Spin reversal, magnetic domains and relaxation mechanisms in Er(Co,Mn)O3 perovskites
Introduction
The discovery of giant magneto-resistance in manganese oxides has resulted in a renewed interest in mixed-valence manganese perovskites over the last decades because of the many possible technological applications and the very interesting physics coming from the inter-relation between structural, magnetic and transport properties [1], [2], [3]. The key feature is the double-exchange mechanism due to the simultaneous presence of Mn3+ and Mn4+ ions, which triggers the well-known insulating-conducting phase transitions [4], [5], [6], [7]. Most of the reports describe the physico-chemical properties of doped ABO3 perovskites, where the A-site, occupied by a rare-earth element RE, is partially substituted by an alkaline-earth. Substitutions of the manganese ion situated at the B-site are less frequently studied, in spite of the fact that similar transformations Mn3+ → Mn4+ trigger also the ferromagnetic exchange interactions. In this latter case, the general formulation would be RE3+Me2+xMn3+1 − 2xMn4+xO2−3 (where Me stands for a transition-metal element).
The presence of two magnetic networks composed of the transition metal and the lanthanide elements will lead to important cooperative effects. Interesting features may then occur if the rare-earth element bears a strong magnetic moment since it may interact with the manganese spins through the internal field imposed by the ferromagnetically ordered Mn sublattice [8]. As such, spectacular behaviours have been observed by us in the case of RE = Er, for which several anomalies were reported : a spin reversal, a field-induced transition and an intersection of the increasing and decreasing branches of the magnetization loops M(H) [9], [10].
We report herein the magnetic properties of the Er(Co,Mn)O3 solid solution, in which several magnetic entities (Mn3+, Mn4+, Co2+, and Co3+) coexist with the Er3+ magnetic moment. We will emphasize the results obtained in three specific cases (x = 0.40, 0.50, and 0.60) of the ErCoxMn1 − xO3 system that are at (or close to) the “magic” substitution rate Mn/Co = 50:50 (ErCo0.50Mn0.50O3) where the ferromagnetic Co2+–Mn4+ interactions are maximized. In order to get a deeper insight on these phenomena, we have performed magnetization cycles as a function of temperature (iso-field ZFC/FC) and field (isothermal M–vs–H loops), together with high magnetic field studies (up to 23 T). In addition, magnetic relaxation performed at fixed temperature and field allowed us to get a good knowledge of the dynamical character of the magnetic transition.
Section snippets
Experimental
The solid solutions were prepared by classical solid state methods, using submicronic powder oxides RE2O3, MnO and Co3O4. The mixtures were mixed and homogenized by attrition milling using isopropanol as liquid medium, calcined and re-milled three times to assure a total reaction. Synthesis was performed in air at a heating rate of 5 °C/min until the reaction temperature was reached and held at 1150 ºC for 6 h, then cooled at 1 °C/min. Sintering was performed under oxygen flow at 1250 °C for 2 h, and
Results and discussion
Prior to high magnetic field experiments, samples with 0.4 ≤ x(Co) ≤ 0.6 were characterized by ZFC/FC magnetization cycles. The zero-field-cooled (ZFC) process, performed after cooling the sample in the absence of any applied external field and then warming the sample under an applied field of 5 × 10− 3 T (open symbols, Fig. 1), is described by the usual antiferromagnetic spin-canted mechanism for the transition-metal sublattice, that is, antiferromagnetic inter-plane interactions with ferromagnetic
Conclusions
We have shown original magnetic properties of the ErCoxMn1 –-xO3 (x = 0.40, 0.50 and 0.60) orthorhombic perovskites. The iso-field magnetization was interpreted by the existence of two interacting sublattices (one of Er and another of the transition metals Co–Mn), coupled by an antiferromagnetic exchange interaction. The magnetization loop shows a step-like transition at H = 3.5 T for x = 0.50 at T = 2 K. At 4 K, a magnetic field as high as 23 T was unable to saturate the samples' magnetization and no
Acknowledgments
Authors thank the exchange program CNRS-CSIC 18873. High-field measurements performed at the Laboratoire National des Champs Magnétiques Intenses, CNRS, Grenoble, France.
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Magnetic features in REMeO<inf>3</inf> perovskites and their solid solutions (RE=rare-earth, Me=Mn, Cr)
2013, Journal of Magnetism and Magnetic MaterialsCitation Excerpt :The reason for this state of knowledge in exchange anisotropy is that the essential behavior depends critically on the nuclear and spin structures at the atomic level of a buried interface, and the experimental tools to access to this type of information, e.g., atomic-level nuclear and spin-selective photo-emission, Mossbauer spectroscopy, neutron diffraction, chemically resolved TEM imaging, must be applied to this problem. A large amount of work has been lately dedicated to the study of the exchange bias mechanism in coupled thin films of FM and AFM class (see some examples [110b–114]) searching a more complete knowledge of mechanisms that can explain the EB behavior (Fig. 26). Dong et al. [116] proposed that both the Dzyaloshinsky–Moriya interaction and the standard superexchange (the latter, active only when multiferroic materials which can be controlled by electric fields are involved) could induce the exchange bias phenomenon at the FM/G-AFM perovskite oxides interfaces, (in G-type AFM materials, all nearest neighbor spins are antiparallel; Fig. 27 [115]) even when the antiferromagnetic spins are compensated.
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Present address: Instituto de Ciencias de Materiales de Aragon, CSIC, Universidad de Zaragoza, 50009 Zaragoza, Spain.