279 research outputs found
Diffusion-assisted molecular beam epitaxy of CuCrO thin films
Using molecular beam epitaxy (MBE) to grow multi-elemental oxides (MEO) is
generally challenging, partly due to difficulty in stoichiometry control.
Occasionally, if one of the elements is volatile at the growth temperature,
stoichiometry control can be greatly simplified using adsorption-controlled
growth mode. Otherwise, stoichiometry control remains one of the main hurdles
to achieving high quality MEO film growths. Here, we report another kind of
self-limited growth mode, dubbed diffusion-assisted epitaxy, in which excess
species diffuses into the substrate and leads to the desired stoichiometry, in
a manner similar to the conventional adsorption-controlled epitaxy.
Specifically, we demonstrate that using diffusion-assisted epitaxy,
high-quality epitaxial CuCrO films can be grown over a wide growth window
without precise flux control using MBE.Comment: Accepted to the special edition of JVSTA on Thin Film Deposition for
Materials Discover
Superconducting four-fold Fe(Te,Se) film on six-fold magnetic MnTe via hybrid symmetry epitaxy
Epitaxial Fe(Te,Se) thin films have been grown on various substrates but
never been realized on magnetic layers. Here we report the epitaxial growth of
four-fold Fe(Te,Se) film on a six-fold antiferromagnetic insulator, MnTe. The
Fe(Te,Se)/MnTe heterostructure shows a clear superconducting transition at
around 11 K and the critical magnetic field measurement suggests the origin of
the superconductivity to be bulk-like. Structural characterizations suggest
that the uniaxial lattice match between Fe(Te,Se) and MnTe allows a hybrid
symmetry epitaxy mode, which was recently discovered between Fe(Te,Se) and
Bi2Te3. Furthermore, Te/Fe flux ratio during deposition of the Fe(Te,Se) layer
is found to be critical for its superconductivity. Now that superconducting
Fe(Te,Se) can be grown on two related hexagonal platforms, Bi2Te3 and MnTe,
this result opens a new possibility of combining topological superconductivity
of Fe(Te,Se) with the rich physics in the intrinsic magnetic topological
materials (MnTe)n(Bi2Te3)m family.Comment: 19 pages, 5 figures, accepted by Nano Letter
Tuning Structural, Transport and Magnetic Properties of Epitaxial SrRuO3 through Ba-Substitution
The perovskite ruthenates (ARuO3, A = Ca, Ba, or Sr) exhibit unique
properties owing to a subtle interplay of crystal structure and electronic-spin
degrees of freedom. Here, we demonstrate an intriguing continuous tuning of
crystal symmetry from orthorhombic to tetragonal (no octahedral rotations)
phases in epitaxial SrRuO3 achieved via Ba-substitution (Sr1-xBaxRuO3 with 0 <
x < 0.7). An initial Ba-substitution to SrRuO3 not only changes the
ferromagnetic properties, but also tunes the perpendicular magnetic anisotropy
via flattening the Ru-O-Ru bond angle (to 180{\deg}), resulting in the maximum
Curie temperature and an extinction of RuO6 rotational distortions at x = 0.20.
For x > 0.2, the suppression of RuO6 octahedral rotational distortion
dominantly enhances the ferromagnetism in the system, though competing with the
impact of the RuO6 tetragonal distortion. Further increasing x > 0.2 gradually
enhances the tetragonal-type distortion, resulting in the tuning of Ru-4d
orbital occupancy and suppression of ferromagnetism. Our results demonstrate
that isovalent substitution of the A-site cations significantly and
controllably impacts both electronic and magnetic properties of perovskite
oxides
Hole doping in compositionally complex correlated oxide enables tunable exchange biasing
Magnetic interfaces and the phenomena arising from them drive both the design
of modern spintronics and fundamental research. Recently, it was revealed that
through designing magnetic frustration in configurationally complex entropy
stabilized oxides, exchange bias can occur in structurally single crystal
films. This eliminates the need for complex heterostructures and nanocomposites
in the design and control of magnetic response phenomena. In this work, we
demonstrate through hole doping of a high entropy perovskite oxide that tuning
of magnetic responses can be achieved. With detailed magnetometry, we show
magnetic coupling exhibiting a variety of magnetic responses including exchange
bias and antiferromagnetic spin reversal in the entropy stabilized ABO3
perovskite oxide La1-xSrx(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 family. We find that
manipulation of the A-site charge state can be used to balance magnetic phase
compositions and coupling responses. This allows for the creation of highly
tunable exchange bias responses. In the low Sr doping regime, a spin frustrated
region arising at the antiferromagnetic phase boundary is shown to directly
couple to the antiferromagnetic moments of the film and emerges as the dominant
mechanism, leading to a vertical shift of magnetization loops in response to
field biasing. At higher concentrations, direct coupling of antiferromagnetic
and ferromagnetic regions is observed. This tunability of magnetic coupling is
discussed within the context of these three competing magnetic phases,
revealing critical features in designing exchange bias through exploiting spin
frustration and disorder in high entropy oxides
Magnetic Texture in Insulating Single Crystal High Entropy Oxide Spinel Films
Magnetic insulators are important materials for a range of next generation
memory and spintronic applications. Structural constraints in this class of
devices generally require a clean heterointerface that allows effective
magnetic coupling between the insulating layer and the conducting layer.
However, there are relatively few examples of magnetic insulators which can be
synthesized with surface qualities that would allow these smooth interfaces and
precisely tuned interfacial magnetic exchange coupling which might be
applicable at room temperature. In this work, we demonstrate an example of how
the configurational complexity in the magnetic insulator layer can be used to
realize these properties. The entropy-assisted synthesis is used to create
single crystal (Mg0.2Ni0.2Fe0.2Co0.2Cu0.2)Fe2O4 films on substrates spanning a
range of strain states. These films show smooth surfaces, high resistivity, and
strong magnetic responses at room temperature. Local and global magnetic
measurements further demonstrate how strain can be used to manipulate magnetic
texture and anisotropy. These findings provide insight into how precise
magnetic responses can be designed using compositionally complex materials that
may find application in next generation magnetic devices
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