arXiv subjects

J. Godinho

Publications and source records attributed to J. Godinho.

5 recordsLinked to original sources

arXiv2026

Spin-orbit torque-driven synthetic antiferromagnetic oscillator

Antiferromagnets offer a promising route toward robust spintronic devices because of their compensated magnetic order and exchange-enhanced spin dynamics. Here, we demonstrate a spin-orbit torque (SOT)-driven antiferromagnetic oscillator based on a nanoconstriction patterned from a synthetic antiferromagnet (SAF). Spin-rectification spectroscopy reveals electrical excitation of both acoustic and optical SAF eigenmodes, whose field and frequency dependences are quantitatively described by an antiferromagnetic resonance model. In addition to these linear eigenmodes, we observe low-field spin-rectification peaks that emerge only above a threshold DC current near the spin-flop transition. Their current-polarity-dependent sign and locking to an injected RF frequency provide electrical spin-rectification signatures consistent with current-selected chiral self-oscillatory dynamics. Micromagnetic simulations reproduce the threshold excitation of SOT-driven self-oscillations and injection locking, while macrospin simulations predict stable and chaotic nonlinear dynamics within the same spin-flop region. We interpret the multi-peak, weakly RF-frequency-dependent responses as a qualitative signature of complex nonlinear dynamics. These results establish SAF nanoconstrictions as an experimentally accessible platform for studying current-driven antiferromagnetic-like oscillator dynamics and motivate future work on nonlinear spintronic devices for signal processing and reservoir-computing concepts.

cond-mat.mes-hall↗

arXiv2026

Sign-resolved nanoscale readout and control of hidden antiferromagnetic spin order

Antiferromagnetic memories promise ultrafast, stray-field-free information storage. Yet perfect magnetic compensation conceals the information carrier itself: the sign of the N\'eel vector distinguishing two time-reversed states. Moreover, in future dense memories, the local polarity of N\'eel domains would need to be read out on the nanoscale. We make this hidden polarity visible in a fully-compensated, high-N\'eel-temperature, PT-symmetric antiferromagnet by driving interband electric-dipole transitions by mid-infrared near-fields confined at a scanning probe. The excitation generates a N\'eel-order-dependent quantum-metric photocurrent, a Hall-like signal reversing with N\'eel order, which we term the optical nonlinear anomalous Hall effect. This optically induced electrical readout maps opposite N\'eel polarities with sub-100-nm resolution at room temperature and, combined with spin-orbit-torque writing, reveals N\'eel-texture polarization and reversible domain-wall motion, establishing electrical-write/optoelectronic-read antiferromagnetic functionality.

cond-mat.mtrl-sci↗

arXiv2022

Identifying the octupole Antiferromagnetic domain orientation in Mn$_{3}$NiN by scanning Anomalous Nernst Effect microscopy

The intrinsic anomalous Nernst effect in a magnetic material is governed by the Berry curvature at the Fermi energy and can be realized in non-collinear antiferromagnets with vanishing magnetization. Thin films of (001)-oriented Mn$_{3}$NiN have their chiral antiferromagnetic structure located in the (111) plane facilitating the anomalous Nernst effect unusually in two orthogonal in-plane directions. The sign of each component of the anomalous Nernst effect is determined by the local antiferromagnetic domain state. In this work, a temperature gradient is induced in a 50 nm thick Mn$_{3}$NiN two micron-size Hall cross by a focused scanning laser beam, and the spatial distribution of the anomalous Nernst voltage is used to image and identify the octupole macrodomain arrangement. Although the focused laser beam width may span many individual domains, cooling from room temperature through the antiferromagnetic transition temperature in an in-plane magnetic field prepares the domain state producing a checkerboard pattern resulting from the convolution of contributions from each domain. These images together with atomistic and micromagnetic simulations suggest an average macrodomain of the order of $1 μm^{2}$.

cond-mat.str-el↗

arXiv2018

Magnetic anisotropy in antiferromagnetic hexagonal MnTe

Antiferromagnetic hexagonal MnTe is a promising material for spintronic devices relying on the control of antiferromagnetic domain orientations. Here we report on neutron diffraction, magnetotransport, and magnetometry experiments on semiconducting epitaxial MnTe thin films together with density functional theory (DFT) calculations of the magnetic anisotropies. The easy axes of the magnetic moments within the hexagonal basal plane are determined to be along $\left<1\bar100\right>$ directions. The spin-flop transition and concomitant repopulation of domains in strong magnetic fields is observed. Using epitaxially induced strain the onset of the spin-flop transition changes from $\sim2$~T to $\sim0.5$~T for films grown on InP and SrF$_2$ substrates, respectively.

cond-mat.mtrl-sci↗

arXiv2018

Electrically induced and detected Néel vector reversal in a collinear antiferromagnet

Electrical detection of the 180 deg spin reversal, which is the basis of the operation of ferromagnetic memories, is among the outstanding challenges in the research of antiferromagnetic spintronics. Analogous effects to the ferromagnetic giant or tunneling magnetoresistance have not yet been realized in antiferromagnetic multilayers. Anomalous Hall effect (AHE), which has been recently employed for spin reversal detection in non-collinear antiferromagnets, is limited to materials that crystalize in ferromagnetic symmetry groups. Here we demonstrate electrical detection of the 180 deg Néel vector reversal in CuMnAs which comprises two collinear spin sublattices and belongs to an antiferromagnetic symmetry group with no net magnetic moment. We detect the spin reversal by measuring a second-order magnetotransport coefficient whose presence is allowed in systems with broken space inversion symmetry. The phenomenology of the non-linear transport effect we observe in CuMnAs is consistent with a microscopic scenario combining anisotropic magneto-resistance (AMR) with a transient tilt of the Néel vector due to a current-induced, staggered spin-orbit field. We use the same staggered spin-orbit field, but of a higher amplitude, for the electrical switching between reversed antiferromagnetic states which are stable and show no sign of decay over 25 hour probing times.

cond-mat.mtrl-sci↗