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Register a new userMuon spin rotation and neutron scattering investigations of the B-site ordered double perovskite Sr2DyRuO6
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The magnetic ground state of double perovskite Sr2DyRuO6 has been investigated using muon spin rotation and relaxation (muSR), neutron powder diffraction (NPD) and inelastic neutron scattering (INS), in addition to heat capacity and magnetic susceptibility (ac and dc) measurements. A clear signature of a long-range ordered magnetic ground state has been observed in the heat capacity data, which exhibit two sharp anomalies at 39.5 and 36 K found as well in the magnetic data. Further confirmation of long-range magnetic ordering comes from a sharp drop in the muon initial asymmetry and a peak in the relaxation rate at 40 K, along with a weak anomaly near 36 K. Based on temperature dependent NPD, the low temperature magnetic structure contains two interpenetrating lattices of Dy and Ru5, forming an antiferromagnetic ground state below 39.5 K with magnetic propagation vector k = (0,0,0). The magnetic moments of Dy and Ru at 3.5 K are pointing along the crystallographic b-axis with values of muDy = 4.92(10) muB and muRu = 1.94(7) muB, respectively. The temperature dependence of the Ru moments follows a mean field type behaviour, while that of the Dy moments exhibits a deviation indicating that the primary magnetic ordering is induced by the order of the 4d electrons of Ru rather than that of its proper 4f Dy electrons. The origin of the second anomaly observed in the heat capacity data at 36.5 K must be connected to a very small spin reorientation as the NPD studies do not reveal any clear change in the observed magnetic Bragg peaks positions or intensities between these two transitions. INS measurements reveal the presence of crystal field excitations (CEF) in the paramagnetic state with overall CEF splitting of 73.8 meV, in agreement with the point change model calculations.
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We have performed dielectric measurements and neutron diffraction experiments on the double perovskite In2NiMnO6. A ferroelectric polarization, P ~ 30 {mu}C/m2, is observed in a polycrystalline sample below TN = 26 K where a magnetic phase ransition occurs. The neutron diffraction experiment demonstrates that a complex noncollinear magnetic structure with cycloidal and proper screw components appears below TN, which has the incommensurate propagation vector k = (ka,0,ks; ka ~ 0.274, ks ~ -0.0893). The established magnetic point group 21 implies that the macroscopic ferroelectric polarization is along the monoclinic b axis. Recent theories based on the inverse Dzyaloshinskii-Moriya effect allow us to specify two distinct contributions to the polarization of In2NiMnO6. One of them is associated with the cycloidal component, p1 ~ rij x (Si x Sj), and the other with the proper screw component, p2 ~ [rij (Si x Sj )]A. The latter is explained by coupling between spin helicity and ferriaxial crystal rotation with macroscopic ferroaxial vector A, characteristic of the B-site ordered perovskite systems with out-of-plane octahedral tilting.
The magnetic and quadrupolar ordered states of polycrystalline YbRu2Ge2 have been investigated using zero-field muon spin relaxation ({mu}SR) and neutron diffraction measurements. Specific heat measurements show three successive phase transitions, with decreasing temperature from a paramagnetic to a quadrupolar state at T0 ~ 10 K, from the quadrupolar to a magnetic state at T1 ~ 6.5 K and a possible change in the magnetic ground state at T2 ~ 5.5 K. Clear evidence for the magnetic transition below 7 K (spectrum at 8 K reveals paramagnetic state) and a likely change in the magnetic structure near 5.8 K is observed in the zero-field {mu}SR measurements. The {mu}SR data, however, do not reveal any signature of magnetic order in the temperature range 8 - 45 K. This result is further supported by neutron diffraction measurements, where clear magnetic Bragg peaks have been observed below 8 K, but not above it. Below 8 K, the magnetic Bragg peaks can be characterized by an incommensurate antiferromagnetic ordering with the propagation vector q = [0.352, 0, 0] and the magnetic moment 2.9(3) {mu}B of Yb along the b-axis. These results are discussed in terms of quadrupolar ordered and magnetically ordered states.
Magnetic structures and the relationship between spin and charge-orbital orderings of an A-site ordered double-perovskite manganite SmBaMn2O6, an anticipated multiferroic material, were investigated by means of neutron diffraction. The spin arrangement in MnO2 planes perpendicular to the c axis is revealed to be the same as that in the A-site disordered half-doped manganites CE-type but the stacking pattern is found to be different displaying a unique twofold period. The temperature dependence of the superlattice magnetic and nuclear reflections clarifies that the antiferromagnetic spin ordering occurs at a temperature slightly lower than the temperature at which a rearrangement of the charge-orbital orderings occurs. The result evidences that the rearrangement leads the spin ordering. The intensities of the magnetic reflections are found to change across Tf = 10 K, suggesting a spin-flop by 90 [deg.] while keeping the Mn spin ordering pattern unchanged.
Bulk studies have revealed a first-order valence phase transition in Ba$_2$PrRu$_{1-x}$Ir$_x$O$_6$ ($0.10 le x le 0.25$), which is absent in the parent compounds with $x = 0$ (Pr$^{3+}$) and $x =1$ (Pr$^{4+}$), which exhibit antiferromagnetic order with transition temperatures $T_{rm N} = 120$ and 72 K, respectively. In the present study, we have used magnetization, heat capacity, neutron diffraction, inelastic neutron scattering and x-ray absorption measurements to investigate the nature of the Pr ion in $x =0.1$. The magnetic susceptibility and heat capacity of $x =0.1$ show a clear sign of the first order valence phase transition below 175 K, where the Pr valence changes from 3+ to 4+. Neutron diffraction analysis reveals that $x =0.1$ crystallizes in a monoclinic structure with space group $P2_1/n$ at 300 K, but below 175 K two phases coexist, the monoclinic having the Pr ion in a 3+ valence state and a cubic one ($Fmoverline{3}m$) having the Pr ion in a 4+ valence state. Clear evidence of an antiferromagnetic ordering of the Pr and Ru moments is found in the monoclinic phase of the $x = 0.1$ compound below 110 K in the neutron diffraction measurements. Meanwhile the cubic phase remains paramagnetic down to 2 K, a temperature below which heat capacity and susceptibility measurements reveal a ferromagnetic ordering. High energy inelastic neutron scattering data reveal well-defined high-energy magnetic excitations near 264 meV at temperatures below the valence transition. The high energy excitations are assigned to the Pr$^{4+}$ ions in the cubic phase and the low energy excitations to the Pr$^{3+}$ ions in the monoclinic phase. Further direct evidence of the Pr valence transition has been obtained from the x-ray absorption spectroscopy.
B-site ordered thin films of double perovskite Sr$_2$CoIrO$_6$ were epitaxially grown by a metal-organic aerosol deposition technique on various substrates, actuating different strain states. X-ray diffraction, transmission electron microscopy and polarized far-field Raman spectroscopy confirm the strained epitaxial growth on all used substrates. Polarization dependent Co $L_{2,3}$ X-ray absorption spectroscopy reveals a change of the magnetic easy axis of the antiferromagnetically ordered (high-spin) Co$^{3+}$ sublattice within the strain series. By reversing the applied strain direction from tensile to compressive, the easy axis changes abruptly from in-plane to out-of-plane orientation. The low-temperature magnetoresistance changes its sign respectively and is described by a combination of weak anti-localization and anisotropic magnetoresistance effects.
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