Magnetic properties of rare-earth-doped La_0.7Sr_0.3MnO₃

Abstract

Rare-earth-doped ferromagnetic manganites LaRESrMnO (RE = Gd, Tb, Dy, and Ho) are synthesized in the form of sintered ceramics and nanocrystalline phases with the mean size of crystallites ≈30 nm. The electronic states of the dopants are investigated by SQUID magnetometry and theoretically interpreted based on the calculations of the crystal field splitting of rare-earth energy levels. The samples show the orthorhombic perovskite structure of Ibmm symmetry, with a complete FM order of Mn spins in bulk and reduced order in nanoparticles. Non-zero moments are also detected at the perovskite A sites, which can be attributed to magnetic polarization of the rare-earth dopants. The measurements in external field up to 70 kOe show a standard Curie-type contribution of the spin-only moments of Gd ions, whereas Kramers ions Dy and non-Kramers ions Ho contribute by Ising moments due to their doublet ground states. The behaviour of non-Kramers ions Tb is anomalous, pointing to singlet ground state with giant Van Vleck paramagnetism. The Tb doping leads also to a notably increased coercivity compared to other LaRESrMnO systems.

Easy Synthesis and Characterization of Holmium-Doped SPIONs

“…The observed degradation of magnetic properties of studied ferrites is consistent with a two-phase approach of the so-called core-shell model, which is commonly used in analysis of fine structured materials [ 54 ]. The magnetic and electrical properties of transition-metal-based oxides are known to be strongly affected by various types of structural and chemical disorder [ 54 , 58 , 59 , 60 ]. The level of disorder may be accounted for by the volume fraction of disordered phase contained in the solid.…”

Effect of Tb3+doping in mixed-valence manganites and cobaltites

“…Similarly large Tb 3+ moments have been detected for the Tb-doped cobaltite La 1−x Ca x CoO 3 having a similar strongly distorted orthoperovskite structure [17]. On the contrary, there are very recent reports on the Tb 3+ doping in La 1−x Sr x MnO 3 manganites of the rhombohedral R3c perovskite structure, which point to a significant splitting of Tb 3+ quasi-doublet, being of 1 meV order [18,19]. In such a case, the Tb 3+ ions contribute at the lowest temperatures by giant Van Vleck paramagnetism-they carry no magnetic moment (no first order Zeeman splitting) unless local magnetic fields of external or molecular origin are present.…”

“…for La 0.7 Tb 0.1 Sr 0.2 MnO 3 at 2 K, is apparently spread over large temperature range instead of forming a common Curie tail. Such behaviour is a signature for existence of giant Van Vleck paramagnetism due to Tb 3+ ions in singlet ground state [18,19]. The data for cobaltite systems in right panel of figure 4 illustrate a completely different behaviour.…”

Oxygen nonstoichiometry and magnetic properties of doped manganites La0.7Sr0.3Mn0.95Fe0.05O3-δ

“…It is known that in La 0.7 Sr 0.3 MnO 3-δ -manganites the value of δ cannot be higher than 3, since at δ > 3 the perovskite structure is unstable and attempts to obtain compositions with δ > 3 lead to the appearance of vacancies in the manganese and rare-earth sublattices [16][17][18][19][20][21][22][23][24][25][26]. In this case, the physico-chemical properties of manganite with the composition La 0.6 Sr 0.4 MnO 3-δ largely depend on the oxygen nonstoichiometry, which affects the oxidation state of manganese (Mn 4+ and Mn 3+ with electronic configurations t 3 2g e g 1 (S = 2) and t 3 2g e g 0 (S = 3/2), respectively) and electronic exchange between Mn 3+ and Mn 4+ [16][17][18][19][20][21][22][23][24][25][26]. Crystal lattice distortions caused by defectiveness in the anion sublattice affect the bonds and the spatial arrangement of the Mn 4+ -O-Mn 3+ chains, changing the magnitude of exchange interactions that depend both on the overlap of electron orbitals and on the bond angle between them.…”

“…where the spins of S n and S n+p cations n and n + p are located at the nearest neighboring nodes. In this case, the value of the constant J n,n+p is determined by the superexchange interaction through the p σ and p π states of the О 2anions [16][17][18][19][20][21][22][23][24][25][26].…”