Room Temperature In-plane <100> Magnetic Easy Axis for Fe3O4/SrTiO3(001):Nb Grown by Infrared PLD

We examine the magnetic easy-axis directions of stoichiometric magnetite films grown on SrTiO3:Nb by infrared pulsed-laser deposition. Spin-polarized low-energy electron microscopy reveals that the individual magnetic domains are magnetized along the in-plane film directions. Magneto-optical Kerr effect measurements show that the maxima of the remanence and coercivity are also along in-plane film directions. This easy-axis orientation differs from bulk magnetite and films prepared by other techniques, establishing that the magnetic anisotropy can be tuned by film growth.Comment: 3 pages, 3 figure

Emergence of the Stoner-Wohlfarth astroid in thin films at dynamic regime

The Stoner-Wohlfarth (SW) model is the simplest model that describes adequately the magnetization reversal of nanoscale systems that are small enough to contain single magnetic domains. However for larger sizes where multi-domain effects are present, e.g., in thin films, this simple macrospin approximation fails and the experimental critical curve, referred as SW astroid, is far from its predictions. Here we show that this discrepancy could vanish also in extended system. We present a detailed angular-dependent study of magnetization reversal dynamics of a thin film with well-defined uniaxial magnetic anisotropy, performed over 9 decades of applied field sweep rate (dH/dt). The angular-dependent properties display a gradual transition from domain wall pinning and motion-like behaviour to a nucleative single-particle one, as dH/dt increases. Remarkably, in the high dynamic regime, where nucleation of reversed domains is the dominant mechanism of the magnetization reversal (nucleative regime), the magnetic properties including the astroid become closer to the ones predicted by SW model. The results also show why the SW model can successfully describe other extended systems that present nucleative regime, even in quasi-static conditionsThis work has been supported by MINECO (Ministerio de Economía y Competitividad) through Projects No. MAT2012-39308, FIS2015-67287-P, and FIS2016-78591-C3-1-R, by the Comunidad de Madrid through Project S2013/MIT-2850 NANOFRONTMAG-CM, and by MINECO through the FLAGERA Programme of Graphene Flagship: SOgraph project (No. PCIN-2015-216); and M-era.Net Programme: NEXMAG project (PCIN- 2015-126). IMDEA-Nanociencia acknowledges support from the ‘Severo Ochoa’ Program for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686). P.P. acknowledges support through the Marie Curie AMAROUT EU Programme and JCI-2011-09602. A.B. acknowledges MINECO through the ENMA-National project (MAT2014-56955-R)

An extraordinary chiral exchange-bias phenomenon: Engineering the sign of the bias field in orthogonal bilayers by a magnetically switchable response mechanism

[EN] Isothermal tuning of both the magnitude and the sign of the bias field has been achieved by exploiting a new phenomenon in a system consisting of two orthogonally coupled films: SmCo (out-of-plane anisotropy)-CoFeB (in-plane anisotropy). This has been achieved by using the large dipolar magnetic field of the SmCo layer resulting in the pinning of one of the branches of the hysteresis loop (either the ascending or the descending branch) at a fixed field value while the second one is modulated along the field axis by varying the orientation of an externally applied magnetic field. This means the possibility of controlling the sign of the bias field in a manner not reported to date. Moreover, modulation of the bias field strength is possible by varying the thickness of a spacer between the SmCo and CoFeB layers. This study shows that the observed phenomena find their origin in the competition between the artificially induced anisotropies in both layers, resulting in a reversible chiral bias effect that allows the selection of the initial sign of the bias field by switching (upwards/downwards) the magnetization in the SmCo film.This research was supported by the Joint German-Spanish Actions Programme (DAAD and Fundación Universidad.es via Ref. 57050243), the Spanish Ministerio de Economía y Competitividad (MINECO) through “SIESPER” (MAT2011-25598) Project, and the Regional Government of Madrid through NANOMAGCOST (P2018/NMT-4321) project. D. S. acknowledges financial support from Xunta de Galicia under the postdoctoral program I2C Plan (Modalidade B) and the Strategic Grouping in Materials (AeMAT; grant No.ED431E2018/08). IMDEA Nanoscience is supported by the ‘Severo Ochoa’ Programme for Centres of Excellence in R&D, MINECO [grant number SEV-2016-0686]Electronic supplementary information (ESI) available. See DOI: 10.1039/c9nr08852

Erratun: G-force induced giant efficiency of nanoparticles internalization into living cells

The original version of this Article contained a typographical error in the spelling of the author Jose Luis F. Cuñado, which was incorrectly given as Jose Luis, F. Cuñad

Interfacial Exchange Phenomena Driven by Ferromagnetic Domains

Interfacial proximity effects in antiferromagnetic/ferromagnetic (AFM/FM) bilayers control the exchange-bias (EB) phenomena exploited in most spintronic devices, although still is lack of full understanding. Discordant results, including different exchange-bias field (HE), coercivity (HC), or blocking temperature (TB) found even in similar systems, are usually ascribed to uncontrolled parameters, namely dissimilar interfacial defects, structure, and thicknesses. Here, it is shown in the very same sample that the magnetic domain structure during the magnetization reversal of the FM layer controls those mentioned effects. Simultaneous transport and vectorial-resolved magnetic measurements performed in a V2O3/Co system during warming after different field cooling (FC) procedures exhibit a strong dependence on the FC angle and the domain structure of the FM layer. Remarkably, magnetization reversal analysis reveals 35 K of variation in TB and up to a factor of two in HE. These observations can be explained within the random-field model for the interfacial exchange coupling with a fixed AFM domain structure in contact with a variable (angle-dependent) FM domain structure. The results highlight the importance of the domain structure and magnetization reversal of the FM layer (not previously considered) in the EB phenomena, with potential to tailor interfacial effects in future spintronic devicesThis is a highly collaborative effort between IMDEA Nanociencia and UC San Diego. The authors thank C. Urban for help in the initial stages of this work. The sample fabrication and characterization were supported by the Department of Energy’s Office of Basic Energy Science, under grant # DE-FG02-87ER45332. The magnetic and transport measurements were supported by MINECO (Ministerio de Economía y Competitividad) (FIS2016-78591-C3-1-R, PGC2018-098613-B-C21, MAT2017-89960-R, RTI2018-097895-B-C42, PCI2019-111867-2, PID2020-116181RB-C31) and by Comunidad de Madrid Regional Government (NanomagCOST-CM, Ref. S2018/MIT-2850). J.M.D. acknowledges support from MINECO through the FPI program (BES-2017-080617). IMDEA-Nanociencia acknowledges support from the ‘Severo Ochoa’ Program for Centres of Excellence in R&D (MINECO Grants SEV-2016-0686, CEX2020-001039-S

An extraordinary chiral exchange-bias phenomenon: engineering the sign of the bias field in orthogonal bilayers by a magnetically switchable response mechanism

International audienceIsothermal tuning of both the magnitude and the sign of the bias field has been achieved by exploiting a new phenomenon in a system consisting of two orthogonally coupled films: SmCo5 (out-of-plane anisotropy)-CoFeB (in-plane anisotropy). This has been managed by using the large dipolar magnetic field of the SmCo5 layer resulting in pinning one of the branches of the hysteresis loop (either the ascending or the descending branch) at a fixed field value while the second one is modulated along the field axis by varying the orientation of an externally applied magnetic field. This means the possibility of controlling the sign of the bias field in a manner not reported to date. Moreover, modulation of the bias field strength is possible by varying the thickness of a spacer between the SmCo5 and CoFeB layers. This study shows that the observed phenomena find their origin in the competition of artificially induced anisotropies on both layers, resulting in a reversible chiral bias effect that allows selecting the initial sign of the bias field by switching (upwards/downwards) the magnetization in the SmCo5 film