Pressure-Induced Electronic Mixing and Enhancement of Ferromagnetic Ordering in Eu<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>X</mml:mi></mml:math>(<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>X</mml:mi><mml:mo>=</mml:mo><mml:mi>Te</mml:mi></mml:math>, Se, S, O) Magnetic Semiconductors

Souza-Neto, N. M.; Haskel, D.; Tseng, Yuan-Chieh; Lapertot, G.

doi:10.1103/physrevlett.102.057206

Cited by 62 publications

(71 citation statements)

References 30 publications

(69 reference statements)

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“…A previous report [18] provides evidence for a direct correlation between Eu 4f -5d electronic mixing and the increase in ferromagnetic ordering temperature that takes place in EuO up to ≈14 GPa. Despite the presence of f -d mixing no evidence of mixed valency was found in this pressure regime where a stable, fractional (non-integer) occupation of 4f orbitals is found instead.…”

Section: +mentioning

confidence: 99%

“…Below 14 GPa a well-defined quantum state of fractional 4f (and 5d ) occupation evolves with pressure, resulting in a continuous increase in magnetic ordering temperature [18]. Between 14 and 44 GPa the Europium atoms display a mixed-valent state composed of discrete Eu 2+ and Eu 3+ states, homogenously distributed over volume and fluctuating with a characteristic frequency determined by the 4f bandwidth (f > ∼ 0.15 PHz).…”

Section: +mentioning

confidence: 99%

“…Consequently, the Mössbauer experiment sees a fast fluctuating valence [1] as a static average of both states while the XANES process is fast enough to separately probe both states. Interestingly, the proximity in the lifetime of the fluctuating valence state and lattice fluctuations (≈ 10 −13 ) may influence how the magnetism [9,18,19,23,25] and conductivity [17,25,26] of EuO respond to pressure as the 4f electronic bandwidth changes with lattice contraction. The general approximation "bond length is a unique function of bond valence" [11] is widely used to determine a material's valence based on crystal structure.…”

Section: +mentioning

confidence: 99%

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Reentrant Valence Transition in EuO at High Pressures: Beyond the Bond-Valence Model

Souza-Neto

Zhao

et al. 2012

Phys. Rev. Lett.

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The pressure-dependent relation between Eu valence and lattice structure in model compound EuO is studied with synchrotron-based x-ray spectroscopic and diffraction techniques. Contrary to expectation, a 7% volume collapse at ≈ 45 GPa is accompanied by a reentrant Eu valence transition into a lower valence state. In addition to highlighting the need for probing both structure and electronic states directly when valence information is sought in mixed-valent systems, the results also show that widely used bond-valence methods fail to quantitatively describe the complex electronic valence behavior of EuO under pressure.The phenomenon of mixed-valency in f -electron systems occurs when otherwise localized f -orbitals of RareEarth or Actinide elements hybridize in the solid with s,p,d electrons. A quantum superposition of differently occupied (valence) f -states emerges when the energy difference between competing single-valent states is smaller than the f -electron bandwidth, usually termed fluctuating valence state [1]. The onset of mixed-valency under applied pressure, chemical substitutions, or finite temperature has dramatic consequences on the macroscopic properties of f -electron systems including volume collapse [2], quenched magnetism [3], onset of superconductivity [4,5], Kondo physics [6], and quantum criticality [4,5]. Despite mixed-valency being central to f -electron physics, our ability to directly probe this peculiar quantum electronic state at high pressures is limited.EuO with its simple NaCl (B1) crystal structure is a model system to study valence effects upon lattice compression [7]. Eu-containing compounds are prototypical mixed-valent systems because Eu can display both trivalent (as most Rare-Earths ions do) and divalent electronic states at ambient conditions, the latter stabilized by a half-filled 4f orbital occupation ([Xe]4f 7 5d 0 6 sAdditionally, the ferromagneticsemiconductor character of EuO [7] coupled with perfect spin-polarization of electronic states near the Fermi level generated interest for possible applications of EuO in Spintronics [8]. A dramatic, three-fold increase in magnetic ordering temperature is observed under applied pressures of up to ≈14 GPa (or at strained interfaces), reaching a maximum T C ≈ 200 K but decreasing at higher pressures [9]. The relationship between crystal structure, electronic structure and magnetic ordering temperature has fueled much of the research in EuO over the last two decades, with the question of Eu valency remaining key for a complete understanding of this and other f -electron mixed-valent systems. In this Letter we report direct measurements of electronic valence and crystal structure in Europium monoxide (EuO) at pressures up to 90 GPa using x-ray absorption spectroscopy, nuclear forward scattering and x-ray diffraction techniques. Below 40 GPa a complex, pressuredependent valence is observed to fluctuate between Eu 2+and Eu 3+ states at a frequency f > ∼ ∆E/h ∼ 0.15 PetaHertz where ∆E is the 4f bandwidth. At higher pressures we obse...

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Section: +mentioning

confidence: 99%

Section: +mentioning

confidence: 99%

Section: +mentioning

confidence: 99%

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Reentrant Valence Transition in EuO at High Pressures: Beyond the Bond-Valence Model

Souza-Neto

Zhao

et al. 2012

Phys. Rev. Lett.

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“…85,86 EuO becomes ferromagnetic below 70K under ambient pressure and the Curie temperature is known to increase with pressure reaching 200K under 1.5 × 10 5 atmospheres. 87 Since its integration with with Si and GaN, 86 EuO has garnered much attention for its potential use in spintronic applications. Ferromagnetic superconductors are materials that exhibit intrinsic coexistence of superconductivity and ferromagnetism where the same electrons are believed to be superconducting and ferromagnetic simultaneously.…”

Section: Topological Superconductivity and Majorana Fermionsmentioning

confidence: 99%

Microscopic theory for a ferromagnetic nanowire/superconductor heterostructure: Transport, fluctuations, and topological superconductivity

Takei

Galitski

2012

Phys. Rev. B

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Motivated by the recent experiment of Wang et al. [Nature Physics 6, 389 (2010)], who observed a highly unusual transport behavior of ferromagnetic Cobalt nanowires proximity-coupled to superconducting electrodes, we study proximity effect and temperature-dependent transport in such a mesoscopic hybrid structure. It is assumed that the asymmetry in the tunneling barrier gives rise to the Rashba spin-orbit-coupling in the barrier that enables induced p-wave superconductivity in the ferromagnet to exist. We first develop a microscopic theory of Andreev scattering at the spin-orbit-coupled interface, derive a set of self-consistent boundary conditions, and find an expression for the p-wave mini-gap in terms of the microscopic parameters of the contact. Second, we study temperature-dependence of the resistance near the superconducting transition and find that it should generally feature a fluctuation-induced peak. The upturn in resistance is related to the suppression of the singleparticle density of states due to the formation of fluctuating pairs, whose tunneling is suppressed. In conclusion, we discuss this and related setups involving ferromagnetic nanowires in the context of one-dimensional topological superconductors. It is argued that to realize unpaired end Majorana modes, one does not necessarily need a half-metallic state, but a partial spin polarization may suffice. Finally, we propose yet another related class of material systems -ferromagnetic semiconductor wires coupled to ferromagnetic superconductors -where direct realization of Kitaev-Majorana model should be especially straightforward.

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“…The ferromagnetic ordering temperature T C of MgO doped with nitrogen is below 5 K in the bulk limiting its applications [4]. It has been proven that, in several works, the biaxial and hydrostatic pressure [19][20][21][22] significantly increases T C toward room temperature. For example, EuS reaches T C = 290 K at P = 88 GPa [19].…”

Section: Introductionmentioning

confidence: 99%

Enhancement of Ferromagnetic Ordering Curie Temperature in N-Doped MgO under Hydrostatic Pressure

Mir¹,

Bekkouche²,

Boukortt³

et al. 2012

MNSMS

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We have explored the magnetic properties of Nitrogen doped cubic MgO using the full potential linearized augmented plane wave (FP-LAPW) method. The unit cell has 128 atoms, and two Nitrogen atoms are placed in the positions of oxygen sites. This corresponds to 3.125% doping concentration. Our calculations predict that the ferromagnetic state, with a magnetic moment of about 1.0 μB per Nitrogen-dopant, is more favorable in energy than the nonmagnetic state, and the ferromagnetic correlations are influenced by the impurity bound state. The magnetic moment mainly arises from p orbital of Nitrogen which substitutes the Oxygen atom, with a little contribution from the Oxygen atoms surrounding Nitrogen atom. The resulting band structure and densities of states agree well with the recent theoretical works. The ferromagnetic ordering temperatures obtained from DFT simulations have been given in detail. Our results show that the pressure enhances the temperature in MgO:N.

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Pressure-Induced Electronic Mixing and Enhancement of Ferromagnetic Ordering in EuX(X=Te, Se, S, O) Magnetic Semiconductors

Cited by 62 publications

References 30 publications

Reentrant Valence Transition in EuO at High Pressures: Beyond the Bond-Valence Model

Reentrant Valence Transition in EuO at High Pressures: Beyond the Bond-Valence Model

Microscopic theory for a ferromagnetic nanowire/superconductor heterostructure: Transport, fluctuations, and topological superconductivity

Enhancement of Ferromagnetic Ordering Curie Temperature in N-Doped MgO under Hydrostatic Pressure

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