Abstract
A high-pressure synthesis method was employed to prepare Mn-self-doped perovskites (R 0.667Mn0.333)MnO3 (R = Yb, Lu) at about 6 GPa and 1670 K. Crystal and magnetic structures of (Yb0.667Mn0.333)MnO3 have been studied by combining neutron powder diffraction, magnetic susceptibility and specific heat measurements. Within the orthorhombic space group Pnma, magnetic cations are located on site 4c (A site, occupied by two thirds of Yb3+ and one third of Mn2+) and on site 4b (B site, occupied by two thirds of Mn3+ and one third of Mn4+). The degree of structural distortion of the MnO6 octahedra follows the general trend of (R1−x Mn x )MnO3 compounds which shows a decrease with increasing amount of Jahn–Teller inactive Mn4+ cations. Mn–Mn interactions produce a collinear ferrimagnetic structure (T C,Mn = 106 K) with ferromagnetically ordered Mn moments at the B site being coupled antiferromagnetically with ordered Mn moments at the A site. Mn–Yb interactions induce a small but non-zero ferromagnetic Yb3+ moment which can explain a small decrease of the magnetic susceptibility at low temperature. Yb–Yb interactions create an antiferromagnetic structure at T N,Yb ≈ 40 K. Ordered moments of the ferrimagnetic and antiferromagnetic structures are oriented perpendicular to each other within the ac-plane and Yb3+ moments contribute to both structures. The appearance of ordered Yb3+ moments induced by Mn–Yb interactions in perovskite (Yb0.667Mn0.333)MnO3 is a result of the Mn self-doping on the A site and has not been observed in the orthorhombic perovskite modification (space group Pnma) of the undoped parent compound YbMnO3, but interestingly, it also appears in the hexagonal non-perovskite modification (space group P63 cm) of YbMnO3.
Highlights
Perovskite-structure manganites, RMnO3 with R = rare earth cations or Y, exhibit many technically important unusual structural and physical properties
They all have the same crystal structure—the so-called GdFeO3-type distortion of perovskites with space group Pnma and the a+b−b− Glazer tilt system. They all have the same orbital ordering pattern but with large variations of the orbital-ordering temperature from about 870 K for LaMnO3 to about 1500 K for DyMnO3 [1]. Their magnetic ground states and magnetic phase transition sequences strongly depend on structural distortions [2] or magnitudes of octahedral tilts
In EuMnO3 and GdMnO3, the first magnetic transition is to an incommensurate (IC) AFM phase, which changes to the A-type AFM phase [4, 5]
Summary
Apart from the difference of the magnetic form factors for Yb3+ and Mn2+ (not accurate), our NPD data cannot unambiguously distinguish between the contributions from the two thirds of Yb3+ and one third of Mn2+ cations to the average ordered moment at the A site (−f x,ave, cz,ave) and we had to use an approximation by taking into account results of specific heat measurements for (Yb0.667Mn0.333)MnO3 and (Lu0.667Mn0.333)MnO3, as well as of previous NPD experiments on (Lu0.6Mn0.3)MnO3) [18].
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