. We use vector network analyzer ferromagnetic resonance to measure the magnetization, anisotropy, exchange stiffness, and damping of epitaxial FeV/MgO thin alloys of various V contents. The low magnetization, very high exchange stiffness (23 pJ/m) and very low effective damping (<0.0026) of the alloy with 20% V content makes it an interesting candidate for spin torque applications. The ultralow damping is consistent with a spin-orbit origin, which sheds light on the possible strategies to reduce the damping in alloys

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Irradiation-induced tailoring of the magnetism of CoFeB/MgO ultrathin films

Cited by 46 publications

References 31 publications

Measurement of magnetization using domain compressibility in CoFeB films with perpendicular anisotropy

Measurement of magnetization using domain compressibility in CoFeB films with perpendicular anisotropy

Measuring the Magnetic Moment Density in Patterned Ultrathin Ferromagnets with Submicrometer Resolution

Compositional dependence of the magnetic properties of epitaxial FeV/MgO thin films

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