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3413. Comparing magnetism in isostructural oxides A[sub](0.8)La[sub](1.2)MnO[sub](4.1) : anisotropic spin glass (A = Ba) versus long range order (A = Sr)Mirela Dragomir, Paul A. Dube, Iztok Arčon, Chad Boyer, Meghan Rutherford, Christopher Wiebe, Graham King, Hanna Dabkowska, John E. Greedan, 2019, izvirni znanstveni članek Opis: This study presents the strikingly distinct magnetic properties of two isostructural compounds, Ba0.8La1.2MnO4.1
and Sr0.8La1.2MnO4.1 (K2NiF4
type, I4/mmm). Spectroscopic studies have shown that Mn is in a +3.0(1) oxidation state only,
in both compounds; therefore, the charge is balanced by accommodating extra oxygen at interstitial sites, as confirmed by
neutron powder diffraction. We found that the Ba compound exhibits an exceedingly rare anisotropic spin glass behavior, Tg =
26.4(4) K, with the moment freezing along the c-axis only while the in-plane spin components remain dynamic well below Tg.
Experimental results including neutron diffraction, heat capacity, and magnetic (dc and ac) measurements performed on an
oriented single crystal support this conclusion. This is a remarkable result, the only other known example of an anisotropic spin
glass being Fe2TiO5. The spin glass state in Ba0.8La1.2MnO4.1 is argued to arise due to competing antiferromagnetic and
ferromagnetic 180° Mn3+−O−Mn3+ superexchange interactions. In contrast, the Sr analogue shows 2D antiferromagnetic
correlations and long-range antiferromagnetic order below 95(1) K with a remarkably reduced ordered moment of 1.449(49)
μB/Mn3+ instead of the ∼4 μB expected for an S = 2 ion. Ključne besede: antiferomagnetiki, Mn XANES, struktura Objavljeno v RUNG: 23.10.2019; Ogledov: 3159; Prenosov: 0 Gradivo ima več datotek! Več... |
3414. In-depth structural characterization and magnetic properties ofquaternary ferrite systems Co0.5Zn0.25M0.25Fe2O4(M¼Ni, Cu, Mn, Mg)Radu-G. Ciocarlan, Iztok Arčon, Aurel Pui, Myrjam Mertens, Nataša Novak Tušar, Elena M. Seftel, Pegie Cool, 2019, izvirni znanstveni članek Opis: This paper investigates the structural and magnetic properties of a mixed series of ferrites having generalformula Co0.5Zn0.25M0.25Fe2O4(M¼Ni, Cu, Mn, Mg). Insights on surface chemistry, structural andmorphological parameters are presented in order to achieve highly tuned ferrite systems with specificcharacteristics. The site occupancy of the cations in the spinel structure was determined using XAS, XRDand Raman spectroscopy. A 100% occupancy of the tetrahedral sites was observed for the Zn cations forall the samples. Co cations occupied the octahedral sites in proportion of 100% for CoeZneCu, CoeZneMg and around 80% for CoeZneNi, CoeZneMn. Ni cations were found only in the octahedral sites,while Cu 80% in the octahedral sites and Mn 60% in the octahedral sites. The cation distribution resultswere correlated with the magnetic properties data. At the same time, not only the cation distribution, butalso the particles size distribution was observed to have a great influence on magnetic and opticalproperties of the ferrites. Given the importance of the surface chemistry of the nanoparticles, XPS and FT-IR analysis were used to prove the functionalization with groups belonging to the surfactant. Moreover,the peculiar behavior of manganese in spinel structures was clarified and the origin of the multiple states(Mn2þand Mn4þ) was elucidated. Finally, parallels have been drawn between the use of different cationsin mixed ferrites in order to gain specific properties. Ključne besede: FerritesMagnetic propertiesSpinel nanoparticlesX-ray absorption spectroscopyCo-precipitation Objavljeno v RUNG: 23.10.2019; Ogledov: 3289; Prenosov: 0 Gradivo ima več datotek! Več... |
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