Magnetic phase diagram of the solid solution LaMn2(Ge1−xSix)2 (0 ≤ x ≤ 1) unraveled by powder neutron diffraction (original) (raw)
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The LaMn 1Ϫx Ga x O 3 series (xϭ0. 05, 0.1, 0.15, 0.3, 0.4, 0.5, 0.6, 0.8, 0.9) was studied by means of ac magnetic susceptibility, magnetization, and neutron diffraction as a function of temperature. The crystal and magnetic structures have been refined from the neutron diffraction data. The replacement of Mn by Ga induces a continuous decrease of the tetragonal distortion of the MO 6 (MϭMn,Ga) octahedron, being practically regular for xу0.6. Simultaneously, the Ga substitution induces a ferromagnetic component explained in terms of a canting of the A-type antiferromagnetic structure. The ferromagnetic component increases with increasing the Ga content up to xϭ0.5, where a collinear ferromagnetism is observed. For xу0.6, the system evolves from collinear ferromagnetism into superparamagnetism. The occurrence of superparamagnetism for heavily doped samples (xϭ0.8 or 0.9͒ suggests that Mn atoms tend to form clusters.
Structural and magnetic behavior of LaMnO3+δ and LaMn0.9Cr0.1O3+δ at the same “hole concentration”
Journal of Alloys and Compounds, 2004
We report a comparative magnetic and a neutron powder diffraction (NPD) study of un-doped LaMnO 3+δ (δ = 0.05 and 0.09) and Cr doped LaMn 0.9 Cr 0.1 O 3+δ (δ = 0.00 and 0.04) with the same "hole concentration". Samples with controlled oxygen contents were prepared by annealing at different temperatures and p(O 2) values. The refinement of the neutron powder diffraction data at 2 K shows that the AFM components for the Cr doped samples are higher than those of the un-doped ones for the same "hole concentration". The FC and ZFC dc magnetization measurements versus T under 100 Oe also reveal a strong AFM character for the Cr-doped samples. These results clearly show a different role in the magnetic interactions for samples doped with Cr 3+ and Mn 4+ ions.
Magnetic structure and transport properties of noncollinearLaMn2X2(X=Ge,Si)systems
Physical Review B, 2004
Electronic, magnetic, and transport properties of the noncollinear naturally multilayered compounds LaMn 2 Ge 2 and LaMn 2 Si 2 are addressed by first-principles calculations based on the density-functional theory. At low temperatures, these systems show a magnetic state with the Mn moments ordered in a conical arrangement (spin spiral) with a ferromagnetic coupling along the c axis and an in-plane antiferromagnetic coupling. The magnetic structures are studied by means of the full-potential linearized augmented-plane-wave method within both the generalized-gradient approximation and the local-density approximation. In both compounds, a conical magnetic state is obtained with energies lower than canted and collinear structures. The trends in the experimentally observed magnetic configuration when replacing Ge by Si are discussed. The origin of the experimentally observed inverse giant magnetoresistance in LaMn 2 Ge 2 is traced back to the presence of many noncollinear low-energy magnetic configurations.
Journal of Physics and Chemistry of Solids, 1999
Systematic powder diffraction studies have been carried out to establish the magnetic phase diagram of La2−2xSr1+2xMn2O7 (LSMO327) in a wide hall concentration range (0.30 ≤ x ≤ 0.50), using the HERMES diffractometer. LSMO327 exhibits a planar ferromagnetic structure for 0.32 ≤ x ≤ 0.38 at low temperatures. A finite canting angle between planar magnetic moments on neighboring planes starts appearing around x ∼ 0.40 and reaches 180 • (A-type antiferromagnet) at x = 0.48. At x = 0.30, on the other hand, the magnetic moments are aligned parallel to the c-axis.
Magnetic phase transitions in PrMn2−xCrxGe2
Journal of Magnetism and Magnetic Materials, 2002
The structural and magnetic properties of PrMn 2Àx Cr x Ge 2 (0pxp1.0) were studied by X-ray diffraction and magnetization measurements. The powder samples crystallize in the ThCr 2 Si 2 -type structure, and the lattice constants at room temperature show almost no variation as Cr substitutes Mn. The observed phase transitions are summarized in a proposed magnetic x À T phase diagram and compared with previous Moessbauer spectroscopy and neutron diffraction results for x ¼ 0: r (I. Dincer).
Journal of Physics: Condensed Matter, 2010
The crystal structure, electronic and magnetic properties of LaMn 7 O 12 ((LaMn 3+ 3) A Mn 3+ 4 O 12) are investigated by GGA (LSDA) and GGA + U (LSDA + U) (0.0 U 5.0 eV) methods. Based on two experimentally refined structures (distinguished by the distortion parameter , namely S I (= 8.5 × 10 −5) and S II (= 25.0 × 10 −4)), GGA and GGA + U with U < 3.0 eV calculations indicate that S I with a small distortion is the lowest-energy crystal structure while GGA + U with 3.0 U 5.0 eV calculations show that S II with a larger distortion is the ground-state crystal structure. Within the LSDA method, S II is always the ground-state structure no matter if U is considered or not. There are two independent magnetic sublattices: Mn 3+ within the A site and Mn 3+ within the B site. First, it is predicted that A-site Mn 3+ ions are preferably AFM-coupled in G-type (antiferromagnetically coupled in three directions). Based on this result, four magnetic configurations (FM-A ↑↑ B ↑↑ , AFM1-A ↑↑ B ↓↓ , AFM2-A ↑↓ B ↑↑ and AFM3-A ↑↓ B ↑↓) are designed, and their total energies are calculated. Our results demonstrate that AFM2 and AFM3 are the lowest magnetic state, respectively, for S I and S II. Correspondingly, LaMn 7 O 12 is metallic with no orbital ordering at AFM2 for S I while it is an insulator with orbital ordering at AFM3 for S II. Thus, modulation of the distortion parameter , e.g. by chemical doping, could be employed as a new avenue to induce a magnetic phase transition and the corresponding metal-to-insulator transition in LaMn 7 O 12 .