Nature of the Well Screened State in Hard X-Ray Mn2pCore-Level Photoemission Measurements ofLa1−x

Abstract

Using hard x-ray (HX; hν = 5.95 keV) synchrotron photoemission spectroscopy (PES), we study the intrinsic electronic structure of La1−xSrxMnO3 (LSMO) thin films. Comparison of Mn 2p corelevels with Soft x-ray (SX; hν ∼ 1000 eV) -PES shows a clear additional well-screened feature only in HX-PES. Take-off-angle dependent data indicate its bulk (≥ 20Å) character. The doping and temperature dependence track the ferromagnetism and metallicity of the LSMO series. Cluster model calculations including charge transfer from doping induced states show good agreement, confirming this picture of bulk properties reflected in Mn 2p core-levels using HX-PES.PACS numbers: 71.30.+h, 78.20.Bh Hole-doped manganese oxides with a perovskite structure of Re 1−x Ae x MnO 3 (Re and Ae being trivalent rare earth : Nd, Pr, Sm, etc. and divalent alkaline earth elements : Ca, Sr, Ba, respectively) exhibit a rich phase diagram originating in complex collective phenomena due to interplay among spin, charge, orbital, and lattice degrees of freedom [1,2]. Among the manganites, La 1−x Sr x MnO 3 (LSMO) is a prototypical series showing the largest one-electron bandwidth and accordingly, is less significantly affected by electron-lattice and Coulomb correlation effects [2]. The parent compound LaMnO 3 is an antiferromagnetic (AFM) insulator which becomes, on hole-doping induced by substitution of Sr for La, a ferromagnetic (FM) metal [3] exhibiting colossal magnetoresistance (CMR). The optimal doped compound (x = 0.4) exhibits the highest Curie temperature (T C ) of 360 K among manganites and a half-metallic nature [4]. Further hole-doping induces a magnetic transition, transforming the FM metal to an AFM metal phase for x > 0.5 [5]. In the case of thin films, the critical temperature and resistivity change slightly compared to the bulk materials due to the strain from the substrate, but the qualitative physical properties are similar to the bulk materials, provided the films are at least ∼ 10 unit cells (∼ 30Å) thick [6,7,8,9].In particular, high-quality bulk and thin films of the LSMO series do not exhibit charge order and are also free of micro-and nano-scale phase separation phenomena seen in the La-Ca, Nd-Sr and Pr-Sr manganites [2]. However, ultra thin films of LSMO (i.e. < 30Å or 10 unit cell thickness) are known to show a suppression of metallicity, ferromagnetic T C and magnetization [6,7]. In order to clarify the origin of these unusual physical properties, it is important to investigate the electronic structure of LSMO with a depth sensitive probe. Photoemission spectroscopy (PES) has long played a central role in studying the electronic structure of strongly correlated electron systems including manganese oxides [9,10,11,12,13,14]. Temperature dependent half-metallic ferromagnetism, charge and orbital ordering, and its connection with the electronic structure and colossal magnetoresistance of the manganites have been clarified [11,12,13]. Nevertheless, the change in the Mn 2p spectra of manganese oxides with hole doping is still not...

Empirical relationship between x-ray photoemission spectra and electrical conductivity in a colossal magnetoresistive manganite La1−xSrxMnO3

“…The spectra of x = 0.0 and 0.4 show very good agreement with those of thin films. 10 In addition to this agreement, one can find the shoulder structure S even at x = 0.8, for the first time. The systematic decrease in intensity and shift in energy of the shoulder S undoubtedly confirms that this feature corresponds to the Mn 3+ well-screened state.…”

“…Panel (a) shows that the distinct shoulder at 639-640 eV in Mn 2p 3/2 peak in HX-PES spectra is still observable in XPS spectra of x = 0.0 and 0.4 although the intensity is smaller due to lower bulk sensitivity. 10,12 Panel (b) shows the HX-PES spectra in the Mn 2p 3/2 region. The spectra of x = 0.0 and 0.4 show very good agreement with those of thin films.…”

“…A recent remarkable discovery in this field is the "metallic" peak/shoulder (hereafter shoulder, for simplicity) in the Mn 2p 3/2 corelevel spectra of LSMO thin films (0 ≤ x ≤ 0.55) measured by hard x-ray photoemission spectroscopy (HXa) t-hishida@mg.ngkntk.co.jp b) t-saitoh@rs.kagu.tus.ac.jp PES). 10 This shoulder structure is interpreted as the wellscreened peak of the Mn 3+ state and its intensity is considered to represent the metallicity of the system. 10 The shoulder intensity was even found to scale the conductivity in La 0.85 Ba 0.15 MnO 3 thin films.…”

“…10 This shoulder structure is interpreted as the wellscreened peak of the Mn 3+ state and its intensity is considered to represent the metallicity of the system. 10 The shoulder intensity was even found to scale the conductivity in La 0.85 Ba 0.15 MnO 3 thin films. 11 However, the full x dependence of the shoulder intensity and its relation to electrical conductivity was not resolved.…”

Nature of electron correlation and hybridization in NixCu1−xMnSb Heusler alloys

“…[14][15][16][17] This is due to the fact that during photoemission a 2p electron is emitted from Mn, leaving behind a hole in the core level. This sudden creation of a core-hole potential at the Mn site during photoexcitation initiates core hole screening which strongly depends on electron correlations and charge transfer (CT) processes.…”