Ferrimagnetic A2BB′O6 double perovskites, such as Sr2FeMoO6, are important spin‐polarized conductors. Introducing transition metals at the A‐sites offers new possibilities to increase magnetization ...and tune magnetoresistance. Herein we report a ferrimagnetic double perovskite, Mn2FeReO6, synthesized at high pressure which has a high Curie temperature of 520 K and magnetizations of up to 5.0 μB which greatly exceed those for other double perovskite ferrimagnets. A novel switching transition is discovered at 75 K where magnetoresistance changes from conventional negative tunneling behavior to large positive values, up to 265 % at 7 T and 20 K. Neutron diffraction shows that the switch is driven by magnetic frustration from antiferromagnetic Mn2+ spin ordering which cants Fe3+ and Re5+ spins and reduces spin‐polarization. Ferrimagnetic double perovskites based on A‐site Mn2+ thus offer new opportunities to enhance magnetization and control magnetoresistance in spintronic materials.
Double‐perovskite magnetism: The double perovskite Mn2FeReO6 synthesized at high pressure has magnetic transition‐metal cations at all sites. High‐spin Mn2+ cations lead to record magnetizations for double‐perovskite ferrimagnets and their frustrated magnetic order at 75 K switches magnetoresistance from negative to large positive values at low temperatures.
Superconductivity in (Ba,K)SbO3 Kim, Minu; McNally, Graham M.; Kim, Hun-Ho ...
Nature materials,
06/2022, Volume:
21, Issue:
6
Journal Article
Peer reviewed
Open access
Abstract
(Ba,K)BiO
3
constitute an interesting class of superconductors, where the remarkably high superconducting transition temperature
T
c
of 30 K arises in proximity to charge density wave order. ...However, the precise mechanism behind these phases remains unclear. Here, enabled by high-pressure synthesis, we report superconductivity in (Ba,K)SbO
3
with a positive oxygen–metal charge transfer energy in contrast to (Ba,K)BiO
3
. The parent compound BaSbO
3−
δ
shows a larger charge density wave gap compared to BaBiO
3
. As the charge density wave order is suppressed via potassium substitution up to 65%, superconductivity emerges, rising up to
T
c
= 15 K. This value is lower than the maximum
T
c
of (Ba,K)BiO
3
, but higher by more than a factor of two at comparable potassium concentrations. The discovery of an enhanced charge density wave gap and superconductivity in (Ba,K)SbO
3
indicates that strong oxygen–metal covalency may be more essential than the sign of the charge transfer energy in the main-group perovskite superconductors.
Cation ordering in ABO3 perovskites can lead to interesting and useful phenomena such as ferrimagnetism and high magnetoresistance by spin polarized conduction in Sr2FeMoO6. We used high pressures ...and temperatures to synthesize the cation ordered AA′BB′O6 perovskites CaMnFeReO6, CaMnMnReO6, and Ca(Mn0.5Cu0.5)FeReO6. These have columnar A/A′ and rocksalt B/B′ cation orders, as found in the recently discovered double double perovskite MnNdMnSbO6, and partial Mn/Cu order over tetrahedral and square planar A′ sites in Ca(Mn0.5Cu0.5)FeReO6 demonstrates that triple double cation order is possible. Neutron diffraction reveals complex ferrimagnetic orders in all three materials; CaMnFeReO6 and Ca(Mn0.5Cu0.5)FeReO6 have large room temperature magnetizations with low temperature switching of magnetoresistance in the latter material, and CaMnMnReO6 displays a high coercivity of 1.3 T at low temperatures.
Herein, we present results of the 121Sb Mössbauer spectroscopy in perovskite antimonates Ba1–x K x SbO3, sibling compounds of the well-known high-T c superconductors Ba1–x K x BiO3. Two Sb valence ...states SbIII and SbV, forming a charge-density-wave (CDW) order, are unambiguously revealed in un- and under-doped phases at x = 0–0.5. As the CDW order is suppressed at x = 0.65, the compound becomes superconducting and all of the Sb sites become equivalent with the intermediate valence of +4.65, consistent with that anticipated from the potassium content. These results provide the direct evidence of metal s electrons participating in the formation of the CDW order and superconductivity in the material, and thus they have important implications for clarifying the underlying mechanism related to mixed valence and potential valence fluctuations of metal ions. The use of Mössbauer active nuclei offers a deeper insight into the structural properties and superconductivity in mixed-valence main-group oxides.
MnFe3O5 was synthesized under a pressure of 10 GPa at 1400 °C. MnFe3O5 has an orthorhombic structure (space group Cmcm, a = 2.9137(1), b = 9.8565(7) and c = 12.6143(6) Å at 300 K) and is ...isostructural with Fe4O5. Magnetic measurements reveal an antiferromagnetic transition at 350 K and a broad Curie transition at 150 K, similar to the spin ordering temperatures of Fe4O5. Variable temperature synchrotron X‐ray diffraction shows that the structure undergoes anisotropic thermal expansion below 350 K, but no long range charge ordering is observed in the crystal structure.
Ferrimagnetic A2BB′O6 double perovskites, such as Sr2FeMoO6, are important spin‐polarized conductors. Introducing transition metals at the A‐sites offers new possibilities to increase magnetization ...and tune magnetoresistance. Herein we report a ferrimagnetic double perovskite, Mn2FeReO6, synthesized at high pressure which has a high Curie temperature of 520 K and magnetizations of up to 5.0 μB which greatly exceed those for other double perovskite ferrimagnets. A novel switching transition is discovered at 75 K where magnetoresistance changes from conventional negative tunneling behavior to large positive values, up to 265 % at 7 T and 20 K. Neutron diffraction shows that the switch is driven by magnetic frustration from antiferromagnetic Mn2+ spin ordering which cants Fe3+ and Re5+ spins and reduces spin‐polarization. Ferrimagnetic double perovskites based on A‐site Mn2+ thus offer new opportunities to enhance magnetization and control magnetoresistance in spintronic materials.
Der Doppelperowskit Mn2FeReO6, der unter hohem Druck synthetisiert wurde, ist an allen Positionen mit magnetischen Übergangsmetallkationen besetzt. High‐Spin‐Mn2+‐Ionen halten den Rekord bei der Magnetisierung für Doppelperowskit‐Ferrimagnete, und deren Magnetwiderstand wechselt bei 75 K von negativen zu stark positiven Werten bei tiefen Temperaturen.
(Ba,K)BiO
constitute an interesting class of superconductors, where the remarkably high superconducting transition temperature T
of 30 K arises in proximity to charge density wave order. However, the ...precise mechanism behind these phases remains unclear. Here, enabled by high-pressure synthesis, we report superconductivity in (Ba,K)SbO
with a positive oxygen-metal charge transfer energy in contrast to (Ba,K)BiO
. The parent compound BaSbO
shows a larger charge density wave gap compared to BaBiO
. As the charge density wave order is suppressed via potassium substitution up to 65%, superconductivity emerges, rising up to T
= 15 K. This value is lower than the maximum T
of (Ba,K)BiO
, but higher by more than a factor of two at comparable potassium concentrations. The discovery of an enhanced charge density wave gap and superconductivity in (Ba,K)SbO
indicates that strong oxygen-metal covalency may be more essential than the sign of the charge transfer energy in the main-group perovskite superconductors.
Ferrimagnetic A sub(2)BB'O sub(6) double perovskites, such as Sr sub(2)FeMoO sub(6), are important spin-polarized conductors. Introducing transition metals at the A-sites offers new possibilities to ...increase magnetization and tune magnetoresistance. Herein we report a ferrimagnetic double perovskite, Mn sub(2)FeReO sub(6), synthesized at high pressure which has a high Curie temperature of 520K and magnetizations of up to 5.0 mu sub(B) which greatly exceed those for other double perovskite ferrimagnets. A novel switching transition is discovered at 75K where magnetoresistance changes from conventional negative tunneling behavior to large positive values, up to 265% at 7T and 20K. Neutron diffraction shows that the switch is driven by magnetic frustration from antiferromagnetic Mn super(2+) spin ordering which cants Fe super(3+) and Re super(5+) spins and reduces spin-polarization. Ferrimagnetic double perovskites based on A-site Mn super(2+) thus offer new opportunities to enhance magnetization and control magnetoresistance in spintronic materials. Double-perovskite magnetism: The double perovskite Mn sub(2)FeReO sub(6) synthesized at high pressure has magnetic transition-metal cations at all sites. High-spin Mn super(2+) cations lead to record magnetizations for double-perovskite ferrimagnets and their frustrated magnetic order at 75K switches magnetoresistance from negative to large positive values at low temperatures.
Abstract
Ferrimagnetic A
2
BB′O
6
double perovskites, such as Sr
2
FeMoO
6
, are important spin‐polarized conductors. Introducing transition metals at the A‐sites offers new possibilities to increase ...magnetization and tune magnetoresistance. Herein we report a ferrimagnetic double perovskite, Mn
2
FeReO
6
, synthesized at high pressure which has a high Curie temperature of 520 K and magnetizations of up to 5.0 μ
B
which greatly exceed those for other double perovskite ferrimagnets. A novel switching transition is discovered at 75 K where magnetoresistance changes from conventional negative tunneling behavior to large positive values, up to 265 % at 7 T and 20 K. Neutron diffraction shows that the switch is driven by magnetic frustration from antiferromagnetic Mn
2+
spin ordering which cants Fe
3+
and Re
5+
spins and reduces spin‐polarization. Ferrimagnetic double perovskites based on A‐site Mn
2+
thus offer new opportunities to enhance magnetization and control magnetoresistance in spintronic materials.
MnFe
3
O
5
was synthesized under a pressure of 10 GPa at 1400 °C. MnFe
3
O
5
has an orthorhombic structure (space group
Cmcm
,
a
= 2.9137(1),
b
= 9.8565(7) and
c
= 12.6143(6) Å at 300 K) and is ...isostructural with Fe
4
O
5
. Magnetic measurements reveal an antiferromagnetic transition at 350 K and a broad Curie transition at 150 K, similar to the spin ordering temperatures of Fe
4
O
5
. Variable temperature synchrotron X‐ray diffraction shows that the structure undergoes anisotropic thermal expansion below 350 K, but no long range charge ordering is observed in the crystal structure.
PDF
