Combining long-range magnetic order with polarity in
the same structure
is a prerequisite for the design of (magnetoelectric) multiferroic
materials. There are now several demonstrated strategies to achieve
this goal, but retaining magnetic order above room temperature remains
a difficult target. Iron oxides in the +3 oxidation state have high
magnetic ordering temperatures due to the size of the coupled moments.
Here we prepare and characterize ScFeO3 (SFO), which under
pressure and in strain-stabilized thin films adopts a polar variant
of the corundum structure, one of the archetypal binary oxide structures.
Polar corundum ScFeO3 has a weak ferromagnetic ground state
below 356 K—this is in contrast to the purely antiferromagnetic
ground state adopted by the well-studied ferroelectric BiFeO3.
Pulsed laser deposition has been used to artificially
construct
the n = 3 Ruddlesden–Popper structure La2Sr2Mn3O10 in epitaxial thin
film form by sequentially layering La1–xSrxMnO3 and SrO unit
cells aided by in situ reflection high energy electron diffraction
monitoring. The interval deposition technique was used to promote
two-dimensional SrO growth. X-ray diffraction and cross-sectional
transmission electron microscopy indicated that the trilayer structure
had been formed. A site ordering was found to differ from that expected
thermodynamically, with the smaller Sr2+ predominantly
on the R site due to kinetic trapping of the deposited cation sequence.
A dependence of the out-of-plane lattice parameter on growth pressure
was interpreted as changing the oxygen content of the films. Magnetic
and transport measurements on fully oxygenated films indicated a frustrated
magnetic ground state characterized as a spin glass-like magnetic
phase with the glass temperature Tg ≈
34 K. The magnetic frustration has a clear in-plane (ab) magnetic anisotropy, which is maintained up to temperatures of
150 K. Density functional theory calculations suggest competing antiferromagnetic
and ferromagnetic long-range orders, which are proposed as the origin
of the low-temperature glassy state.
Ferroelectric (FE)-HfO2 based FETs (FEFETs) are one of the most promising candidates for emerging memories. However, the FE material suffers from a unique reliability phenomenon known as imprint: the coercive voltage shifts during data retention, which has been regarded as a major issue for memory operation, while the mechanism causing it is still under research. In this paper, imprint and its recovery in FE-HfO2 are investigated in detail by comprehensive electrical measurements to reveal its underlying mechanism including the cause of asymmetric coercive voltage shifts. The recovery measurements clarify that domain switching is indispensable for the recovery from imprint. The sub-loop imprint effect shows that imprint and its recovery must be independent for each domain. In addition, switching time measurements and corresponding fitting results with the nucleation-limited-switching (NLS) model strongly indicate that imprint is caused by domainseeds-pinning. Based on these results, we conclude that charge trapping and de-trapping affecting activation barriers for domain switching, accompanied by domain switching is responsible for imprint and its recovery.
The cubic polymorph of the binary transition metal pnictide (TMP) MnSb, c-MnSb, has been predicted to be a robust half-metallic ferromagnetic (HMF) material with minority spin gap & 1 eV. Here, MnSb epilayers are grown by molecular beam epitaxy (MBE) on GaAs and In 0:5 Ga 0:5 As(111) substrates and analyzed using synchrotron radiation X-ray di®raction. We¯nd polymorphic growth of MnSb on both substrates, where c-MnSb co-exists with the ordinary niccolite n-MnSb polymorph. The grain size of the c-MnSb is of the order of tens of nanometer on both substrates and its appearance during MBE growth is independent of the very di®erent epitaxial strain from the GaAs (3.1%) and In 0:5 Ga 0:5 As (0.31%) substrates.
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