X-ray absorption and magnetic circular dichroism of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>LaCoO</mml:mtext></mml:mrow><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>,<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>La</mml:mtext></mml:mrow><mml:mrow><mml:mn>0.7</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mtext>Ce</mml:mtext></mml:mrow><mml:mrow><mml:mn

Merz, Michael; Nagel, Peter; Pinta, C.; Samartsev, A.; Löhneysen, H. v.; Wissinger, M.; Uebe, S.; Aßmann, Andrea; Fuchs, D.; Schuppler, S.

doi:10.1103/physrevb.82.174416

Cited by 110 publications

(67 citation statements)

References 56 publications

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“…The Rietveld refined parameters from the XRD data of LaCo1−xNbxO3 (x = 0 -0.2) are summarized along with the pseudocubic (pc) lattice parameters and unit cell volume. sample [44], which could be due to the superexchange interaction between Co 3+ -Co 3+ ions [62][63][64]. Interestingly, the M S value is significantly higher (600 emu/mole) even with 2.5% Nb substitution, which further increased with increasing Nb concentration up to 10% (i.e.…”

Section: Resultsmentioning

confidence: 95%

Anomalous magnetic and spin glass behavior in Nb-substituted LaCo1−xNbxO3

Shukla

Dhaka

2018

Phys. Rev. B

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We report the structural, magnetic, transport and electronic properties of Nb substituted LaCo1−xNbxO3 (x = 0-0.2). The Rietveld analysis of x-ray diffraction data demonstrate structural phase transitions from rhombohedral to orthorhombic and further to monoclinic with increasing the Nb concentration up to x ≥ 0.2. Interestingly, we observed dramatic changes in the magnetization (M) with increasing the Nb concentration, as the M sharply increases below 10 K even at 2.5% substitution. Furthermore, ac susceptibility data show the spin-glass behavior in x = 0.1 sample. We find that the density of states near the Fermi level decreases and the activation energy increases, which results in the decreasing conductivity with higher Nb concentration. A significant shift in the peak position of A2g phonon mode has been observed using Raman spectroscopy, which indicates the change in the coupling due to the structural distortion with Nb substitution. The core-level photoemission study confirms that the Nb is present in 5+ valence state. Our study reveals that the nonmagnetic Nb 5+ (d 0 ) substitution converts Co 3+ ions to Co 2+ and stabilize both in the high-spin state. Our results suggest that structural and spin-state transitions as well as the difference in the ionic radii between Nb 5+ and Co 3+ are playing an important role in tuning the physical properties.

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Section: Resultsmentioning

confidence: 95%

Anomalous magnetic and spin glass behavior in Nb-substituted LaCo1−xNbxO3

Shukla

Dhaka

2018

Phys. Rev. B

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“…We show that beyond a tensile strain of 2.5%, LCO undergoes a spin state transition from LS to mixed HS/LS states [13], and also explain why the higher concentration of HS Co 3+ is preferred in tensile-strained LCO [6]. This feature of our theory is due to a reduced mixing between the Co 3d and O 2p states in the HS CoO 6 units, leading to softer HS Co-O bonds, compared to that of the LS CoO 6 units [14].…”

Section: Introductionmentioning

confidence: 99%

“…In addition to transport measurements showing insulating behavior for tensile-strained FM LCO [7], Fuchs and co-workers have also shown that both the population of higher spin states and the magnetization in LCO increase as tensile strain increases [6]. Using X-ray techniques, Merz and coworkers have suggested that the magnetic structure of tensile-strained LCO grown on SrTiO 3 (STO) is a mixture of Co 3+ high spin (HS) and Co 3+ LS states [13]. A recent report by Metha et al also suggests that compressive strain by itself cannot produce a FM state in LCO [12], indicating the existence of an asymmetric orbital-lattice interaction [4].…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, strain engineering in these oxide heterostructures opens up routes for creating novel electronic phases [2][3][4]. An exciting example is the recent demonstration of biaxial tensile strain stabilizing an insulating ferromagnetic (FM) ground state in LaCoO 3 (LCO) [5][6][7][8][9][10][11][12][13][14]. Though LCO is a classic example of a correlated 3d transition metal perovskite oxide [15,16], FM correlation has never been observed for the bulk ground state where the Co 3+ ions exist in the so-called low spin (LS) state (total spin per Co S=0) [15].…”

Section: Introductionmentioning

confidence: 99%

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Strain-driven spin-state transition and superexchange interaction in LaCoO3:Abinitiostudy

2012

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Using spin density functional theory with the Hubbard correction we investigate the magnetic structure of strained LaCoO 3 . We show that beyond biaxial tensile strain of 2.5%, local magnetic moments originating from the high spin (HS) state of Co 3+ emerge in a low spin (LS) Co 3+ matrix. In contrast, we find that compressive strain is not able to stabilize a magnetic state due to geometric constraints. LaCoO 3 accommodates tensile strain via spin state disproportionation resulting in an unusual sublattice structure. In tensile-strained LaCoO 3 , the first nearest neighbor (n.n.) exchange coupling is ferromagnetic (FM) while the second n.n. interaction is stronger and antiferromagnetic (AFM). This unusual feature of the exchange parameters is qualitatively verified with a model superexchange calculation. Due to the competition between the FM and AFM couplings in the system, we find that the most probable magnetic structure of tensile-strained LCO is a canted-spin structure, which may explain the relatively small observed magnetic moment of 0.7μ B /Co 3+ .

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“…This provides further evidence for the HS state of the Co ions in Sr 2 Co 0.5 Ir 0.5 O 4 . We would like to note that the XMCD spectrum of HS Co 3+ in octahedral symmetry has been rarely reported in literature: only in LaCoO 3 single crystal 10 and thin films 41,42 .…”

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confidence: 99%

Intricacies of the Co3+ spin state in Sr2Co0.5Ir0.5<

et al. 2017

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We report on a combined soft x-ray absorption and magnetic circular dichroism (XMCD) study at the Co-L3,2 on the hybrid 3d/5d solid state oxide Sr2Co0.5Ir0.5O4 with the K2NiF4 structure. Our data indicate unambiguously a pure high spin state (S = 2) for the Co 3+ (3d 6 ) ions with a significant unquenched orbital moment Lz/2Sz = 0.25 despite the sizeable elongation of the CoO6 octahedra. Using quantitative model calculations based on parameters consistent with our spectra, we have investigated the stability of this high spin state with respect to the competing low spin and intermediate spin states.PACS numbers: 71.70. Ch, 75.47.Lx, 78.70.Dm, 72.80.Ga Cobalt compounds have aroused a great deal of attention in the scientific community because of the complex and large diversity of physical phenomena displayed, including metal-insulating transitions 1-3 , superconductivity 4 , large magneto-resistance 5 and high thermoelectric power 6 . This richness of electronic and magnetic properties is closely related not only to the possibility of stabilizing cobalt in different valence states but also to its ability to present different spin states, the so-called spinstate degree of freedom 7,8 . For example, in an octahedral coordination, Co 3+ ions, which have the d 6 configuration, can exist in three possible spin states: a high spin (HS) state (S = 2, t 4 2g e 2 g ), a low spin (LS) state (S = 0, t 6 2g e 0 g ) and even an intermediate spin (IS) state (S = 1, t 5 2g e 1 g ) 7,9,10 . This spin state degree of freedom is evident in LaCoO 3 where the Co 3+ ions have a non-magnetic LS ground state and undergo a gradual transition with increasing temperature to a magnetic spin state [11][12][13] . The nature of the magnetic spin state (IS or HS) was heavily disputed in literature for over four decades, till an XMCD study clearly demonstrated it to be HS 10 . Calculations of the Co 3+ energy level diagram show that the LS (HS) state can be stabilized by a large (small) value of the crystal field 10Dq. The IS is always higher in energy for CoO 6 octahedra close to regular, like in LaCoO 3 10 .However, the IS state, with one electron in the e g states, is Jahn-Teller active and, hence, can gain energy and become the ground state in the presence of a sufficiently large distortion of the local structure 14 . For this reason the spin state of the Co 3+ ions in layered cobaltates, where the elongated distortion of the CoO 6 octahedra favors and may stabilize the IS state, have been subject of intense debate. In the case of layered La 2−x Sr x CoO 4 , contradicting scenarios for the Co 3+ ions were considered to interpret the complex structural, magnetic and transport properties of the system as a function of Sr doping: LS Co 3+ , IS Co 3+ 15-17 , HS-to-IS transition 18 , and mixing of HS/IS 19,20 . Only recently the spin state of Co 3+ in layered La 2−x Sr x CoO 4 was demonstrated by X-ray absorption spectroscopy (XAS) studies to be LS 21,22 for x = 0.5 and a mixture of LS/HS for x ≥ 1 22-24 . Band formation has been proposed to p...

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X-ray absorption and magnetic circular dichroism ofLaCoO3,La0.7Ce

Cited by 110 publications

References 56 publications

Anomalous magnetic and spin glass behavior in Nb-substituted LaCo1−xNbxO3

Anomalous magnetic and spin glass behavior in Nb-substituted LaCo1−xNbxO3

Strain-driven spin-state transition and superexchange interaction in LaCoO3:Abinitiostudy

Intricacies of the Co3+ spin state in Sr2Co0.5Ir0.5<

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