Magnetic structure and transport properties of noncollinearLaMn2X2(X=Ge,Si)systems (original) (raw)
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Physica B: Condensed Matter, 2004
The intermetallic ternary compounds of the type RMn 2 X 2 (R=Ca, La, Ba, Y and X=Si, Ge), crystallizing in the ThCr 2 Si 2 structure, show a large variety of collinear and noncollinear magnetic ground states (GS) depending on R and X and thus are good candidates for studying the dependence of the band structure contribution to the electronic transport on the different magnetic configurations. In this contribution we focus our analysis on LaMn 2 Ge 2 : A qualitative understanding of the change in the conductivities with the magnetic structure in this material is provided on the basis of its coherent electronic structure.
2022
The structural and magnetic properties of the ThCr2Si2-type solid solution LaMn2(Ge1−xSix)2 (x = 0.0 to 1.0) have been investigated employing a combination of X-ray diffraction, magnetization and neutron diffraction measurements, which allowed establishing a magnetic composition-temperature phase diagram. Substitution of Ge by Si leads to a compression of the unit cell, which affects the magnetic exchange interactions. In particular, the magnetic structure of LaMn2(Ge1−xSix)2 is strongly affected by the unit cell parameter c, related to the separation of adjacent Mn layers. Commensurate antiferromagnetic layers and a canted ferromagnetic structure dominate the Si-rich part of the solid solution, whilst an incommensurate antiferromagnetic flat spiral and a conical magnetic structure are observed in the Si-poor part.
Applied Physics Letters, 2007
Homogeneous Mn x Ge 1−x ferromagnetic semiconductor films with high Mn concentration were prepared, contrasting with dilute inhomogeneous Mn x Ge 1−x magnetic semiconductors. The saturation magnetization of Mn 0.57 Ge 0.43 films is high, up to 327 emu/ cm 3 ͑1.04 B /Mn͒ at 5 K, and the Curie temperature is about 213 K. The Mn 0.57 Ge 0.43 films show semiconducting resistance, but the magnetoresistance is negligibly small. The anomalous Hall effect was observed below the Curie temperature, which is consistent with the magnetic measurements. The global ferromagnetism was discussed based on s , p-d exchange coupling between the weakly localized s , p hole carriers and the strongly localized d electrons of the Mn atoms.
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 .
Magnetic order inRMn2Ge2(R=Y,Ca)compounds and their solid solutions withLaMn2Ge2
Physical Review B, 2007
We present a systematic study of the stability of the collinear and noncollinear magnetic states of RMn 2 Ge 2 ͑R =Y,Ca͒ compounds as a function of the lattice parameter so as to simulate alloying with La, using densityfunctional theory calculations. The results allow us to discriminate between chemical and structural factors that determine the magnetic properties of these systems. We find that, to a large extent, the magnetic moments are determined by the interatomic Mn-Mn distance, given by the size of the substitutional atom. We also find that the different magnetic structures appearing along the phase diagrams are to be mainly ascribed to the interstitial electronic density related to the divalent or trivalent character of the R atom.
Journal of Solid State Chemistry, 2003
The crystal structure of the binary gallide compound GaMn is reinvestigated using X-ray diffraction. The structure is quite different from that proposed previously. Although GaMn is reported to crystallize with the Al 8 Cr 5 structure type, space group R3m, we found that the centrosymmetric space group R % 3m; with a ¼ 12:605ð2Þ Å and c ¼ 8:0424ð11Þ Å , was more accurate. Moreover, the atomic positions and the atomic displacement parameters, which are missing in the previous study, are now refined. Thereafter, band structure calculations have been performed using the TB-LMTO-ASA method to understand the electronic and magnetic properties of this compound. Analyses from the band structure, the density of states and the magnetic moments obtained using spinpolarized calculations show the stability of two different magnetic models relative to the nonmagnetic one.
Magnetic properties of Gd1−xCexMn2Ge2 compounds
Solid State Communications, 2001
The crystal structure and magnetic properties of polycrystalline Gd 12x Ce x Mn 2 Ge 2 (x 0:0 2 1:0) compounds with the ThCr 2 Si 2 -type structure have been investigated and the magnetic phase diagram has been constructed. The ferromagnetism observed in CeMn 2 Ge 2 transforms to ferrimagnetism with the substitution of Gd for Ce. An additional high temperature ferromagnetic phase in GdMn 2 Ge 2 weakens and eventually disappears with the addition of Ce. The saturation magnetization with increasing x at 4.2 K decreases up to the x 0:5, and then increases again. q