6 research outputs found
Electronic band structure changes across the antiferromagnetic phase transition of exfoliated MnPS probed by -ARPES
Exfoliated magnetic 2D materials enable versatile tuning of magnetization,
e.g., by gating or providing proximity-induced exchange interaction. However,
their electronic band structure after exfoliation has not been probed, most
likely due to their photochemical sensitivity. Here, we provide micron-scale
angle-resolved photoelectron spectroscopy of the exfoliated intralayer
antiferromagnet MnPS above and below the N\'{e}el temperature down to one
monolayer. The favorable comparison with density functional theory calculations
enables to identify the orbital character of the observed bands. Consistently,
we find pronounced changes across the N\'{e}el temperature for bands that
consist of Mn 3d and 3p levels of adjacent S atoms. The deduced orbital mixture
indicates that the superexchange is relevant for the magnetic interaction.
There are only minor changes between monolayer and thicker films demonstrating
the predominant 2D character of MnPS. The novel access is transferable to
other MPX materials (M: transition metal, P: phosphorus, X: chalcogenide)
providing a multitude of antiferromagnetic arrangements.Comment: 26 pages, 17 figure
Lattice dynamics and in-plane antiferromagnetism in MnxZn1-xPS3 across the entire composition range
peer reviewedAlloyed MnxZn1-xPS3 samples have been grown covering the whole compositional range and studied by means of Raman spectroscopy at temperatures from 4 to 850 K. Our results, supported by superconducting quantum interference device magnetic measurements, allowed us, on one hand, to complete the magnetic phase diagram of MnxZn1-xPS3 and establish x≥0.3 as the composition at which the alloy retains antiferromagnetism and, on the other hand, to identify the Raman signatures indicative of a magnetic transition. The origin of these Raman signatures is discussed in terms of spin-phonon coupling, resulting in the appearance of low- and high-frequency phonon modes. For the alloy, an assignation of the first- and second-order modes is provided with the aid of first-principles lattice-dynamical calculations. The compositional dependence of all phonon modes is described, and the presence of zone-folded modes is shown to take place for the alloy. Finally, a comparison of the Raman spectra of ZnPS3 to other compounds of the transition metal phosphorus trisulfide family allowed us to conclude that low-frequency phonon peaks exhibit an abnormally large broadening. This is consistent with previous claims on the occurrence of a second-order Jahn-Teller effect that takes place for ZnPS3 and Zn-rich MnxZn1-xPS3
Tuning Optical Activity of IV–VI Colloidal Quantum Dots in the Short-Wave Infrared (SWIR) Spectral Regime
The
achievement of tunable optical properties across a wide spectral
range, along with an efficient surface passivation of lead chalcogenide
(PbSe) colloidal quantum dots (CQDs), has significant importance for
scientific research and for technological applications. This paper
describes two comprehensive pathways to tune optical activities of
PbSe CQDs in the near-infrared (NIR, 0.75–1.4 μm) and
the short-wave infrared (SWIR, 1.4–3 μm) ranges. A one-pot
procedure enabled the growth of relatively large PbSe CQDs (with average
sizes up to 14 nm) exploiting programmable temperature control during
the growth process. These CQDs showed optical activity up to 3.2 μm.
In addition, PbSe/PbS core/shell CQDs prepared by an orderly injection
rate led to an energy red-shift of the absorption edge with the increase
of the shell thickness, whereas a postannealing treatment further
extended the band-edge energy toward the SWIR regime. A better chemical
stability of the CQDs with respect to that of PbSe core CQDs was attained
by shelling of PbSe by epitaxial layers of PbS, but limited to a short
duration (<1 day). However, air stability of the relatively large
PbSe as well as the PbSe/PbS CQDs over a prolonged period of time
(weeks) was achieved after a postsynthesis chlorination treatment
Insight into the Spin Properties in Undoped and Mn-Doped CdSe/CdS-Seeded Nanorods by Optically Detected Magnetic Resonance
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Electronic Band Structure Changes across the Antiferromagnetic Phase Transition of Exfoliated MnPS 3 Flakes Probed by μ-ARPES
Exfoliated magnetic 2D materials enable versatile tuning of magnetization, e.g., by gating or providing proximity-induced exchange interaction. However, their electronic band structure after exfoliation has not been probed, presumably due to their photochemical sensitivity. Here, we provide micrometer-scale angle-resolved photoelectron spectroscopy of the exfoliated intralayer antiferromagnet MnPS3 above and below the Néel temperature down to one monolayer. Favorable comparison with density functional theory calculations enables identifying the orbital character of the observed bands. Consistently, we find pronounced changes across the Néel temperature for bands consisting of Mn 3d and 3p levels of adjacent S atoms. The deduced orbital mixture indicates that the superexchange is relevant for the magnetic interaction. There are only minor changes between monolayer and thicker films, demonstrating the predominant 2D character of MnPS3. The novel access is transferable to other MPX3 materials (M: transition metal, P: phosphorus, X: chalcogenide), providing several antiferromagnetic arrangements