RESUMO
This study reports the effect of 120 MeV swift Au9+ion irradiation on the structures of monoclinic, tetragonal and cubic ZrO2, probed through x-ray diffraction (XRD) and Raman spectroscopy. Three phases of ZrO2were prepared using the solution combustion method. The tetragonal and cubic phases of ZrO2were stabilized at room temperature by adding 6% and 10% of yttrium ions, respectively. Both the XRD and Raman results confirm the partial phase transition from monoclinic to tetragonal, which was approximately 74%. Tetragonal ZrO2is stable under 120 MeV Au9+ion irradiation. Interestingly, a phase transition from cubic to tetragonal ZrO2was observed under 120 MeV Au9+ion irradiation. The roles of transient temperature, defects and strain in the lattice induced by swift heavy ions are discussed. This study reveals the structural stability of different phases of ZrO2under swift heavy ion irradiation and should be helpful in choosing potential hosts for various applications such as inert fuel matrix inside the core of nuclear reactors, oxygen sensors and accelerators, and radiation shielding.
RESUMO
Cubic spinel CoCr2O4 has recently attained attention due to its multiferroic properties. However, the Co site substitution effect on the structural and magnetic properties has rarely been studied in thin film form. In this work, the structural and magnetic properties of Co1-x Ni x Cr2O4 (x= 0, 0.5) epitaxial thin films deposited on MgAl2O4 (100) and MgO (100) substrates to manipulate the nature of strain in the films using pulsed laser deposition (PLD) technique are presented. The epitaxial nature of the films was manifested through x-ray diffraction (XRD), reciprocal space mapping (RSM) and Rutherford backscattering spectrometry (RBS) measurements. Raman measurements revealed a disappearance of characteristic A 1 g and F 2 g modes of the CoCr2O4 with increase in the Ni content. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM) studies show a modification of the surface morphology upon Ni substitution. Magnetic measurements disclose that the ferrimagnetic Curie temperature (T C) of the CoCr2O4 in thin film grown on MgAl2O4 (100) and MgO (100) substrates were found to be 100.6 ± 0.5 K and 93.8 ± 0.2 K, respectively. With Ni substitution the T C values were found to be enhanced to 104.5 ± 0.4 K for MgAl2O4 (100) and 108.5 ± 0.6 K for MgO (100) substrates. X-ray photoelectron spectroscopy (XPS) suggests Cr3+ oxidation states in the films, while Co ions are present in a mixed Co2+/Co3+ oxidation state. The substitution of Ni at Co site significantly modifies the line shape of the core level as well as the valence band. Ni ions are also found to be in a mixed 2+/3+ oxidation state. O 1s core level display asymmetry related to possible defects like oxygen vacancies in the films.
RESUMO
We have measured the antiferromagnetic spin-density-wave (SDW) order in Cr/Cr(97.5)Mn2.5(001) superlattices. The Mn doping creates a high Néel temperature layer that confines the incommensurate SDW order within the Cr layers. With temperature cycling we observe a transition from commensurate to incommensurate SDW order and discrete changes in the SDW period. We find that these transitions show significant hysteresis (up to 75 K) when the number of SDW nodes within the Cr layer changes by an odd number, while there is no hysteresis for changes of an even number of nodes. This results from the competition between maintaining the spin structure at the interfaces and introducing a spin slip at the nodes of the Cr SDW.
