Magnetic properties in Ca-doped Eu hexaborides

Rhyee, Jong‐Soo; Oh, Byung Ho; Cho, B. K.; Kim, Hyoung Chan; Jung, Myung‐Hwa

doi:10.1103/physrevb.67.212407

Cited by 13 publications

(14 citation statements)

References 13 publications

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“…Small Ca doping at Eu-site shows the systematic suppression of T C . For Ca doping over 35%, an AF transition is observed in temperaturedependent magnetization [4]. Eu 1Àx La x B 6 also shows similar features, the suppression of T C for xo0:1 and the AF transition for larger doping [5].…”

supporting

confidence: 54%

Electronic and magnetic structures of EuB6: The effects of pressure and doping

Shim

Min

2006

Journal of Magnetism and Magnetic Materials

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supporting

confidence: 54%

Electronic and magnetic structures of EuB6: The effects of pressure and doping

Shim

Min

2006

Journal of Magnetism and Magnetic Materials

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“…Thus, the fRm(1) has a cubic A 1g symmetry. Instead, fRm (2) and fRm(3) did not appear on the T 2g channel probed with the (a, b) configuration (figure 2(b)) but were clearly observed on the same channel in the (c, a) case ( figure 2(d)). Thus, we concluded that the symmetry of fRm(2) and fRm(3) is A, of a non-cubic group.…”

Section: Resultsmentioning

confidence: 96%

“…The spectral intensity response was five times larger when the excitation was the 514.5 nm, indicating a possible resonant behavior. We shall label these extra modes as forbidden Raman modes fRm(1), fRm (2), and fRm(3), respectively. The other compounds of the Ca 1−x Eu x B 6 series showed similar spectra.…”

Section: Methodsmentioning

confidence: 99%

“…In particular, the family R 1−x A x B 6 (A = magnetic rare earth) has attracted considerable interest due to the intriguing connections between their magnetic [2], transport [3], and optical properties [4,5]. The available crystallographic data indicate that these compounds are cubic with the unit cell belonging to the O h space group (a ≈ 4.19Å) [6].…”

Section: Introductionmentioning

confidence: 99%

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Evidence for a subtle structural symmetry breaking in EuB₆

Martinho¹,

Rettori²,

Dalpian³

et al. 2009

J. Phys.: Condens. Matter

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This work presents a systematic Raman scattering study and first-principles calculations for the EuB 6 system. Evidence for the presence of an incipient (∼1×10 −4Å ) tetragonal symmetry break of its crystalline structure was found. Forbidden Raman modes at ω fRm(1) ∼ 1170 cm −1 , ω fRm(2) ∼ 1400 cm −1 , and ω fRm(3) ∼ 1500 cm −1 were observed. The tetragonal symmetry of ω fRm(2) and ω fRm(3) together with spin-polarized first-principles simulations of the structural and magnetic properties fully support such a break of symmetry. Our data and calculations explain the occurrence of ferromagnetism in Eu hexaborides, previously reported.

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“…We propose an electronic band model that explains all the spectral changes coherently. It allows simultaneous solutions to the aforementioned two issues.Single-crystal EuB 6 samples were synthesized by the boro-thermal flux method [11,12]. The normal incidence reflectivity, R(ω), was measured at 5 K≤T≤100 K in the 2 meV−1 eV range using a Fourier transform spectrometer with the in situ overcoating technique [13].…”

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confidence: 99%

Multiple-Structure Optical Spectral Weight Transfer in Ferromagnetic EuB6

Kim¹,

Jung²,

Choi³

2008

J. Korean Phy. Soc.

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We present the first wide range (2 meV−5.5 eV) optical conductivity of EuB6 from reflectivity and ellipsometry measurements. Upon the ferromagnetic transition at Tc=15.5 K, interband transition σ1(ω) decreases at three different energy ω=0.5, 1.4, 2.75 eV and the lost spectral weight is transferred to the Drude σ1(ω) at ω <0.33 eV. We succeeded in explaining this unprecedented multiple-energy σ1(ω) change using LDA+U calculated band structure by Kunes and Pickett (Phys. Rev. B, 69, 165111). Our finding supports strongly that (1) EuB6 is a semimetal and (2) the exchange-driven band splitting is the primary source of the drastic ρ(T ) and ω 2 p changes at T < Tc.PACS numbers: 78.20. Ls,78.40.Kc,71.20.Eh,71.70.Gm Interplay of itinerant carrier with localized magnetic moment can lead to novel magneto-resistance effect in solid. When the moments align with long range ferromagnetic order, dc-resistivity exhibits a drastic change as seen in EuO and (Ga,Mn)As. Theories such as the Kondo-lattice model, Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction and spin-polaron model propose possible microscopic mechanism of the carrier-moment coupling in magnetic conductors.Europium hexaboride EuB 6 is a simple cubic compound where dilute conducting carrier (n ∼ 10 19 cm −3 ) coexists with localized 4f spin of Eu +2 (S=7/2). The latter undergoes ferromagnetic (FM) transition at T c =15.5 K where simultaneously dc-resistivity ρ drops sharply [1] and the infrared plasma frequency ω 2 p (=4πe 2 n/m) suddenly increases [2]. Such dramatic FM-driven changes were seen in the manganites like (La 0.7 Ca 0.3 )MnO 3 [3] whereas EuB 6 being free from complications like lattice distortion and random substitution offers a cleaner and ideal example of ferromagnetic metal where the carrier-moment interaction can be studied in more fundamental level.In the Kondo-lattice model itinerant electron band is split in FM phase by the s-f exchange interaction into two spin-polarized sub-bands. Kreissl and Nolting applied this theory to EuB 6 to find that the band splitting brings about a significant increase of the carrier density [4]. The ρ(T ) drop and ω 2 p increase are attributed to it. In contrast Hirsch proposed an alternative model that conduction band becomes broader in FM state because the spin-polarization reduces the bond-charge repulsion effect [5,6]. This band width increase or equivalently carrier mass decrease is considered as a source of the enhanced metallicity. Pereira et al. suggested yet another scenario that at T>T c the disordered spin background can localize the carriers via their exchange interaction and it introduces a mobility edge in the conduction band [7]. FM spin alignment reduces the localization effect, lowering the mobility edge position, and the carriers become delocalized. This theoretical diversity shows that EuB 6 is an important prototype of metallic ferromagnetism. At present it is not clear which model is correctly describing it.Probing electronic band structure is an essential step to solve this issue. Accordin...

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Magnetic properties in Ca-doped Eu hexaborides

Cited by 13 publications

References 13 publications

Electronic and magnetic structures of EuB6: The effects of pressure and doping

Electronic and magnetic structures of EuB6: The effects of pressure and doping

Evidence for a subtle structural symmetry breaking in EuB₆

Multiple-Structure Optical Spectral Weight Transfer in Ferromagnetic EuB6

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Magnetic properties in Ca-doped Eu hexaborides

Cited by 13 publications

References 13 publications

Electronic and magnetic structures of EuB6: The effects of pressure and doping

Electronic and magnetic structures of EuB6: The effects of pressure and doping

Evidence for a subtle structural symmetry breaking in EuB6

Multiple-Structure Optical Spectral Weight Transfer in Ferromagnetic EuB6

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Product

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Evidence for a subtle structural symmetry breaking in EuB₆