23 research outputs found
Magnetization reorientation due to the superconducting transition in heavy-metal heterostructures
Recent theoretical and experimental work has demonstrated how the
superconducting critical temperature () can be modified by rotating the
magnetization of a single homogeneous ferromagnet proximity-coupled to the
superconducting layer. This occurs when the superconductor and ferromagnet are
separated by a thin heavy normal metal that provides an enhanced interfacial
Rashba spin-orbit interaction. We consider the reciprocal effect: magnetization
reorientation driven by the superconducting phase transition. We solve the
tight-binding Bogoliubov-de Gennes equations on a lattice self-consistently and
find that the relative angle between the spin-orbit field and the magnetization
gives rise to a contribution in the free energy even in the normal state due to
band-structure effects. For temperatures below , superconductivity gives
rise to a competing contribution. By lowering the temperature, in addition to
reorientation of the favored magnetization direction from in-plane to
out-of-plane, a in-plane rotation for thicker ferromagnetic layers is
possible. Furthermore, computation of of the structure in the ballistic
limit shows a dependence on the in-plane orientation of the magnetization, in
contrast to our previous result on the diffusive limit. This finding is
relevant with respect to thin-film heterostructures since these are likely to
be in the ballistic regime of transport. Finally, we discuss the experimental
feasibility of observing the magnetic anisotropy induced by the superconducting
transition when other magnetic anisotropies, such as the shape anisotropy for a
ferromagnetic film, are taken into account. Our work suggests that the
superconducting condensation energy in principle can trigger a reorientation of
the magnetization of a thin-film ferromagnet upon lowering the temperature
below , in particular for ferromagnets with weak magnetic anisotropies.Comment: 11 pages, 10 figure
Controlling the Superconducting Transition by Rotation of an Inversion Symmetry-Breaking Axis
We consider a hybrid structure where a material with Rashba-like spin-orbit
coupling is proximity coupled to a conventional superconductor. We find that
the superconducting critical temperature can be tuned by rotating the
vector characterizing the axis of broken inversion symmetry.
This is explained by a leakage of -wave singlet Cooper pairs out of the
superconducting region, and by conversion of -wave singlets into other types
of correlations, among these -wave odd-frequency pairs robust to impurity
scattering. These results demonstrate a conceptually different way of tuning
compared to the previously studied variation of in magnetic
hybrids.Comment: 4 pages, (11 pages including Supplemental Material), 3 figure
Magnetization reorientation due to the superconducting transition in heavy-metal heterostructures
© 2019 American Physical Society. UK. Recent theoretical and experimental work has demonstrated how the superconducting critical temperature (Tc) can be modified by rotating the magnetization of a single homogeneous ferromagnet proximity-coupled to the superconducting layer. This occurs when the superconductor and ferromagnet are separated by a thin heavy normal metal that provides an enhanced interfacial Rashba spin-orbit interaction. In the present work, we consider the reciprocal effect: magnetization reorientation driven by the superconducting phase transition. We solve the tight-binding Bogoliubov-de Gennes equations on a lattice self-consistently and compute the free energy of the system. We find that the relative angle between the spin-orbit field and the magnetization gives rise to a contribution in the free energy even in the normal state, T>Tc, due to band-structure effects. For temperatures below Tc, superconductivity gives rise to a competing contribution. We demonstrate that by lowering the temperature, in addition to reorientation of the favored magnetization direction from in-plane to out-of-plane, a π/4 in-plane rotation for thicker ferromagnetic layers is possible. Furthermore, computation of Tc of the structure in the ballistic limit shows a dependence on the in-plane orientation of the magnetization, in contrast to our previous result on the diffusive limit. This finding is relevant with respect to thin-film heterostructures since these are likely to be in the ballistic regime of transport rather than in the diffusive regime. Finally, we discuss the experimental feasibility of observing the magnetic anisotropy induced by the superconducting transition when other magnetic anisotropies, such as the shape anisotropy for a ferromagnetic film, are taken into account. Our work suggests that the superconducting condensation energy in principle can trigger a reorientation of the magnetization of a thin-film ferromagnet upon lowering the temperature below Tc, in particular for ferromagnets with weak magnetic anisotropies
Complete suppression and N\'eel triplets-mediated exchange in antiferromagnet-superconductor-antiferromagnet trilayers
An antiferromagnetic insulator (AFI) bearing a compensated interface to an
adjacent conventional superconductor (S) has recently been predicted to
generate N\'eel triplet Cooper pairs, whose amplitude alternates sign in space.
Here, we theoretically demonstrate that such N\'eel triplets enable control of
the superconducting critical temperature in an S layer via the angle between
the N\'eel vectors of two enclosing AFI layers. This angle dependence changes
sign with the number of S monolayers providing a distinct signature of the
N\'eel triplets. Furthermore, we show that the latter mediate a similarly
distinct exchange interaction between the two AFIs' N\'eel vectors.Comment: 7 pages, 4 figure
Superconductivity-induced change in magnetic anisotropy in epitaxial ferromagnet-superconductor hybrids with spin-orbit interaction
The interaction between superconductivity and ferromagnetism in thin film
superconductor/ferromagnet heterostructures is usually reflected by a change in
superconductivity of the S layer set by the magnetic state of the F layers.
Here we report the converse effect: transformation of the magnetocrystalline
anisotropy of a single Fe(001) layer, and thus its preferred magnetization
orientation, driven by the superconductivity of an underlying V layer through a
spin-orbit coupled MgO interface. We attribute this to an additional
contribution to the free energy of the ferromagnet arising from the controlled
generation of triplet Cooper pairs, which depends on the relative angle between
the exchange field of the ferromagnet and the spin-orbit field. This is
fundamentally different from the commonly observed magnetic domain modification
by Meissner screening or domain wall-vortex interaction and offers the ability
to fundamentally tune magnetic anisotropies using superconductivity - a key
step in designing future cryogenic magnetic memories.Comment: Submitted for publicatio
Superconductivity assisted change of the perpendicular magnetic anisotropy in V/MgO/Fe junctions
Controlling the perpendicular magnetic anisotropy (PMA) in thin films has
received considerable attention in recent years due to its technological
importance. PMA based devices usually involve heavy-metal
(oxide)/ferromagnetic-metal bilayers, where, thanks to interfacial spin-orbit
coupling (SOC), the in-plane (IP) stability of the magnetization is broken.
Here we show that in V/MgO/Fe(001) epitaxial junctions with competing in-plane
and out-of-plane (OOP) magnetic anisotropies, the SOC mediated interaction
between a ferromagnet (FM) and a superconductor (SC) enhances the effective PMA
below the superconducting transition. This produces a partial magnetization
reorientation without any applied field for all but the largest junctions,
where the IP anisotropy is more robust; for the smallest junctions there is a
reduction of the field required to induce a complete OOP transition
() due to the stronger competition between the IP and OOP
anisotropies. Our results suggest that the degree of effective PMA could be
controlled by the junction lateral size in the presence of superconductivity
and an applied electric field. We also discuss how the field
could be affected by the interaction between magnetic stray fields and
superconducting vortices. Our experimental findings, supported by numerical
modelling of the ferromagnet-superconductor interaction, open pathways to
active control of magnetic anisotropy in the emerging dissipation-free
superconducting spin electronics.Comment: Submitte
Superconductivity-induced change in magnetic anisotropy in epitaxial ferromagnet-superconductor hybrids with spin-orbit interaction
The interaction between superconductivity and ferromagnetism in thin film superconductor/ferromagnet
heterostructures is usually reflected by a change in superconductivity of the S layer set by the magnetic state
of the F layers. Here we report the converse effect: transformation of the magnetocrystalline anisotropy of a
single Fe(001) layer, and thus its preferred magnetization orientation, driven by the superconductivity of an
underlying V layer through a spin-orbit coupled MgO interface. We attribute this to an additional contribution
to the free energy of the ferromagnet arising from the controlled generation of triplet Cooper pairs, which
depends on the relative angle between the exchange field of the ferromagnet and the spin-orbit field. This is
fundamentally different from the commonly observed magnetic domain modification by Meissner screening
or domain wall-vortex interaction, and it offers the ability to fundamentally tune magnetic anisotropies using
superconductivity—a key step in designing future cryogenic magnetic memories
Spin injection and spin relaxation in odd-frequency superconductors
The spin transport inside an odd-frequency spin-triplet superconductor differs from that of a conventional superconductor due to its distinct symmetry properties. We study spin transport inside an emergent odd-frequency superconductor by replacing the spin-singlet gap matrix in the Usadel equation with a matrix representing spin-triplet pairing that is odd under inversion of energy. We show that the peculiar nature of the density of states allows for an even larger spin injection than in the normal state. Moreover, when the odd-frequency pairing inherits its temperature dependence from a conventional superconductor through the proximity effect, the density of states can transition from gapless to gapped as the temperature decreases. At the transition point, the spin accumulation inside the odd-frequency superconductor is peaked and larger than in the normal state. While the spin-flip scattering time is known to decrease below the superconducting transition temperature in conventional superconductors, we find that the same is true for the spin-orbit scattering time in odd-frequency superconductors. This renormalization is particularly large for energies close to the gap edge, if such a gap is present
Spin injection and spin relaxation in odd-frequency superconductors
The spin transport inside an odd-frequency spin-triplet superconductor differs from that of a conventional superconductor due to its distinct symmetry properties. We study spin transport inside an emergent odd-frequency superconductor by replacing the spin-singlet gap matrix in the Usadel equation with a matrix representing spin-triplet pairing that is odd under inversion of energy. We show that the peculiar nature of the density of states allows for an even larger spin injection than in the normal state. Moreover, when the odd-frequency pairing inherits its temperature dependence from a conventional superconductor through the proximity effect, the density of states can transition from gapless to gapped as the temperature decreases. At the transition point, the spin accumulation inside the odd-frequency superconductor is peaked and larger than in the normal state. While the spin-flip scattering time is known to decrease below the superconducting transition temperature in conventional superconductors, we find that the same is true for the spin-orbit scattering time in odd-frequency superconductors. This renormalization is particularly large for energies close to the gap edge, if such a gap is present