Magnetism in NdMn0.1Fe0.9O3 compound

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Highlights

  • Neutron powder diffraction experiments in temperature range 20 mK–300 K.

  • Completing the magnetic phase diagram of NdMn1−xFexO3 substitutional system.

  • X-rays and neutrons used as complementary probe.

Abstract

The low temperature crystal and magnetic structures of NdMn0.1Fe0.9O3 were determined on the basis of X-ray and neutron powder diffraction experiments as well as from specific heat and magnetization measurements. The compound crystallizes in the orthorhombic crystal structure, space group Pnma, in the entire temperature interval 20 mK < T < 300 K. The lattice parameters exhibit standard thermal expansion effects for T > 20 K and at lower temperatures the anomalies due to magnetostriction effect were observed. The iron sublattice orders magnetically into 3 different magnetic structures, namely into Γ5 = (Ax, Fy, Gz) for 130 K < T < TN (Néel temperature); Γ1 = (Gx, Cy, Az) for 15 K < T < 130 K and Γ3 = (Cx, Gy, Fz) for 20 mK < T < 15 K. The Nd ions order at temperatures below 1.6–1.75 K into the same Γ3 phase as the iron sublattice at these temperatures. The obtained magnetic structures fit perfectly in between the magnetic phases of closely related NdFeO3 and NdMn0.5Fe0.5O3 compounds. Our study, together with all previously published data, completes the entire magnetic phase diagram of NdMn1−xFexO3 (0 ≤ x ≤ 1) solid solution substitutional system.

Introduction

Distorted perovskite structure oxides, of which manganites (general formula: REMnO3; RE = Rare earth) and orthoferrites (general formula REFeO3) are a subset, host multiferroicity, magnetoelectricity, complex magnetic structures and other interesting physical phenomena. For example, La1−xCaxMnO3 and La1−xSrxMnO3 exhibit colossal magnetoresistance [1] and TbMnO3 compound exhibits multiferroic behavior [2].

The magnetic structure of these compounds is driven by the competition between the double exchange, superexchange, and Dzyaloshinskii-Moriya interactions [3]. These interactions strongly depend on the structural changes induced by doping. For that reason the magnetism in these systems is affected by doping, too. Various substitutions are frequently used to probe the magnetic interaction in these materials either in the RE site [1], [4], [5], or in the transition metal site [6], [7], [8], [9], [10], [11]. The transition metal site substitution, especially Mn-Fe substitution looks interesting, since Mn3+ is Jahn-Teller (JT) active ion, while Fe3+ is not. Both ions have in the high spin state and coordination number 6 (our case) the same effective Shanon radii [12], so the structural change induced by the Mn-Fe substitution is directly connected with the lifting of the JT distortion in the system.

NdMn1−xFexO3 system is a magnetic insulator that crystallizes in the orthorhombic crystal structure (space group Pnma1) and contains three magnetic ions with well-documented magnetochemistry [13]. The Nd3+ has a 4f3, 10-fold degenerate magnetic 4I ground state that is split and mixed in the perovskite host lattice to have both orbital and spin components. The Mn3+ ion is S = 2, 3d4 with a Jahn-Teller active 5Eg ground state and the Fe3+ ion has a half-filled d-shell S = 5/2, 6A1 ground state.

The first neutron diffraction study of NdFeO3 compound reported that the compound orders antiferromagnetically with TN = 760 K [14]. Several, more detailed later neutron diffraction studies [15], [16] settled up that in NdFeO3 the Fe sublattice orders at TN into (0, Fy, Gz) structure with weak ferromagnetic component and undergoes spin reorientation phase transition at temperatures 100 K < T < 200 K into the low temperature (0, Gy, Fz) structure [15]. Bartolome et al. [16] reported that Nd3+ ions polarize already at 25 K due to Nd-Fe interaction, but the true ordering due to Nd-Nd magnetic interaction takes place only below 1.05(1) K [17]. The different situation is in the NdMnO3 compound. In this compound the Mn3+ ions order antiferromagnetically at TN = 82 K into (Ax, Fy, 0) [18] or (Ax, 0, 0) magnetic structure with subsequent transition into (Ax, Fy, 0) state at lower temperatures [19]. The Nd ions order below T1 = 20 K into (0, fy, 0) magnetic structure [18], [19]. It is noteworthy that Nd ions are polarized already at 55 K > T > T1 [20].

The iron substitution of manganese in the NdMnO3 compound generates Gz component for Mn sublattice for NdMn0.8Fe0.2O3 compound [21] and the extension of the temperature interval in which the Nd ions are ordered [21]. Further doping leads to suppression of the magnetism in NdMn0.7Fe0.3O3 compound [22]. For 50% of iron doping (compound NdMn0.5Fe0.5O3), the situation changes, and the magnetism is most probably already driven by iron ions. For this composition, the Gx magnetic configuration of manganese and iron ions was reported in temperature range 75 K < T < TN (=250 K) [23]. In temperature range 25 < T < 75 K this system undergoes spin reorientation phase transition into Gy low temperature magnetic structure, where the noticeable Fz component is observed at 1.5 K due to Nd ions [23]. The reported magnetic structures for NdMn0.5Fe0.5O3 are different from the presented magnetic scenario of NdFeO3, so the magnetism in this system should somehow evolve even in this concentration range. Since there is only scarce information about the Fe-rich part of this substitutional system, we decided to study the magnetism of NdMn0.1Fe0.9O3 compound in detail. Herein, we present our results and we propose the magnetic phase diagram of NdMn0.1Fe0.9O3 compound for temperatures 20 mK < T < TN (≈650 K).

Section snippets

Sample preparation experimental setup and analysis protocols

Samples were prepared by a vertical floating zone (FZ) method in an optical mirror furnace. The starting materials consisted of high-purity oxides of MnO2 (purity: 99.9%, producer: Alpha Aesar), Nd2O3 (purity 99.9%, producer: Sigma Aldrich), and Fe2O3 (purity 99%, producer: Sigma Aldrich). The starting materials were mixed in a stoichiometric ratio, isostatically cold-pressed into rods, and subsequently sintered at 1373 K for 12 h in air. The floating zone experiment was performed using a

Crystal structure refinement

Since all reported members from the NdMn1−xFexO3 family [15], [18], [22], [23], [25], [29] crystallize in the orthorhombic crystal structure, space group Pnma (#62 according to the International Tables for Crystallography [30]), we have used the same crystallographic model also for NdMn0.1Fe0.9O3 compound. In this model, the Nd ions occupy 4c (xNd ≈ 0.05; zNd ≈ 0.98) crystallographic position, Fe and Mn ions are randomly distributed on 4b crystallographic site and oxygen ions occupy two

Discussion

Our study revealed four magnetic phase transitions at different temperatures: TN ≈ 748 K [26] (paramagnetic to magnetic ordering phase transition); T1 = 130 K; T2 = 15 K and T3 ≈ 1.6 K (Fig. 7). The magnetic structure in the range TN > T > T1 is of the Γ5 type. In this interval the strongest magnetic component is along the c-axis and is antiferromagnetically coupled (Fig. 7). The ferromagnetic component aligns along the b-axis and is much weaker than the c-axis component. The component along

Conclusions

Our low temperature X-ray and neutron powder diffraction study confirmed that NdMn0.1Fe0.9O3 adopts orthorhombic crystal structure Pnma and did not reveal any transition of crystal structure in the entire temperature range 20 mK < T < 300 K. The lattice parameters exhibit standard thermal expansion effects for T > 20 K but below this temperature the anomalies due to magnetostriction effects were observed. Results of NPD measurements are in agreement with magnetic structure proposed from

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We thankfully acknowledge the financial support by HZB. The research was also supported by VEGA project No. 2/0137/19, ERDF EU under Contract No. ITMS-26220220061 and Grant Agency of the Czech Republic, project 19-00408S.

References (32)

  • V.L. Mathe et al.

    J. Magn. Magn. Mater.

    (2004)
  • M. Mihalik et al.

    Phys. B

    (2017)
  • F. Bartolomé et al.

    Solid State Sci.

    (2005)
  • A. Tiwari

    J. Alloys Compd.

    (1998)
  • M. Mihalik et al.

    J. Alloys Compd.

    (2016)
  • R. Vilarinho et al.

    J. Magn. Magn. Mater.

    (2017)
  • F. Bartolomé et al.

    Solid State Commun.

    (1994)
  • M. Mihalik et al.

    J. Magn. Magn. Mater.

    (2013)
  • Marián Mihalik et al.

    Phys. B

    (2018)
  • J. Rodríguez-Carvajal

    Phys. B

    (1993)
  • W. Sławiński et al.

    Nucl. Instrum. Methods Phys. Res. B

    (2007)
  • R. Przeniosło et al.

    J. Magn. Magn. Mater.

    (1995)
  • A.P. Ramirez

    J. Phys.: Condens. Matter

    (1997)
  • T. Kimura et al.

    Nature

    (2003)
  • I.A. Sergienko et al.

    Phys. Rev. B

    (2006)
  • M. Antoňák et al.

    Acta Phys. Pol. A

    (2014)
  • Cited by (0)

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