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MAGNETIC SYSTEMS 2009Nd 3+ crystal-field studies of weakly doped Nd 1−x Ca x MnO 3Manganites RMnO 3 compounds based on lanthanides (R)are antiferromagnetic systems with important Jahn-Tellerdistortions. Substitution of lanthanides by Ba, Sr, or Caleads to appearance of double exchange interactions, reductionof Jahn-Teller-type distortions and simultaneous observationof metallic and ferromagnetic character with increasingmolar fraction x (R 1−x A x MnO 3 , A = Ba, Sr, orCa). In this work, Nd 3+ ions crystal field (CF) excitationsin Nd 1−x Ca x MnO 3 (x = 0.025, 0.05 and 0.1) singlecrystals have been investigated using infrared transmissionspectroscopy at different temperatures and external magneticfields and compared to undoped NdMnO 3 .Our study reveals the presence of a magnetic phase separationin the doped samples. As a consequence of dopingby calcium, we report the detection of two sets ofCF levels, as already observed in Nd 1−x Sr x MnO 3 [see S.Jandl et al., Phys. Rev. B 71, 024417 (2005) and S.Jandl et al., ibid 72, 024423 (2005)]. One is associatedwith unperturbed sites related to the NdMnO 3 antiferromagnetismwith its typical Zeeman splitting below Neeltemperature, and a second one is linked to perturbed sitesin the vicinity of the Ca 2+ cations where local A-typeantiferromagnetism is suppressed. While the energy differencesbetween the two sets are within the uncertaintyvalues of the CF parameters that describe the NdMnO 3CF Hamiltonian and predict the CF levels, their detectionstrengthens the role of local probe the rare-earth CF levelsplay in manganite compounds. Finally, under appliedexternal magnetic field, Zeeman splittings are observed inNdMnO 3 and Nd 0.975 Ca 0.025 MnO 3 , while they are maskedin Nd 0.95 Ca 0.05 MnO 3 and Nd 0.9 Ca 0.1 MnO 3 . The latter resultsare due to doping-induced band broadening and possibletwining.The Zeeman splitting well-resolved at lower doping densitiesis demonstrated in Fig. 104, where the middle-infraredtransmission spectra of investigated samples taken withoutand with the externally applied magnetic field (parts A andB) are presented. For details see, S. Jandl et al., J. Magn.Magn. Mater. 321, 3607 (2009).Figure 104: Transmission spectra showing 4 I 9/2 → 4 I 11/2 Nd 3+transitions in Nd 1−x Ca x MnO 3 at T = 1.8 K: x = 0 (a), x = 0.025(b), x = 0.05 (c) and x = 0.1 (d) measured at (A) B = 0 T andB = 12 T. ∗ indicates the new CF excitations that are due to thedoping. The Zeemen splitting is well-resolved at lower concentrations(x = 0 and 0.025) but masked at higher doping densities.M. OrlitaS. Jandl (University of Sherbrooke, Canada), A. A. Mukhin, V. Yu. Ivanov (General Physics Institute of the RussianAcademy of Sciences, Moscow, Russia), A. Balbashov (Moscow Power Engineering Institute, Moscow, Russia)78