Emergence of ferromagnetism and Jahn-Teller distortion in LaMn1−xCrxO3

Abstract

The emergence of a ferromagnetic component in LaM nO3 with low Cr-for-Mn substitution has been studied by x-ray absorption spectroscopy and x-ray magnetic circular dichroism at the Mn and Cr K edges. The local magnetic moment strength for the Mn and Cr are proportional to each other and follows the macroscopic magnetization. The net ferromagnetic components of Cr 3+ and M n 3+ are found antiferromagnetically coupled. Unlike hole doping by La site substitution, the inclusion of Cr 3+ ions up to x = 0.15 does not decrease the Jahn-Teller (JT) distortion and consequently does not significantly affect the orbital ordering. This demonstrates that the emergence of the ferromagnetism is not related to JT weakening and likely arises from a complex orbital mixing.PACS numbers: 78.70.Dm, 71.70.Ej, 75.30.Et Doped manganites have been extensively studied owing to their colossal magneto resistance property and its potential applications to magnetic devices. The substitution at the Mn site (B site in the ABO 3 perovskite formula) of various transitional metal elements dramatically modifies the magnetic and electronic properties. The variations of the magnetic and electronic behaviors are associated with the dissimilar 3d electron configuration of the substitutions. Cr doping at the Mn sites has attracted special attention because Cr 3+ ions have the same electronic configuration t 3 2g e 0 g as M n 4+ . As the Cr 3+ ionic radius (0.615Å) is much closer to that of M n 3+ high spin (0.645Å) than M n 4+ radius (0.530Å), low substitutions of Cr 3+ result in changing the M n 3+ density without large distortion of the crystal cell 1 . These features make the partial substitution of M n by Cr in LaM nO 3.00+δ an interesting system for studying the close relationship between Jahn Teller (JT) distortion, double exchange (DE) and superexchange (SE) interactions and orbital degeneracy. Since the first studies of the series LaM n 1−x Cr x O 3 in the 1950s 2,3 it is known that upon Cr-doping the antiferromagnetic (AFM) Mott insulator LaM nO 3 develops a ferromagnetic (FM) component, but the character of the M n 3+ − Cr 3+ interaction has been under debate for a long time 1,2,4-16 . A M n 3+ -Cr 3+ SE FM coupling may account for the increasing Curie temperature and spontaneous magnetization with increasing Cr doping 4-7 . On the other hand several groups proposed DE interaction between M n 3+ and Cr 3+ 1,7 . Cr dopants can also be viewed as a quenched random field 8,9 . However direct x-ray magnetic circular dichroism experiments suggest that the exchange interaction between M n 3+ and Cr 3+ leads to a net local antiparallel coupling 12-15 , regardless of the magnetic state nature of the manganite compound. This scenario is supported by spin resonance investigations 16 .As far as we know, unlike A site substitution, the local distortion in Cr-substituted systems has not been the object of a specific study. The usual view is that, in a similar way as the formal introduction of M n 4+ by A site doping and/or oxygen overstoichiometry, B s...

Enhancement of Double-Exchange Mechanism in Charge-Ordered Pr0.75Na0.25MnO3 Ceramics by Cr Doped at Mn-Site

“…In fact, it is in line with a previous report [15]. The DE mechanism between Mn 3+ ion and Cr 3+ ion has been suggested to be possible occurs in this study due to the Cr 3+ ion may have a similar role with Mn 4+ where the Cr 3+ (t 3 2ge 0 g) ion have same electronic configuration with Mn 4+ (t 3 2ge 0 g) ion [15,20]. Apart from that, the increasing of Cr content also influenced the intensity of the resistivity where this can be suggested to be due to the increase of carrier concentration as result of enhancement of the DE mechanism [15].…”

A cookbook for the investigation of coordination polymers by transition metal K-edge XMCD

“…Additionally, XMCD retains the chemical sensitivity of X-ray absorption spectroscopy (XAS), which is priceless when two or more TMs are present. Many kinds of compounds could thus be investigated and their properties better understood, for instance oxides (Subías et al, 2009;Ramos et al, 2009), alloys (Dartyge et al, 1995), magnetic multilayers (Pizzini et al, 1995), intermetallic compounds (Boada et al, 2010a), molecular magnets (Train et al, 2004) or Prussian blue analogs (PBAs) (Verdaguer et al, 1995(Verdaguer et al, , 1999Dujardin et al, 1998;Champion et al, 2001;Cafun et al, 2013;Lahiri et al, 2016). All these results were obtained thanks to worldwideavailable beamlines allowing for TM K-edge XMCD measurements, using either a scanning setup (Rogalev & Wilhelm, 2015;Haskel et al, 2007;Nakamura & Suzuki, 2013;Poldi et al, 2020) 1 or a dispersive one, for instance on ODE (Baudelet et al, 2011(Baudelet et al, , 2016 at SOLEIL (France), ID24 ISSN 1600-5775 (Mathon et al, 2004;Pascarelli et al, 2016) at ESRF, EDXAS (Cezar et al, 2010) at LNLS (Brazil), or BL-08 (Patra et al, 2019) at Indus-2 (India).…”

Crystal Structure and Chemical Characterization of La0.7Sr0.3Mn0.7Ti0.3-xAlxO3 (0 ≤ x ≤ 0.15) Compounds

“…This model suggests real electron transfer from Mn 3+ (Co 3+ ) to Mn 4+ (Co 4+ ) while this mechanism is effective only for the mixedvalence systems. However, it was found that the ferromagnetic state can be stabilized in some compounds where manganese or cobalt ions are in 3+ or 4+ oxidation state only [3][4][5][6][7][8][9][10][11]. Orbitally disordered state in parent LaMnO 3 above 750 K results in dominant ferromagnetic interactions, as confirmed by the positive Weiss constant (θ ≈ 160 K [3,4]).…”

“…Orbital ordering leads to anisotropic superexchange interactions and Atype antiferromagnetic order below 140 K [3]. The longrange ferromagnetic component has been observed in the LaMn 1−x Ga x O 3 (0.2 < x < 0.6) and LaMn 1−x Cr x O 3 (0.4 < x < 0.6) series containing only Mn 3+ species [5][6][7][8][9][10][11]. These series show gradual transition into the orbitally disordered state upon substitution with Ga 3+ (x > 0.…”