Pressure-induced spin transition and site-selective metallization in cocl2

ABSTRACT The interplay between spin states and metallization in compressed CoCl2 is investigated by combining diffraction, resistivity and spectroscopy techniques under high-pressure

conditions and _ab-initio_ calculations. A pressure-induced metallization along with a Co2+ high-spin (S = 3/2) to low-spin (S = 1/2) crossover transition is observed at high pressure near

70 GPa. This metallization process, which is associated with the _p_-_d_ charge-transfer band gap closure, maintains the localization of 3_d_ electrons around Co2+, demonstrating that

metallization and localized Co2+ -3_d_ low-spin magnetism can coexist prior to the full 3_d_-electron delocalization (Mott-Hubbard _d-d_ breakdown) at pressures greater than 180 GPa. SIMILAR

CONTENT BEING VIEWED BY OTHERS BAND GAP CROSSOVER AND INSULATOR–METAL TRANSITION IN THE COMPRESSED LAYERED CRPS4 Article Open access 18 August 2020 INSULATOR–METAL TRANSITION IN CRSITE3

TRIGGERED BY STRUCTURAL DISTORTION UNDER PRESSURE Article Open access 07 April 2023 CONTINUOUS CONTROL OF CLASSICAL-QUANTUM CROSSOVER BY EXTERNAL HIGH PRESSURE IN THE COUPLED CHAIN COMPOUND

CSCUCL3 Article Open access 12 July 2021 INTRODUCTION Pressure-induced structural phenomena have received considerable attention in transition-metal (_M_) dihalides and oxides _MX_2 (_X_:

Cl, Br, F, O) due to their ample and subtle polymorphism1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20 and their intriguing electronic properties associated with changes of metal

coordination, spin state, and/or insulator-metal transition. Most _MX_2 are antiferromagnetic Mott insulators21 that present strong _d-d_ electron-electron correlation22. The breakdown of

the Mott-Hubbard _d-d_ or charge-transfer _d-p_ electron correlation leading to a metallization, concurrent with a collapse of magnetism via electron delocalization, is the typical

pressure-induced electronic/magnetic behavior. These phenomena involve external pressures that induce a large crystal-field strength at _M_, causing the high-spin to low-spin (HS-LS)

transition1,23,24,25. In fact, spin crossover (SCO) is often portrayed as a trigger for metallization either by volume collapse22,25, or as a result of the ground-state change from HS to

LS22,23,24. Nevertheless, the coupling between structure, spin state, and electron delocalization (Mott-Hubbard metal-insulator transition) governing the electronic properties in _MX_2

requires clarification. The access to both electronic ground and excited states via optical spectroscopy at high pressure, combined with the modelling of the electronic properties through

_ab initio_ calculations and precise crystal structure determination and resistivity measurements, can provide a definitive description of electronic phenomena in compressed _MX_2 systems.

Pressure-induced transformations in _MX_2 involve a large variety of energetically-equivalent dense structures, which are characterized either by an increase of the _M_ coordination

number11,20, or by stacking up dense _MX_2 layers keeping the metal coordination14,26, depending on the metal/ligand ionic radii ratio. Due to their simple structure, phase diagrams of

crystals in the _MX_2 family show common features regarding the coordination polyhedra and the stacking sequence. This distinct structural behavior has important implications in their

electronic properties, which are substantially modified upon compression. Besides, these studies of _MX_2 under pressure are of importance in geophysics to understand polymorphism in the

Earth’s interior, where SiO2 plays an important role27,28,29. CoCl2 is an attractive system for studying combined structural and electronic effects because the octahedral coordination of

Co2+ (3_d_7) is thought to be stable in a wide pressure range13,14,15,26,30, which enables us to exclude the physics coming from the coordination number changes. Besides, this system has a

relatively small energy difference between its HS and LS phases31, and the SCO of the system can be observed in a very  accessible pressure regime. Furthermore, it is the member of the

_M_Cl2 series (_M_: Cr, Mn, Fe, Co) where SCO is expected to take place at the lowest pressure. In addition, SCO phenomena involving transition-metal ions with 3_d_7 electronic configuration

are very scarce. Thus, this system can be a good model system to explore the various origins of SCO and to give answer to questions such as whether the pressure-induced LS states (_t_6_e_1

configuration) originate from large crystal-field effects enhanced by the Jahn-Teller effect associated with LS configuration, or from the metallization, which can be induced either by the

_p-d_ charge-transfer gap closure or breakdown of _d-d_ Mott-Hubbard correlation. Here we report on the stability of the Co2+ coordination under compression in CoCl2, and the relationship

between SCO, crystal structure, and metallization. In order to achieve these goals we perform a combined experimental and theoretical study using optical absorption, Raman spectroscopy,

X-ray diffraction (XRD) and resistivity under pressure, and first-principles Density Functional Theory (DFT) calculations. RESULTS The Co2+ (3_d_7) Tanabe-Sugano diagram describing the

electronic states’ energy in terms of the octahedral crystal field (in Racah parameter _B_ units, Fig. 1) shows that, for CoCl2 (_B_ ≈ 80 meV at 50 GPa15,30), the HS-LS (4T1, S = 3/2 → 2E, S

 = 1/2) transition should occur at Δ_SCO_ = 1.7 eV. Importantly, the LS state may be affected by a strong Jahn-Teller effect, providing an additional lattice relaxation energy which, in

principle, could reduce the SCO crystal-field strength triggering metallization at unexpectedly low pressure19,30. Alternatively, high pressure could, in turn, suppress the Jahn-Teller

distortion causing the HS-LS to occur at higher pressures than expected, or even disappear if CoCl2 transforms into a fluorite-type structure (_d_3-like Co2+)20. XRD shows that CoCl2

exhibits nearly-degenerate layered structures at ambient conditions. The CoCl2 pressure-induced phase transition sequence as determined experimentally with support of DFT calculations is

indicated in Fig. 1. The three represented layered structures are more stable than the rutile, cotunnite, and fluorite phases at all pressures up to 100 GPa. This result, which is confirmed

by both single-crystal and powder XRD experiments at high pressure, demonstrates the stability of the hexagonal layered structure of CoCl2 and thus the Co2+ sixfold coordination in a wide

pressure range (0–60 GPa), in a way similar to FeCl214 and MgCl226 and contrary to CoF210,20. The stability of the given CoCl2 structures, which involve the different packing sequence of

layers of face-sharing CoCl6 octahedra, is a consequence of the subtle competition of inter-layer van der Waals interactions. The CoCl2 equation-of-state can be phenomenologically described

by two Murnaghan’s equations: one above and one below 14 GPa (see Supplementary Figs S1–S3). Figure 2 shows the pressure dependence of the optical absorption spectra of CoCl2 around the

charge-transfer band gap (a) and in the sub-gap Co2+ _d-d_ crystal-field region (b). Besides the gap energy, these spectra allow us to determine the excited-state electronic structure in the

transparency window of CoCl2 (≈50 GPa). At ambient conditions, the main sub-gap absorption peaks within the _D_3_d_ (nearly _O__h_) CoCl64− octahedron7,8 correspond to crystal-field

transitions 4T1(F) → 4T2(F), 4A2(F), and 4T1(P) and are located at 0.79, 1.66 and 2.10 eV, respectively. In terms of the Tanabe-Sugano diagram for _d_7 ions (Fig. 1b)32,33, the transition

energies at ambient pressure correspond to Δ = 0.87 eV and _B_ = 97 meV with Δ/_B_ = 9.0 (see Supplementary Table S1)15,30,32. According to this diagram the crystal-field strength required

to induce the SCO is (Δ/_B_)_SCO_ = 21. Interestingly, the SCO also involves crossing of the 4T2(F) and 2T1(G) excited states, hence these states, which are well observed by optical

absorption, can be used to efficiently probe the HS-LS transition. The variation of the absorption spectra with pressure shows that the band gap energy decreases linearly with pressure at a

rate of −43 meV/GPa (Fig. 3). Such a large shift is responsible for the intense piezochromism exhibited by CoCl2 (Fig. 2a). The pressure-induced redshift of the bandgap follows a quadratic

dependence with the crystal volume yielding gap closure at _V_ = 17.5 Å3/Co (_V_/_V_0 = 0.56) – i.e. 80 GPa– (see Supplementary Fig. S5(c)). This redshift is produced by the hybridization

enhancement of the Cl−-_p_ and Co2+-_d_ orbitals with pressure which in turn causes a broadening of the mainly 3_p_- and 3_d_-orbital valence band and an energy decrease of the mainly

3_d_-orbital intermediate band both reducing the _p-d_ charge-transfer bandgap. DFT reproduces the decrease in the band gap of HS state (_P_ < 67 GPa) reasonably well (see Supplementary

Fig. 6(c)). The plots of the electron band and density of states certainly show a clear energy delocalization of the _d_-orbital manifolds with pressure yielding band broadening (see

Supplementary Fig. S7(c,d)). Concurrently, the increasing crystal-field energy as obtained from the optical spectra, and the reduction of _B_ from 97 to 82 meV in the 0–50 GPa range yield a

Δ/_B_ variation from 9.0 to 18.5, which implies an almost doubled splitting between _e_ and _t_2 orbitals, Δ, from 0.87 to 1.52 eV (see Supplementary Table S1 and Fig. S5). As Figs 2 and 3

show, the variation of the absorption spectrum and its associated peak energies with pressure reveal that Co2+ has a HS state in the crystal transparency range. However, extrapolating the

linear dependence of the transition energies with pressure we obtain a HS to LS [4T1(F) ↔ 2E(G)] transition at 67 GPa. It is worth noting that the SCO is observed in the DFT + U results

using a Coulomb correlation energy _U_ = 3 eV (Figs 3 and 4). As indicated in the Methods section, this method cannot capture the evolution of the Coulomb correlation parameter upon volume

changes and could underestimate the SCO pressure for high pressure regime31,34,35. However, the essence of the electronic and magnetic properties before and after the transition is valid.

The spectroscopic determination of the 3_d_-electron structure together with the DFT estimates make CoCl2 a reference system to validate theories dealing with SCO phenomena and metallization

processes in transition-metal systems25,36,37,38,39,40,41,42,43. Figure 3 plots the calculated magnetic moment as a function of pressure. According to DFT calculations, the Co2+ magnetic

moment abruptly decreases from HS, _μ__eff_ = 2.6 _μ__B_, to LS, _μ__eff_ = 0.9 _μ__B_, at around 67 GPa with a hysteresis of 8 GPa. The experimental SCO pressure and the crystal and

electronic structures demonstrate that the Jahn-Teller coupling is not involved in the stabilization of the LS ground state, 2E. This contrasts with one of the hypotheses given

elsewhere30,31, that the high-pressure conditions required for SCO could be relaxed by the strong Jahn-Teller effect in the LS 2E state down to 35 GPa if we consider a Jahn-Teller coupling

similar to those measured in the CuCl6 system44. The lack of a HS-LS transition at ≈35 GPa in CoCl2 indicates that the Jahn-Teller effect is unable to distort the Co2+ environment in the

severe high-pressure conditions required for SCO. The pressure dependence of the optical gap, _E__GAP_, allows us to infer that the _p-d_ charge-transfer gap closure (metallization) takes

place at 80 GPa. This result is confirmed by electrical resistance measurements under pressure (inset of Fig. 3 and Supplementary Fig. S12). Its pressure dependence _R_(_P_) unveils two

distinct regions corresponding to HS and LS states. The associated SCO pressure, _P__SCO_ = 70 GPa, is close to that derived from optical absorption. Interestingly, the progressive decrease

of _R_(_P_) in LS shows a change of slope for _P_ > 80 GPa indicating the metallization onset. Spin density- and DOS simulations indicate that the charges are mainly localized at the Co2+

site and small _p-d_ hybridized ones can be observed at Cl− sites for HS. For _P_ > 67 GPa (LS) a progressive decrease of the localized charges at Co2+ occurs due to hybridization

increase. However, the hybridized spin density spreads out over the entire crystal for _P_ > 80 GPa (_E__GAP_ = 0) in the Cl− plane, while it is strongly localized at Co2+, indicating

that metallization mainly involves Cl− sublattices rather than the Co2+ ones. Furthermore, a full electron delocalization is completed for _P_ > 180 GPa (Fig. 4). This result is

noteworthy since it correlates two distinct electronic features: (1) the insulator-to-metal transition involves _p-d_ charge-transfer states and can be induced under compression in close

proximity right after the HS-LS transition; (2) Mott-Hubbard _d-d_ electron breakdown should occur for _P_ > 180 GPa. Thus, 3_d_(_e_)-electrons still keep their local character at the

band-gap closure, albeit pressure-induced progressive delocalization occurs within LS ground state up to approximately 180 GPa, at which delocalization process is completed (Figs 3 and 4).

CONCLUSIONS In summary, with various types of experimental and theoretical approaches, we have thoroughly analysed the physics of the pressure-induced spin-state transition and metallization

phenomena in CoCl2. We have shown that the layered structure of CoCl2, and hence the Co2+ sixfold coordination, is stable in the 0–200 GPa range, in contrast to CoF2, whose high-pressure

phases involve increasing coordination numbers (6 → 8 → 9). We demonstrate that pressure-induced metallization is associated with _p-d_ charge-transfer band gap, closing at about 80 GPa.

Although the HS-to-LS transition (67 GPa) can trigger insulator-to-metal transition, DFT calculations also show that after the SCO metallization Co2+ preserves the local character of the

3_d_-electrons and that Mott-Hubbard-electron breakdown takes place for _P_ > 180 GPa in LS. In consequence, this work demonstrates that metallization with involvement of Cl− planes and

localized Co2+-3_d_ LS magnetism can coexist prior to Mott-Hubbard breakdown in CoCl2. These results unveil the complex metallization mechanism of CoCl2 under compression with Cl− and Co2+

layers exhibiting site-dependent electrical and magnetic behaviours. Especially, the intermediate phase with metallic magnetism is rarely observed in a system with local moment such as

transition metal complexes. We believe these findings provide new insight into unforeseen electronic properties of multilayer 2D systems and highlight the importance of high-pressure studies

as a route to novel electronic and magnetic phases. METHODS CRYSTAL STRUCTURE: X-RAY DIFFRACTION Both single-crystal plates (100 × 80 × 30 _μ_m3) and powder of CoCl2 (Merck) were used for

high-pressure experiments. CoCl2 crystallizes in the trigonal space group _R3m_ at ambient conditions45. The evolution of the crystal structure with pressure was studied by x-ray diffraction

(XRD) using the I15 beam station at the DIAMOND synchrotron under proposals 832, 1655 and 6078. The pressure was applied by means of Almax-Boehler and MALTA-type Diamond Anvil Cell (DAC).

DACs were loaded with several Ruby spheres (10 _μ_m diameter) as pressure gauge46 using helium, silicone oil and paraffin as pressure transmitting media for powder and single crystal XRD

experiments (see Supplementary Figs S1–S3). OPTICAL ABSORPTION AND RAMAN SPECTROSCOPY Optical absorption and Raman experiments were performed on single-crystal plates (100 × 80 × 35 _μ_m3)

of CoCl2. The optical spectroscopy experiments were carried out in membrane and Almax-Boehler DACs. 200-_μ_ m-thick Inconel 625 gaskets were preindented to 40 _μ_m. 170-_μ_ m-diameter holes

were perforated with a BETSA motorized electrical discharge machine. The DAC was loaded with a CoCl2 single crystal and ruby microspheres (10 _μ_m diameter) as pressure probes46 using

silicone oil as pressure-transmitting medium in an argon atmosphere inside a globe box to avoid sample hydration. Optical absorption under high-pressure conditions was performed on a

prototype fiber-optics microscope equipped with two 20× reflecting objectives mounted on two independent x -y -z translational stages for the microfocus beam, and the collector objective and

a third independent x -y -z translational stage for the DAC holder (Fig. 5). Optical absorption data and images were obtained simultaneously with the same device. Spectra in the UV-VIS and

NIR were recorded with Ocean Optics USB 2000 and NIRQUEST 512 monochromators using Si- and InGaAs-CCD detectors, respectively. Unpolarized micro-Raman scattering measurements were performed

with a triple monochromator Horiba-Jobin-Yvon T64000 spectrometer in subtractive mode backscattering configuration, equipped with a Horiba Symphony liquid-nitrogen-cooled CCD detector. The

514.5-nm and 647-nm lines of a Coherent Innova 70 Ar+-Kr+ laser were focused on the sample with a 20× objective for micro-Raman, and the laser power was kept below 4 mW in order to avoid

heating effects. The laser spot was 20 _μ_m in diameter and the spectral resolution was better than 1 cm−1. The Raman technique was used to check the sample structure through the

characteristic first-order modes (A1_g_ and E_g_ in the trigonal _R_\(\overline{3}\)_m_ CdCl2-type phase)38 as well as to determine structural phase-transition pressures (see Supplementary

Figs S10 and S11 and Table S3). The Raman high-pressure experiments were performed on the same CoCl2 single crystals employed in the optical absorption measurements. ELECTRICAL MEASUREMENTS

AT HIGH PRESSURE The electrical resistance measurement under pressure up to 96 GPa was performed using diamond anvil cell with solid transmitting medium NaCl (diamond’s culet diameter of 100

 _μ_m). Gasket consists of T301 and the insulate layer is cBN. Pressure was determined by ruby fluorescence method at low pressure and the shift of diamond’s Raman peaks. Figure 6 shows a

schematic view of the DAC. FIRST-PRINCIPLES THEORETICAL CALCULATIONS DENSITY FUNCTIONAL THEORY: CRYSTAL STRUCTURE AND PHASE TRANSITION For the description of an accurate phase transition, we

have performed total-energy calculations within the framework of dispersion-corrected Density-Functional Theory in the Projector Augmented Wave (PAW) and plane-waves (PW) formulation. The

Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional was employed coupled with the exchange-hole dipole moment (XDM) model dispersion correction (damping function parameters a1 = 

0.0000 and a2 = 3.8036 Å) as implemented in Quantum ESPRESSO. The calculation parameters are: 6 × 6 × 6 Monkhorst-Pack k-point grid, 60 Ry plane-wave cutoff energy, 600 Ry density-cutoff

energy and cold smearing with a smearing parameter of 0.05 Ry. Based on previous studies, we considered the following phases of CoCl2: cotunnite (_Pnma_, orthorhombic, Z = 4), CaCl2

(deformed rutile structure, _Pnnm_, orthorhombic, Z = 2), fluorite (_Fm_\(\overline{3}\) _m_, cubic, Z = 1), CoCl2 (_R_\(\overline{3}\) _m_, rhombohedral, ABCABC stacking), CdI2 (_P6_3 _mc_,

hexagonal, ABAB stacking), _ω_-phase (_P_\(\overline{3}\) _m1_, hexagonal, AAA stacking). All CoCl2 phases were calculated in a range of volumes encompassing the 0–100 GPa range and the

internal degrees of freedom (atomic positions and cell shape) were relaxed at each volume. DENSITY FUNCTIONAL THEORY: SPIN CROSSOVER AND METALLIZATION After clarifying structural phase

transitions, we identified that the electronic and magnetic transitions occur in _P_\(\overline{3}\) _m1_ phase. Thus, employing the same symmetry, we investigated the SCO behaviors in

detail. We further performed electronic-structure calculations within DFT + U scheme as implemented in Vienna Ab Initio Simulation Package (VASP)47. As for layered system, where the van der

Waals interactions are important, frequently used generalized gradient approximation (GGA) functionals sometimes fails to predict the correct structural behaviors. We found van der

Waals-corrected functions gives better description of the ground state volume such that the errors were 1.6% for many-body dispersion and 2.2% for Tkatchenko-Scheffler methods while D3

approach severely underestimates the volume by 8.2%31,34,35). From GGA48, we found that PBEsol overperforms PBE (3.8% vs. 8.1%) with accuracy similar to van der Waals approach, which enables

us to choose PBEsol scheme with safety. Note that in our previous reports, PBEsol successfully explained the spin-state transition behaviors for CoCl231. We also carefully tested various U

parameters and found that _U__eff_ = 3.0 eV fits best in describing the experimental transition behaviors. To obtain the pressure evolution of the electronic structure and magnetic

properties, we fully relaxed the atomic positions until the atomic forces are less than 0.001 eV/Å for each volume point. Once the transition volume is found, we have cross-checked the

results employing full potential full relativistic code FPLO49, and further analyzed its partial density of states (see Supplementary Figs S6–S9). DATA AVAILABILITY All data generated or

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Article  ADS  CAS  Google Scholar  Download references ACKNOWLEDGEMENTS Financial support from the Spanish Ministerio de Economıa y Competitividad (Project No. MAT2015-69508-P,

MAT2016-80438-P) and MALTA-CONSOLIDER (Ref. No. MAT2015-71070-REDC) is acknowledged. This work was also supported by the NRF Grant (Contracts No. 2016R1D1A1B02008461, No.

2017M2A2A6A01071297, No. 2018R1D1A1A02086051), Max-Plank POSTECH/KOREA Research Initiative (Grant No. 2016K1A4A4A01922028). XRD experiments were performed at I15 beamline at DIAMOND

Synchrotron Light Facility (Proposals Nos. 832, 1655 and 6078). We also acknowledge the computing time provided by Red Española de Supercomputación (RES), TACC-Texas Supercomputer Center,

and MALTA-Cluster. CQJ is grateful to National Science Foundation & Ministry of Science & Technology of China for the support. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS *

Universidad de Cantabria, MALTA Consolider Team - DCITIMAC, Santander, 39005, Spain Jose A. Barreda-Argüeso, Fernando Aguado, Ignacio Hernández, Jesús González & Fernando Rodríguez *

Synchrotron SOLEIL, L’Orme des Merisiers, St Aubin BP48, 91192, Gif-sur-Yvette cedex, France Lucie Nataf * Universidad de Oviedo, Departamento de Química Física y Analítica, Oviedo, 33006,

Spain Alberto Otero-de-la-Roza & Víctor Luaña * Institute of Physics, Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing, 100190, China Yating

Jia & Changqing Jin * Pohang University of Science and Technology, Department of Physics, PCTP, Pohang, 37673, Korea Bongjae Kim & Byung I. Min * Kunsan National University,

Department of Physics, Gunsan, 54150, Korea Bongjae Kim * Pohang University of Science and Technology, Max Planck POSTECH/Hsinchu Center for Complex Phase Materials, Pohang, 37673, Korea

Kyoo Kim * Diamond Light Source Ltd, Chilton, Didcot, Oxfordshire, OX11 0DE, United Kingdom Wilhem Heribert * Okayama University, Institute for Planetary Materials, Yamada 827, Misasa,

Tohaku, Tottori, 682-0193, Japan Andrew P. Jephcoat Authors * Jose A. Barreda-Argüeso View author publications You can also search for this author inPubMed Google Scholar * Lucie Nataf View

author publications You can also search for this author inPubMed Google Scholar * Fernando Aguado View author publications You can also search for this author inPubMed Google Scholar *

Ignacio Hernández View author publications You can also search for this author inPubMed Google Scholar * Jesús González View author publications You can also search for this author inPubMed 

Google Scholar * Alberto Otero-de-la-Roza View author publications You can also search for this author inPubMed Google Scholar * Víctor Luaña View author publications You can also search for

this author inPubMed Google Scholar * Yating Jia View author publications You can also search for this author inPubMed Google Scholar * Changqing Jin View author publications You can also

search for this author inPubMed Google Scholar * Bongjae Kim View author publications You can also search for this author inPubMed Google Scholar * Kyoo Kim View author publications You can

also search for this author inPubMed Google Scholar * Byung I. Min View author publications You can also search for this author inPubMed Google Scholar * Wilhem Heribert View author

publications You can also search for this author inPubMed Google Scholar * Andrew P. Jephcoat View author publications You can also search for this author inPubMed Google Scholar * Fernando

Rodríguez View author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS All authors reviewed the manuscript. F.R. participated in all parts of the

project. J.A.B.-A. and I.H. did the optical absorption and J.G. the Raman spectra as a function of pressure. L.N., I.H., W.H. and A.J. conducted the x-ray diffraction measurements and F.A.

collected diffraction data and helped with structure refinement. A.O.R. and V.L. did the DFT calculations for structural refinement and phase transitions, and B.K., K.K. and B.I.M. performed

the DFT + U electronic structure calculations for spin crossover and metallization processes. Y.J. and C.J. did the electrical measurements at high pressure. All authors participated in the

analysis of data and revised the manuscript. CORRESPONDING AUTHOR Correspondence to Fernando Rodríguez. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing interests.

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CITE THIS ARTICLE Barreda-Argüeso, J.A., Nataf, L., Aguado, F. _et al._ Pressure-induced spin transition and site-selective metallization in CoCl2. _Sci Rep_ 9, 5448 (2019).

https://doi.org/10.1038/s41598-019-41337-4 Download citation * Received: 30 October 2018 * Accepted: 07 March 2019 * Published: 01 April 2019 * DOI:

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