Direct magnetoelectric (ME) coupling between magnetic and ferroelectric orders can be realized in spiral magnets. In this work, Jahn-Teller Cu2+ ions and Ti4+ ions were introduced in SrFe12O19 to destroy...
While the unique geometrical frustration of pyrochlore Yb2Ti2O7 has attracted attention, the dielectric and other properties of this pyrochlore beyond frustrated magnetism are not well understood. Here, we report on the fascinating low-temperature dielectric relaxation of Yb2- xBa xTi2O7- δ ( x = 0–0.20) and demonstrate that this phenomenon is related to structural distortion. A-site Ba substitution, which increases the density of point defects and introduces a different atomic radius, enhances the chemical disorder and structural distortion. As a result, the increases in oxygen vacancies and nonmagnetic Ba2+ and Yb2+ ions dilute the ferromagnetic Yb3+–Yb3+ interactions, as indicated by the decrease in effective magnetic moment. On the other hand, the distorted octahedra facilitate the hopping of Yb ions, and the random distribution of Ba2+ ions at the Yb3+ sites gives rise to additional random fields, leading to significantly increased dielectric relaxation. The room-temperature dielectric constant is improved to ∼170, twice that of pristine Yb2Ti2O7. This work provides a comprehensive view of the structural, magnetic, and dielectric properties of Yb2Ti2O7 and lays the foundation for additional research into pyrochlore compounds.
Lead-free dielectric capacitors have attracted much attention in pulsed power systems for the rapid charge/discharge rate. While their recoverable energy storage density (W_rec) and efficiency (η) still need further improved...
Rare-earth titanate pyrochlores have
attracted considerable attention
for their unique magnetic frustration. Among those compounds, Yb2Ti2O7, a candidate for quantum spin
ice, has been extensively studied in its magnetic ground state. However,
works on its dielectric property and structure-property relationship
lag far more behind. Here, by preparing and investigating nonstoichiometric
Yb2–x
Ti2O7−δ (x = 0–0.15) ceramics, we demonstrate that
the samples with x ≤ 0.05 maintain a single-pyrochlore
phase, but the nonstoichiometry arouses significant structural distortion
and increased oxygen vacancy. As a result, the ferromagnetism, indicated
by a positive Curie-Weiss temperature, decreases almost linearly with
increasing x value. Remarkably composition-dependent
low-temperature dielectric relaxations have been observed. In addition,
through introducing nonstoichiometry, the relaxor degree of dielectric
behavior is enhanced, and the dielectric curve shows an altered shape.
The origin of this dielectric relaxation is attributed to the increased
structural distortion reflected by the changed bond length/angle,
since there is no phase transition in 90–300 K. Our work gives
a comprehensive view on the structural, magnetic, and dielectric properties
of Yb2Ti2O7, which is instructive
for further work on pyrochlores.
Here, we report the growth of (Sr, Ca) Nd2Fe2O7 single crystals with the Ruddlesden–Popper structure using an optical floating-zone method. A significantly anisotropic magneto-dielectric effect (MD), ab-plane and c-axial MD coefficients reaching −12.3% and −8.4% measured at 103 Hz in a 1 T magnetic field, can be obtained in a SrNd2Fe2O7 crystal at room temperature. The corresponding anisotropic MD ratio can be reached as high as 1.46. With an increase in the Ca concentration, the MD effect decreases dramatically and is eventually completely suppressed in both directions. Analysis of magnetic properties and 57Fe Mössbauer spectra suggests that the anisotropic MD effects in SrNd2Fe2O7 can be attributed to polaronic hopping between two neighboring Fe3+ ions through oxygen vacancies in an anisotropically antiferromagnetic matrix; the disappearance of the MD effect in Ca-doped SrNd2Fe2O7 is a consequence of the suppression of the antiferromagnetism. Our work suggests that the significantly anisotropic MD effect in SrNd2Fe2O7 crystals at room temperature can be used in magneto-dielectric controlled devices.
An
ethanol-assisted etching route using Zn powder as reductant
was developed to prepare the tunable pores in ITO films for modifying
the sheet resistance, ferromagnetism, and H2O2 sensitivity. Both XRD and XPS revealed that ITO is initially reduced
into metal In and Sn by Zn and then dissolved by HCl aqueous solution
diluted by ethanol, which makes the etching reactions controllable
and homogeneous. By adjusting the amount of Zn and/or ethanol, the
pore size and density were continuously tuned in the ranges of 20–280
nm and 49–213/μm2, respectively. With enlarging
the pore region, the ITO sheet resistance and ferromagnetism gradually
enhance. The pore formation decreases the ITO crystalline integrity
and carrier density and mainly contributes to the increase of sheet
resistance. The enhanced ferromagnetism arises from the increase of
oxygen vacancies induced by pores. Contrarily, the ITO ferromagnetism
can be greatly depressed by irradiating ITO with UV light to reduce
oxygen vacancies. By optimizing the pore structures and sheet resistance,
the porous ITOs made here increase the detection sensitivity of H2O2 up to 16.4 times in comparison to the commercial
ITO films.
Transition metal–vanadium
oxides Mn2V2O7 have recently attracted
much interest due to its rich
structural and magnetic phase transition. However, the systematic
studies on the effects of magnetic field (H) on these
phase transitions are still not available. Here, based on the high-quality
Mn2V2O7 crystals, the effects of
the magnetic field on its phase transitions were systematically studied.
When applied H is aligned along the [110] direction
of β-Mn2V2O7, there is a spin-flop
transition at low temperature (<17 K). The magnetic field–temperature
magnetic phase diagram is proposed. In addition, the magneto-crystalline
anisotropic energy of Mn2V2O7 shows
the unconventional “dome-like” feature, reaching its
maximum at 11 K, which may be related to the commensurate–incommensurate
magnetic phase transition determined by neutron scattering previously.
At the martensitic transformation around 270 K, 1 T H aligned along the [110] direction can induce the 1–2 K temperature
shift of martensitic transformation, simultaneously leading to a cusp-like
dielectric constant change (the maximum magneto-dielectric effect
∼ −18%). Transition-temperature shift induced by H can be quantitatively understood by thermodynamic Clausius–Clapeyron
relation. These results substantiate that the magnetic field has pronounced
effects on the phase transition in Mn2V2O7.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.