arXiv subjects

V. Baltz

Publications and source records attributed to V. Baltz.

17 recordsLinked to original sources

arXiv2025

Dissipation properties of anomalous Hall effect: intrinsic vs. extrinsic magnetic materials

A comparative study of anomalous-Hall current injection and anisotropic current injection (through planar Hall effect) are studied in Hall devices contacted to a lateral load circuit. Hall currents are injected into the load circuit from three different kinds of magnetic Hall bars: Mn5Si3 altermagnet, Co75Gd25 ferrimagnet, and Ni80Fe20 ferromagnet. The current, the voltage and the power are measured as a function of the load resistance and the Hall angle. It is observed that the power dissipated for the three kinds of materials fellow the same law as a function of load resistance and Hall angle, at the leading order in the Hall angle. Since the anomalous Hall effect in the altermagnetic Hall-bar is due to the intrinsic topological structure (i.e. due to the presence of a Berry phase in the reciprocal space), these observations suggest that the dissipative properties of anomalous Hall effect are dominated by the injection of electric charges accumulated at the edges (including electric screening), instead of the very mechanism responsible for it.

cond-mat.mes-hall↗

arXiv2021

Anisotropic long-range spin transport in canted antiferromagnetic orthoferrite YFeO$_3$

In antiferromagnets, the efficient propagation of spin-waves has until now only been observed in the insulating antiferromagnet hematite, where circularly (or a superposition of pairs of linearly) polarized spin-waves propagate over long distances. Here, we report long-distance spin-transport in the antiferromagnetic orthoferrite YFeO$_3$, where a different transport mechanism is enabled by the combined presence of the Dzyaloshinskii-Moriya interaction and externally applied fields. The magnon decay length is shown to exceed hundreds of nano-meters, in line with resonance measurements that highlight the low magnetic damping. We observe a strong anisotropy in the magnon decay lengths that we can attribute to the role of the magnon group velocity in the propagation of spin-waves in antiferromagnets. This unique mode of transport identified in YFeO$_3$ opens up the possibility of a large and technologically relevant class of materials, i.e., canted antiferromagnets, for long-distance spin transport.

cond-mat.str-el↗

arXiv2021

Penetration depth of Cooper pairs in the IrMn antiferromagnet

Suppression of superconductivity due to the proximity effect between a superconductor and a ferromagnet can be partially alleviated when a Cooper pair simultaneously samples different directions of the short-range exchange field. The superconductor's critical temperature, TC, is therefore expected to partially recover when the ferromagnet is in a multi-domain state, as opposed to a single-domain state. Here, we discuss series of experiments performed with ferromagnet(Pt/Co)/spacer(IrMn and Pt)/superconductor(NbN) heterostructures. By tuning the various parameters in play, e.g., superconducting coherence length-to-thicknesses ratio, and domain sizes, we obtained up to 10 percent recovery of the superconducting critical temperature ΔTC/TC. This large-scale recovery made novel investigations possible. In particular, from the spacer thickness-dependence of ΔTC/TC, it was possible to deduce the characteristic length for Cooper pair penetration in an IrMn antiferromagnet. This information is crucial for electronic transport, and up to now has been difficult to access experimentally for antiferromagnets.

cond-mat.mtrl-sci↗

arXiv2019

Self-induced inverse spin Hall effect in ferromagnets: demonstration through non-monotonous temperature-dependence in permalloy

We investigated the self-induced inverse spin Hall effect in ferromagnets. Temperature (T), thickness (t) and angular-dependent measurements of transverse voltage in spin pumping experiments were performed with permalloy films. Results revealed non-monotonous T-dependence of the self-induced transverse voltage. Qualitative agreement was found with first-principle calculations unravelling the skew scattering, side-jump, and intrinsic contributions to the T-dependent spin Hall conductivity. Experimental data were similar whatever the material in contact with permalloy (oxides or metals), and revealed an increase of produced current with t, demonstrating a bulk origin of the effect.

cond-mat.mes-hall↗

arXiv2019

Stacking order-dependent sign-change of microwave phase due to eddy currents in nanometer-scale NiFe/Cu heterostructures

In the field of spintronics, ferromagnetic/non-magnetic metallic multilayers are core building blocks for emerging technologies. Resonance experiments using stripline transducers are commonly used to characterize and engineer these stacks for applications. Up to now in these experiments, the influence of eddy currents on the excitation of the dynamics of ferromagnetic magnetization below the skin-depth limit was most often neglected. Here, using a coplanar stripline transducer, we experimentally investigated the broadband ferromagnetic resonance response of NiFe/Cu bilayers a few nanometers thick in the sub-skin-depth regime. Asymmetry in the absorption spectrum gradually built up as the excitation frequency and Cu-layer thickness increased. Most significantly, the sign of the asymmetry depended on the stacking order. Experimental data were consistent with a quantitative analysis considering eddy currents generated in the Cu layers and the subsequent phaseshift of the feedback magnetic field generated by the eddy currents. These results extend our understanding of the impact of eddy currents below the microwave magnetic skin-depth and explain the lineshape asymmetry and phase lags reported in stripline experiments.

cond-mat.mes-hall↗

arXiv2019

Spin pumping as a generic probe for linear spin fluctuations: demonstration with ferromagnetic and antiferromagnetic orders, metallic and insulating electrical states

We investigated spin injection by spin pumping from a spin-injector(NiFe) into a spin-sink to detect spin fluctuations in the spin-sink. By scanning the ordering-temperature of several magnetic transitions, we found that enhanced spin pumping due to spin fluctuations applies with several ordering states: ferromagnetic(Tb) and antiferromagnetic(NiO, NiFeOx, BiFeO3, exchange-biased and unbiased IrMn). Results also represent systematic experimental investigation supporting that the effect is independent of the metallic and insulating nature of the spin-sink, and is observed whether the spin current probe involves electronic or magnonic transport, facilitating advances in material characterization and engineering for spintronic applications.

cond-mat.mtrl-sci↗

arXiv2018

Unraveling the influence of electronic and magnonic spin current injection near the magnetic ordering transition of IrMn metallic antiferromagnets

Although spin injection at room temperature in an IrMn metallic antiferromagnet strongly depends on the transport regime, and is more efficient in the case of magnonic transport, in this article, we present experimental data demonstrating that the enhanced efficiency of spin injection caused by spin fluctuations near the ordering temperature can be as efficient for the electronic and magnonic transport regimes. By selecting representative interacting environments, we also demonstrated that the amplification of spin injection near the ordering temperature of the IrMn antiferromagnet is independent of exchange coupling with an adjacent NiFe ferromagnet. In addition, our findings confirm that the spin current carried by magnons penetrates deeper than that transported by conduction electrons in IrMn. Finally, our data indicates that the value of the ordering temperature for the IrMn antiferromagnet is not significantly affected by either the electronic or magnonic nature of the spin current probe, or by exchange coupling.

cond-mat.mtrl-sci↗

arXiv2017

Antiferromagnetic spintronics

Antiferromagnetic materials could represent the future of spintronic applications thanks to the numerous interesting features they combine: they are robust against perturbation due to magnetic fields, produce no stray fields, display ultrafast dynamics and are capable of generating large magneto-transport effects. Intense research efforts over the past decade have been invested in unraveling spin transport properties in antiferromagnetic materials. Whether spin transport can be used to drive the antiferromagnetic order and how subsequent variations can be detected are some of the thrilling challenges currently being addressed. Antiferromagnetic spintronics started out with studies on spin transfer, and has undergone a definite revival in the last few years with the publication of pioneering articles on the use of spin-orbit interactions in antiferromagnets. This paradigm shift offers possibilities for radically new concepts for spin manipulation in electronics. Central to these endeavors are the need for predictive models, relevant disruptive materials and new experimental designs. This paper reviews the most prominent spintronic effects described based on theoretical and experimental analysis of antiferromagnetic materials. It also details some of the remaining bottlenecks and suggests possible avenues for future research.

cond-mat.mtrl-sci↗

arXiv2016

Relaxation mechanism driven by spin angular momentum absorption throughout antiferromagnetic phase transition in NiFe surface oxides

We report an alternative mechanism for the physical origin of the temperature-dependent ferromagnetic relaxation of Permalloy (NiFe) thin films. Through spin-pumping experiments, we demonstrate that the peak in the temperature-dependence of NiFe damping can be understood in terms of enhanced spin angular momentum absorption at the magnetic phase transition in antiferromagnetic surface-oxidized layers. These results suggest new avenues for the investigation of an incompletely-understood phenomenon in physics.

cond-mat.mtrl-sci↗

arXiv2013

Spatially periodic domain wall pinning potentials: Asymmetric pinning and dipolar biasing

Domain wall propagation has been measured in continuous, weakly disordered, quasi-two-dimensional, Ising-like magnetic layers that are subject to spatially periodic domain wall pinning potentials. The potentials are generated non-destructively using the stray magnetic field of ordered arrays of magnetically hard [Co/Pt]$_m$ nanoplatelets which are patterned above and are physically separated from the continuous magnetic layer. The effect of the periodic pinning potentials on thermally activated domain wall creep dynamics is shown to be equivalent, at first approximation, to that of a uniform, effective retardation field, $H_{ret}$, which acts against the applied field, $H$. We show that $H_{ret}$ depends not only on the array geometry but also on the relative orientation of $H$ and the magnetization of the nanoplatelets. A result of the latter dependence is that wall-mediated hysteresis loops obtained for a set nanoplatelet magnetization exhibit many properties that are normally associated with ferromagnet/antiferromagnet exchange bias systems. These include a switchable bias, coercivity enhancement and domain wall roughness that is dependent on the applied field polarity.

cond-mat.mes-hall↗

arXiv2013

Crossover from spin accumulation into interface states to spin injection in the germanium conduction band

Electrical spin injection into semiconductors paves the way for exploring new phenomena in the area of spin physics and new generations of spintronic devices. However the exact role of interface states in spin injection mechanism from a magnetic tunnel junction into a semiconductor is still under debate. In this letter, we demonstrate a clear transition from spin accumulation into interface states to spin injection in the conduction band of $n$-Ge. We observe spin signal amplification at low temperature due to spin accumulation into interface states followed by a clear transition towards spin injection in the conduction band from 200 K up to room temperature. In this regime, the spin signal is reduced down to a value compatible with spin diffusion model. More interestingly, we demonstrate in this regime a significant modulation of the spin signal by spin pumping generated by ferromagnetic resonance and also by applying a back-gate voltage which are clear manifestations of spin current and accumulation in the germanium conduction band.

cond-mat.mtrl-sci↗

arXiv2012

Electrical and thermal spin accumulation in germanium

In this letter, we first show electrical spin injection in the germanium conduction band at room temperature and modulate the spin signal by applying a gate voltage to the channel. The corresponding signal modulation agrees well with the predictions of spin diffusion models. Then by setting a temperature gradient between germanium and the ferromagnet, we create a thermal spin accumulation in germanium without any tunnel charge current. We show that temperature gradients yield larger spin accumulations than pure electrical spin injection but, due to competing microscopic effects, the thermal spin accumulation in germanium remains surprisingly almost unchanged under the application of a gate voltage to the channel.

cond-mat.mtrl-sci↗

arXiv2011

Electrical spin injection and detection in Germanium using three terminal geometry

In this letter, we report on successful electrical spin injection and detection in \textit{n}-type germanium-on-insulator (GOI) using a Co/Py/Al$_{2}$O$_{3}$ spin injector and 3-terminal non-local measurements. We observe an enhanced spin accumulation signal of the order of 1 meV consistent with the sequential tunneling process via interface states in the vicinity of the Al$_{2}$O$_{3}$/Ge interface. This spin signal is further observable up to 220 K. Moreover, the presence of a strong \textit{inverted} Hanle effect points at the influence of random fields arising from interface roughness on the injected spins.

cond-mat.mtrl-sci↗

arXiv2010

Dynamic binding of driven interfaces in coupled ultrathin ferromagnetic layers

We demonstrate experimentally dynamic interface binding in a system consisting of two coupled ferromagnetic layers. While domain walls in each layer have different velocity-field responses, for two broad ranges of the driving field, H, walls in the two layers are bound and move at a common velocity. The bound states have their own velocity-field response and arise when the isolated wall velocities in each layer are close, a condition which always occurs as H->0. Several features of the bound states are reproduced using a one dimensional model, illustrating their general nature.

cond-mat.mtrl-sci↗

arXiv2007

Creep and flow regimes of magnetic domain wall motion in ultrathin Pt/Co/Pt films with perpendicular anisotropy

We report on magnetic domain wall velocity measurements in ultrathin Pt/Co(0.5-0.8 nm)/Pt films with perpendicular anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domain wall motion, analysis of which yields values for the damping parameter, $α$.

cond-mat.mtrl-sci↗

arXiv2007

Diffusive and ballistic current spin-polarization in magnetron-sputtered L1o-ordered epitaxial FePt

We report on the structural, magnetic, and electron transport properties of a L1o-ordered epitaxial iron-platinum alloy layer fabricated by magnetron-sputtering on a MgO(001) substrate. The film studied displayed a long range chemical order parameter of S~0.90, and hence has a very strong perpendicular magnetic anisotropy. In the diffusive electron transport regime, for temperatures ranging from 2 K to 258 K, we found hysteresis in the magnetoresistance mainly due to electron scattering from magnetic domain walls. At 2 K, we observed an overall domain wall magnetoresistance of about 0.5 %. By evaluating the spin current asymmetry alpha = sigma_up / sigma_down, we were able to estimate the diffusive spin current polarization. At all temperatures ranging from 2 K to 258 K, we found a diffusive spin current polarization of > 80%. To study the ballistic transport regime, we have performed point-contact Andreev-reflection measurements at 4.2 K. We obtained a value for the ballistic current spin polarization of ~42% (which compares very well with that of a polycrystalline thin film of elemental Fe). We attribute the discrepancy to a difference in the characteristic scattering times for oppositely spin-polarized electrons, such scattering times influencing the diffusive but not the ballistic current spin polarization.

cond-mat.mtrl-sci↗

arXiv2006

Magnetic domain structure and dynamics in interacting ferromagnetic stacks with perpendicular anisotropy

The time and field dependence of the magnetic domain structure at magnetization reversal were investigated by Kerr microscopy in interacting ferromagnetic Co/Pt multilayers with perpendicular anisotropy. Large local inhomogeneous magnetostatic fields favor mirroring domain structures and domain decoration by rings of opposite magnetization. The long range nature of these magnetostatic interactions gives rise to ultra-slow dynamics even in zero applied field, i.e. it affects the long time domain stability. Due to this additionnal interaction field, the magnetization reversal under short magnetic field pulses differs markedly from the well-known slow dynamic behavior. Namely, in high field, the magnetization of the coupled harder layer has been observed to reverse more rapidly by domain wall motion than the softer layer alone.

cond-mat.mtrl-sci↗