Ti, Mn, Cr 2p-3d resonant photoemission for compounds with substitution of Ti atoms of host lattice by the Cr atoms CrxTi1-xSe2 and for compounds with intercalation of Mn and Cr atoms MnxTiSe2, CrxTiTe2 is studied. It is shown that the resonant behaviour depends on the geometry of survey, on 3d metal atoms lattice positions and on the magnitude and localization of atomic magnetic moment. © Published under licence by IOP Publishing Ltd

Kuznetsov, M. V.

Merentsov, A. I.

Shkvarin, A. S.

Titov, A. N.

Yablonskikh, M. V.

Yarmoshenko, Y. M.

Journal of Physics Conference Series

English

Institutional repository of Ural Federal University named after the first President of Russia B.N.Yeltsin

Journal of Physics: Conference SeriesObserving of Ti, Cr and Mn 2p-3d resonance invalence band of titanium dichalcogenidesTo cite this article: M V Yablonskikh et al 2013 J. Phys.: Conf. Ser. 425 102004 View the article online for updates and enhancements.Related contentResonant photoemission at the L3absorption edge of Mn and Ti and theelectronic structure of 1T-Mn0.2TiSe2M V Yablonskikh, A S Shkvarin, Y MYarmoshenko et al.-Ferromagnetism and structuraltransformations caused by Cr intercalationintoTiTe2N V Baranov, V G Pleshchev, N VSelezneva et al.-The experimental band structure ofoccupied and unoccupied states oftitanium dichalcogenidesW Drube, I Schafer and M Skibowski-This content was downloaded from IP address 213.142.35.54 on 20/07/2019 at 08:54      Observing of Ti, Cr and Mn 2p-3d resonance in valence band of titanium dichalcogenides  M.V.Yablonskikhb, A.S.Shkvarina,c, Yu.M.Yarmoshenkoa, A.I.Merentsova,c, M.V.Kuznetsovd,c, A.N.Titova,c aInstitute of Metal Physics, Russian Academy of Sciences-Ural Division, 620990 Ekaterinburg, Russia bSincrotrone Trieste SCpA, Basovizza I-34012, Italy cUral Federal University, 620083, Ekaterinburg, Russia dInstitute of Solid State Chemistry, Russian Academy of Sciences – Ural Division, 620990, Ekaterinburg, Russia shkvarin@ifmlrs.uran.ru Abstract. Ti, Mn, Cr 2p-3d resonant photoemission for compounds with substitution of Ti atoms of host lattice by the Cr atoms CrxTi1-xSe2 and for compounds with intercalation of Mn and Cr atoms MnxTiSe2, CrxTiTe2 is studied. It is shown that the resonant behaviour depends on the geometry of survey, on 3d metal atoms lattice positions and on the magnitude and localization of atomic magnetic moment. 1.  Introduction Titanium dichalcogenides and their derivatives - intercalation compounds TMxTiX2 (TM-transition metal, X-chalcogen) and substitution compounds TMxTi1-xX2 are natural analogues of artificial layered structures with the possible spin polarization at the Fermi level. The degree of spin polarization is associated with the effective magnetic moment of the intercalated metal [1]. The effective magnetic moment depends on the method of doping - substitution or intercalation. The reason for this dependence is a covalent bond between the TM and the lattice, leading to the hybridization TM3d/Ti3d - states. In the case of substitution this hybridization is absent due to the geometrical reasons, therefore the degree of spin polarization is higher. On the other hand, the degree of spin polarization of the charge carriers, which has important practical value, is determined by the position of TM3d/Ti3d - states in relation to the Fermi level. RPES is able to give information about the position of TM3d/Ti3d - band relative to the Fermi level and the localization of the electrons in the Brillouin zone. The angular dependence of photoemission, which is detected even at relatively high excitation energy and high crystal symmetry, is often observed in single-crystal samples. This dependence is highly pronounced in the resonant photoemission of two-dimensional titanium dichalcogenides single crystals [2, 3]. The angular dependence is easily observed in the vicinity of high-symmetry points of the Brillouin zone for the 2p edges of Ti, Cr and Mn where the excitation energy is relatively small (from 11th International Conference on Synchrotron Radiation Instrumentation (SRI 2012) IOP PublishingJournal of Physics: Conference Series 425 (2013) 102004 doi:10.1088/1742-6596/425/10/102004Published under licence by IOP Publishing Ltd 1      460 eV to 640 eV, respectively). In the setup used in these experiments a polar angle range is within 3.5, therefore, the projection of the wave vector kII is smaller than the size of a typical Brillouin zone in the titanium dichalcogenides (1 Ǻ-1). For the investigated samples the change of the polar angle in the highly-symmetric direction -M, K is within the range from the maximal MAX=5.5 to minimal MIN=4 for Ti 2p and Mn 2p excitations, correspondingly.  The Ti 3d and chalcogen np electronic states create strong bands symmetrical relative to the Г point. Additionally, 3d states of intercalated TM create bands symmetrical relative to the M point of the Brillouin zone [4]. The electronic states of the intercalated TM form bands just below the Fermi level which are delocalized and blurred over the Brillouin zone [3].  In this situation, the 2p-3d TM resonance in the valence band spectra is usually diffused over the intense chalcogen contribution, in contrast to the case of 2p-3d Ti for which 3d states are usually localized in the  of the Brillouin zone. 2.  Experiment.  Single crystals for the X-ray spectra measurements were grown by the gas transport reaction method in evacuated quartz ampoules with iodine as the gas carrier [5]. The single crystals had a shape of thin plates ≈ 2x3 mm large and ≈ 0.05 mm thick. X-ray resonance photoelectron and absorption spectra were measured using the standard setup of BACH [6] and CIPO [7] beamlines of the ELETTRA synchrotron. All measurements were performed at room temperature. To obtain a fresh surface, the crystals were cleaved in a working chamber at a pressure lower than 1x10-9 mbar. The binding energy scale was calibrated through the Au 4f7/2 binding energy and through the Fermi edge. The photoelectron analyzer resolution was set to 0.19 eV. The valence band spectra “at resonance” were obtained using excitation energy corresponding to the resonant excitation maximum (EMAX) [8]. At this energy the resonance behavior is observed as additional peaks in the valence band due to the existence of localized electrons under the Fermi level [8]. The spectra labeled as “Before resonance” and “After resonance” was obtained using excitation energies at approximately 10 eV lower and 10 eV higher from EMAX respectively. 3.  Results and discussion. Resonant photoemission spectra for Cr0.2Ti0.87Se2 and Cr0.78Ti0.36Se2 substitution compounds and for MnxTiSe2, Cr0.5TiTe2 intercalation compounds are investigated. In intercalated compound MnxTiSe2 intense Ti 2p-3d resonance behavior is observed (fig.1.). In intercalated compound Cr0.5TiTe2 a resonance peak is also detected. It is established that in host TiTe2 resonant Ti 3d band is caused by the increasing occupancy of Ti 3d band compared with TiSe2 and TiS2 [9]. In the Cr0.5TiTe2 Ti 2p-3d resonance behavior is almost absent if we consider the contribution to the resonance due to the effect of increasing occupancy of Ti 3d band in titanium ditelluride [9]. When compared with MnxTiSe2, the intensity of resonance peak in Cr0.5TiTe2 is low though the Cr0.5TiTe2 and MnxTiSe2 have an identical crystal structure. Likely, this effect indicates that the degree of charge transfer in Cr0.5TiTe2 is lower that for Mn0.2TiSe2 since a covalent contribution to the chemical bond between Cr and Ti is higher than that between Mn and Ti in MnxTiSe2 in which the chemical bond is partially ionic [3]. In TiSe2 and substitution compound CrxTi1-xSe2 the Ti 2p-3d resonance behavior is not observed (fig.1.). It means that the Ti 3d states do not form a narrow localized band just below the Fermi energy [9].  11th International Conference on Synchrotron Radiation Instrumentation (SRI 2012) IOP PublishingJournal of Physics: Conference Series 425 (2013) 102004 doi:10.1088/1742-6596/425/10/1020042      15 10 5 0 15 10 5 0Mn0.2TiSe2Cr0.78Ti0.36Se2Cr0.2Ti0.87Se2TiSe2Intensity, arb. units Intensity, arb. unitsEFSe4pBefore resonanceAt resonanceTiSe2Cr0.78Ti0.36Se2Cr0.2Ti0.87Se2Mn0.2TiSe2Se4p   RRASTi3dAfter resonanceCr0.78Ti0.36Se2Cr0.2Ti0.87Se2Mn0.2TiSe2TiSe2Se4pBinding energy, eVBinding energy, eV  Before resonanceTe5pEFCr0,5TiTe2  TiTe2At resonanceRRASCr0,5TiTe2TiTe2Te5p  After resonanceTe5pTiTe2Cr0,5TiTe2  Fig 1. Valence band spectra. Left panel: before, at and after Ti 2p-3d resonance (top to bottom) for intercalated compound Mn0.2TiSe2, for substitution compounds Cr0.2Ti0.87Se2, Cr0.78Ti0.36Se2 and pristine TiSe2. Right panel: before, on and after Ti 2p-3d resonance (top to bottom) for intercalated compound Cr0.5TiTe2 and pristine TiTe2. 15 10 5 0 15 10 5 0Te5pCr0.5TiTe2Cr0.78Ti0.36Se2Cr0.2Ti0.87Se2Intensity, arb. units Intensity, arb. unitsEFSe4pBefore Cr 2p-3d resonanceTe5pCr0.5TiTe2At Cr 2p-3d resonanceCr0.78Ti0.36Se2Cr0.2Ti0.87Se2Se4p   RRASCr3dTe5pCr0.5TiTe2After Cr 2p-3d resonanceCr0.78Ti0.36Se2Cr0.2Ti0.87Se2Se4pBinding energy, eVBinding energy, eV  Before Mn 2p-3d resonanceSe4pEFMn0,2TiSe2  Mn0,2TiSe2At Mn 2p-3d resonanceRRASSe4p  Mn0,2TiSe2After Mn 2p-3d resonanceSe4p  Fig 2. Valence band spectra. Left panel: before, at and after Cr 2p-3d resonance (top to bottom) for substitution compounds Cr0.2Ti0.87Se2, Cr0.78Ti0.36Se2 and intercalated compound Cr0.5TiTe2. Right panel: before, at and after Mn 2p-3d resonance (top to bottom) for intercalated compound Mn0.2TiTe2.  11th International Conference on Synchrotron Radiation Instrumentation (SRI 2012) IOP PublishingJournal of Physics: Conference Series 425 (2013) 102004 doi:10.1088/1742-6596/425/10/1020043      From the spectra in fig.2 follows that for the transition metal 2p-3d resonance behavior is observed for substitution compounds, while for intercalation compounds the resonance behavior is weak and almost invisible. For MnxTiSe2 the presence of a strong Ti resonance and of a weak Mn resonance indicates that the Pauli contribution to the magnetic susceptibility is caused by the Ti 3d electrons, but not by the Mn 3d electrons. For Cr0.5TiTe2 both chromium and titanium resonances are weak due to the suppression of magnetic moments. This suppression is a result of formed covalent bonds between the Ti and Cr atoms. In CrxTi1-xSe2 resonant behavior is caused by the Cr 3d electrons, which possess a magnetic moment, localized under the Fermi level [2]. The weak resonance in chromium and manganese intercalation compounds has two reasons. The first is the survey geometry, and the second is the delocalization of electron states in the Brillouin zone, which leads to the suppression of the atomic magnetic moment. The experimental conditions used, where the c axis of the single crystal is coincident with that of the focal axis of the analyzer, are favorable for the observation of photoelectrons corresponding to the states localized in the vicinity of the Brillouin zone  point. For the substitution compounds the main contribution is made in the vicinity of the Г point by both Ti 3d and the Cr 3d states. For the intercalation compounds the main contribution in the vicinity of the Г point is also made by Ti 3d states in contrast to the 3d states of the intercalated ion of 3d-metals [4]. It allows detecting the resonance Ti 2p-3d behavior in Cr0.5TiTe2 and Mn0.2TiSe2, but the Cr 2p-3d and Mn 2p-3d resonance behavior in these compounds is not observed. 4.  Conclusion. The resonance behavior of 3d states of Cr, Mn and Ti has been studied in the two-dimensional titanium dichalcogenides CrxTi1-xSe2, MnxTiSe2 and CrxTiTe2. The presence of the resonance behavior depends on the 3d metal atoms crystallographic positions. When titanium and chromium atoms occupy the regular lattice positions a significant resonant behavior of the Ti 3d and Cr 3d states is detected. A resonant behavior was weak for the 3d states of the intercalated Mn and Cr. The magnitude of the resonance peak depends on the degree of localization of the magnetic moment on the atom. Resonant photoemission allows one to determine which electrons of which atom contribute to the magnetic properties of the investigated compound. This value is well correlated with the magnitude of effective magnetic moments obtained from the measurement of magnetic susceptibility. The confirmation of the same degree of spin polarization could be obtained from the magnetoresistance experiment. 5.  Acknowledgments. Work is supported by the Presidium RAS, project 12-P-2-1051 and RFBR project 10-03-6047 ural. Work on synchrotron ELETTRA supported by International Centre for Theoretical Physics (ICTP), projects N20100397 and N20105305. References [1] Titov A.N. 2004 46 PSS 1681 [2] Shkvarin A.S. et al. 2011 JETP 112 87 [3] Yablonskikh M.V. et al. 2012 Journal of Physics: Condensed Matter 24 45504 [4] Kuznetsova T.V. et al. 2005 Phys. Rev. B: Condens. Matter 72, 085418 [5] Shkvarin A.S. et al. Journal of Physics and Chemistry of Solids 2012 73 1562 [6] Zangrando M. et al.2001 Rev. Sci. Instrum. 72 1313–9 [7] Derossi A. et al. 1995 Rev. Sci. Instrum., 66 1718 [8] Hüfner S. et al.2000 Phys. Rev. B: Condens. Matter 61, 12582 [9] Shkvarin A.S. et al. 2012 JETP 115 798 11th International Conference on Synchrotron Radiation Instrumentation (SRI 2012) IOP PublishingJournal of Physics: Conference Series 425 (2013) 102004 doi:10.1088/1742-6596/425/10/1020044

Observing of Ti, Cr and Mn 2p-3d resonance in valence band of titanium dichalcogenides

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Observing of Ti, Cr and Mn 2p-3d resonance in valence band of titanium dichalcogenides

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