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Register a new userMagnetic structures and magnetoelastic coupling of Fe-doped hexagonal manganites LuMn1-xFexO3 (0 < x < 0.3)
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We have studied the crystal and magnetic structures of Fe-doped hexagonal manganites LuMn1-xFexO3 (x = 0, 0.1, 0.2, and 0.3) by using bulk magnetization and neutron powder diffraction methods. The samples crystalize consistently in a hexagonal structure and maintain the space group P63cm from 2 to 300 K. The Neel temperature TN increases continuously with increasing Fe-doping. In contrast to a single {Gamma}4 representation in LuMnO3, the magnetic ground state of the Fe-doped samples can only be described with a spin configuration described by a mixture of {Gamma}3 (P63cm) and {Gamma}4 (P63cm) representations, whose contributions have been quantitatively estimated. The drastic effect of Fe-doping is highlighted by composition-dependent spin reorientations. A phase diagram of the entire composition series is proposed based on the present results and those reported in literature. Our result demonstrates the importance of tailoring compositions in increasing magnetic transition temperatures of multiferroic systems.
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Strong spin-lattice coupling and prominent frustration effects observed in the 50$%$ Fe-doped frustrated hexagonal ($h$)LuMnO$_3$ are reported. A N{e}el transition at $T_{mathrm N} approx$ 112~K and a possible spin re-orientation transition at $T_{mathrm {SR}} approx$ 55~K are observed in the magnetization data. From neutron powder diffraction data, the nuclear structure at and below 300~K was refined in polar $P6_3cm$ space group. While the magnetic structure of LuMnO$_3$ belongs to the $Gamma_4$ ($P6_3cm$) representation, that of LuFe$_{0.5}$Mn$_{0.5}$O$_3$ belongs to $Gamma_1$ ($P6_3cm$) which is supported by the strong intensity for the $mathbf{(100)}$ reflection and also judging by the presence of spin-lattice coupling. The refined atomic positions for Lu and Mn/Fe indicate significant atomic displacements at $T_{mathrm N}$ and $T_{mathrm {SR}}$ which confirms strong spin-lattice coupling. Our results complement the discovery of room temperature multiferroicity in thin films of $h$LuFeO$_3$ and would give impetus to study LuFe$_{1-x}$Mn$_x$O$_3$ systems as potential multiferroics where electric polarization is linked to giant atomic displacements.
Here we report the structural, electrical and magnetic properties of Fe doped La0.7Ca0.3Mn1-xFexO3 with x = 0.0 to 1.0 prepared by conventional solid state reaction method. Simulated data on XRD shows an increase in volume with an increase in Fe ion concentration. XPS supports that Fe3+ ions directly substitute Mn3+ ions. Shifting towards lower wave-number and symmetric IR band structure confirms increase in volume and homogeneous distribution of Fe ions. Fe ion doesnt contribute in double-exchange (DE) conduction mechanism due to its stable half filled 3d orbital. The presence of Fe3+ ions encourages anti-ferromagnetism (AFM) generated by super-exchange interaction and suppress insulator-metal transition temperature (TIM). Magnetic measurements show the existence of magnetic polarons supported by increase in volume of unit cell and deviation from Curie-Weiss law.
We employ time-resolved resonant x-ray diffraction to study the melting of charge order and the associated insulator-metal transition in the doped manganite Pr$_{0.5}$Ca$_{0.5}$MnO$_3$ after resonant excitation of a high-frequency infrared-active lattice mode. We find that the charge order reduces promptly and highly nonlinearly as function of excitation fluence. Density functional theory calculations suggest that direct anharmonic coupling between the excited lattice mode and the electronic structure drive these dynamics, highlighting a new avenue of nonlinear phonon control.
The series of intermetallic compounds $R$NiSi$_3$ ($R$ = rare earth) shows interesting magnetic properties evolving with $R$ and metamagnetic transitions under applied magnetic field for some of the compounds. The microscopic magnetic structures must be determined to rationalize such rich behavior. Here, resonant x-ray magnetic diffraction experiments are performed on single crystals of GdNiSi$_{3}$ and TbNiSi$_{3}$ at zero field. The primitive magnetic unit cell matches the chemical cell below the Neel temperatures $T_{N}$ = 22.2 and 33.2 K, respectively. The magnetic structure is determined to be the same for both compounds (magnetic space group $Cmmm$). It features ferromagnetic {it ac} planes that are stacked in an antiferromagnetic $+-+-$ pattern, with the rare-earth magnetic moments pointing along the $vec{a}$ direction, which contrasts with the $+--+$ stacking and moment direction along the $vec{b}$ axis previously reported for YbNiSi$_3$. This indicates a sign reversal of the coupling constant between second-neighbor $R$ planes as $R$ is varied from Gd and Tb to Yb. The long {it b} lattice parameter of GdNiSi$_{3}$ and TbNiSi$_{3}$ shows a magnetoelastic expansion upon cooling below $T_N$, pointing to the conclusion that the $+-+-$ stacking is stabilized under lattice expansion. A competition between distinct magnetic stacking patterns with similar exchange energies tuned by the size of $R$ sets the stage for the magnetic ground state instability observed along this series.
The short range ordered magnetic correlations have been studied in half doped La0.5Ca0.5-xSrxMnO3 (x = 0.1, 0.3 and 0.4) compounds by polarized neutron scattering technique. On doping Sr2+ for Ca2+ ion, these compounds with x = 0.1, 0.3, and 0.4 exhibit CE-type, mixture of CE-type and A-type, and A-type antiferromagnetic ordering, respectively. Magnetic diffuse scattering is observed in all the compounds above and below their respective magnetic ordering temperatures and is attributed to magnetic polarons. The correlations are primarily ferromagnetic in nature above T_N, although a small antiferromagnetic contribution is also evident. Additionally, in samples x = 0.1 and 0.3 with CE-type antiferromagnetic ordering, superlattice diffuse reflections are observed indicating correlations between magnetic polarons. On lowering temperature below T_N the diffuse scattering corresponding to ferromagnetic correlations is suppressed and the long range ordered antiferromagnetic state is established. However, the short range ordered correlations indicated by enhanced spin flip scattering at low Q coexist with long range ordered state down to 3K. In x = 0.4 sample with A-type antiferromagnetic ordering, superlattice diffuse reflections are absent. Additionally, in comparison to x = 0.1 and 0.3 sample, the enhanced spin flip scattering at low Q is reduced at 310K, and as temperature is reduced below 200K, it becomes negligibly low. The variation of radial correlation function, g(r) with temperature indicates rapid suppression of ferromagnetic correlations at the first nearest neighbor on approaching TN. Sample x = 0.4 exhibits growth of ferromagnetic phase at intermediate temperatures (~ 200K). This has been further explored using SANS and neutron depolarization techniques.
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