pulses. These isotropic changes in R correspond
to a temperature change of a fraction of a Kelvin
over the probing time interval.
We also observe these AMR symmetries in
higher-temperature measurements. However,
the AMR changes sign between the higher- and
lower-temperature data, as seen when comparing the transverse resistance signals in Figs. 2
and 3 with the corresponding measurements in
the first row of Fig. 4. The change in sign of the
AMR is further confirmed in fig. S3 (see also the
supplementary text), where the measured temperature dependence of AMR is shown and compared to calculations. From this comparison, we
can infer the preferred AFM spin-axis direction
for the given writing current direction. The experimental and theoretical AMR signs match if
the AFM spin axis aligns perpendicular to the
writing current. This is consistent with the predicted direction of the spin-orbit current-induced
fields and with the XMLD-PEEM results. Measurements at high magnetic fields shown in fig. S3 (see
also supplementary text) give further confirmation that the AFM spin axis aligns perpendicular
to the setting current pulses. These measurements
also highlight that our AFM memory can be read
and written by the staggered current-induced
fields and the memory state retained even in the
presence of strong magnetic fields.
The staggered current-induced fields that
we observe are not unique to CuMnAs. The
high–Néel temperature AFM Mn2Au (37) is another example in which the spin sublattices form
inversion partners and where theory predicts
large field-like torques of the form dMA;B=dt ∼
MA;B ; pA;B with pA ¼ −pB (19). From our microscopic density-functional calculations, we
obtain a current-induced field of around 20 Oe
per 107 A cm−2 in Mn2Au, which, combined with
its higher conductivity, may make this a favorable system for observing current-driven AFM
switching. AFMs that do not possess these specific symmetries can in principle be switched
by injecting a spin current into the AFM from a
spin-orbit–coupled nonmagnetic (NM) layer using
an applied in-plane electrical current via the
spin Hall effect, generating the antidamping-like
torque dMA;B=dt ∼ MA;B ; ðMA;B ; pÞ (19). The
same type of torque can be generated by the
spin-orbit Berry-curvature mechanism acting
at the inversion-asymmetric AFM/NM interface
or in bare AFM crystals with globally noncentro-symmetric unit cells like CuMnSb (19). Our experiments in CuMnAs, combined with the prospect
of other realizations of these relativistic nonequilibrium phenomena in AFMs, indicate that
AFMs are now ready to join the rapidly developing fields of basic and applied spintronics,
enriching this area of solid-state physics and
microelectronics by the range of unique characteristics of AFMs.
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We acknowledge support from the European Union (EU) European
Research Council Advanced (grant 268066); the Ministry of
Education of the Czech Republic (grant LM2011026); the Grant
Agency of the Czech Republic (grant 14-37427); the UK Engineering
and Physical Sciences Research Council (grant EP/K027808/1);
the EU 7th Framework Programme (grant REGPOT-CT-2013-316014
and FP7-People-2012-ITN-316657); HGF Programme VH-NG 513
and Deutsche Forschungsgemeinschaft SPP 1568; supercomputing
resources at Jülich Supercomputing Centre and RWTH Aachen
University; and Diamond Light Source for the allocation of
beamtime under proposal number SI-12504. We thank C. Nelson
for providing the scanning transmission electron microscopy
Figs. S1 to S3
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11 March 2015; accepted 4 January 2016
Published online 14 January 2016
Holocene deceleration of the
Greenland Ice Sheet
Joseph A. MacGregor,1 William T. Colgan,2† Mark A. Fahnestock,3
Mathieu Morlighem,4 Ginny A. Catania,1,5 John D. Paden,6 S. Prasad Gogineni6
Recent peripheral thinning of the Greenland Ice Sheet is partly offset by interior thickening
and is overprinted on its poorly constrained Holocene evolution. On the basis of the ice
sheet’s radiostratigraphy, ice flow in its interior is slower now than the average speed over
the past nine millennia. Generally higher Holocene accumulation rates relative to modern
estimates can only partially explain this millennial-scale deceleration. The ice sheet’s
dynamic response to the decreasing proportion of softer ice from the last glacial period
and the deglacial collapse of the ice bridge across Nares Strait also contributed to this
pattern. Thus, recent interior thickening of the Greenland Ice Sheet is partly an ongoing
dynamic response to the last deglaciation that is large enough to affect interpretation of
its mass balance from altimetry.
The dynamics of the Greenland Ice Sheet (GrIS) are coupled intimately with the sur- rounding ocean (1), overlying atmosphere (2), and underlying lithosphere (3). The large range of time scales spanned by these
interactions and the GrIS’s own internal dynamics
(4) challenge our ability to predict GrIS evolution
within the context of ongoing Holocene climate
change (5, 6).
Despite a rapidly warming climate (6), recent
dramatic changes in ocean-terminating outlet
glaciers along the margin of the GrIS (7–9), its
vulnerability to further oceanic erosion (10), and
a sustained negative total mass balance (11–13),
more than half of the GrIS interior is presently
thickening (8, 14–16), and a portion of its south-
western margin is decelerating (17). Climate his-
tories reconstructed from ice cores show that the
GrIS persisted even when atmospheric temper-
atures were higher by several degrees Celsius (18)
and insolation forcing was larger than at present
(19). Reconciling these observations is critical to
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