Spin–glass Magnetism in RFeTi2O7 (R=Lu and Tb) Compounds

AbstractThe compounds RFeTi2O7 (R=Lu and Tb) crystallize at room temperature in centrosymmetric orthorhombic space group Pcnb. There are five non-equivalent positions of the iron ions: the two positions, Fe’ and Fe”, in the octahedron consisting of the Fe’ tetrahedron and Fe” five-vertex polyhedron and the three positions, Fe1, Fe2 and Fe3 in the mixed Fe-Ti octahedra [1]. The populations of the mixed Fe-Ti sites are different. The crystal structure features lead to atomic disorder in the distribution of the magnetic ions in this compound. From low temperature heat capacity, magnetization and frequency dependent ac susceptibility we conclude that both compounds undergo a spin glass transition at TSG=4.5 and 6K for R =Lu and Tb, respectively. Since Lu is not magnetic, in RFeTi2O7 the spin glass behavior is caused by the disordered distribution of the magnetic Fe3+ ions in the different crystallographic positions. The substitution of the magnetic and highly anisotropic Tb ion instead of Lu increases TSG because of the additional Tb-Fe exchange interaction, while the critical exponent of the frequency dependence on temperature hardly varies. The spin glass behavior in these crystalline compounds is caused by the presence of competitive interactions that lead to frustration

Revolutionizing physics: a comprehensive survey of machine learning applications

In the context of the 21st century and the fourth industrial revolution, the substantial proliferation of data has established it as a valuable resource, fostering enhanced computational capabilities across scientific disciplines, including physics. The integration of Machine Learning stands as a prominent solution to unravel the intricacies inherent to scientific data. While diverse machine learning algorithms find utility in various branches of physics, there exists a need for a systematic framework for the application of Machine Learning to the field. This review offers a comprehensive exploration of the fundamental principles and algorithms of Machine Learning, with a focus on their implementation within distinct domains of physics. The review delves into the contemporary trends of Machine Learning application in condensed matter physics, biophysics, astrophysics, material science, and addresses emerging challenges. The potential for Machine Learning to revolutionize the comprehension of intricate physical phenomena is underscored. Nevertheless, persisting challenges in the form of more efficient and precise algorithm development are acknowledged within this review

Spin–glass magnetism in RFeTi2O7 (R=Lu and Tb) compounds

20th International Conference on Magnetism.The compounds RFeTi2O7 (R=Lu and Tb) crystallize at room temperature in centrosymmetric orthorhombic space group Pcnb. There are five non-equivalent positions of the iron ions: the two positions, Fe’ and Fe”, in the octahedron consisting of the Fe’ tetrahedron and Fe” five-vertex polyhedron and the three positions, Fe1, Fe2 and Fe3 in the mixed Fe-Ti octahedra [1]. The populations of the mixed Fe-Ti sites are different. The crystal structure features lead to atomic disorder in the distribution of the magnetic ions in this compound. From low temperature heat capacity, magnetization and frequency dependent ac susceptibility we conclude that both compounds undergo a spin glass transition at TSG=4.5 and 6 K for R =Lu and Tb, respectively. Since Lu is not magnetic, in RFeTi2O7 the spin glass behavior is caused by the disordered distribution of the magnetic Fe3+ ions in the different crystallographic positions. The substitution of the magnetic and highly anisotropic Tb ion instead of Lu increases TSG because of the additional Tb-Fe exchange interaction, while the critical exponent of the frequency dependence on temperature hardly varies. The spin glass behavior in these crystalline compounds is caused by the presence of competitive interactions that lead to frustration.The financial support of the Spanish MINECO MAT2011-23791, MAT2014-53921-R and Aragonese DGA-IMANA E34 projects is acknowledged.Peer Reviewe

Comparative investigations of the crystal structure and photoluminescence property of eulytite-type Ba3Eu(PO4)3 and Sr3Eu(PO4)3

In this study, the Ba3Eu(PO4)3 and Sr3Eu(PO4)3 compounds were synthesized and the crystal structures were determined for the first time by Rietveld refinement using powder X-ray diffraction (XRD) patterns. Ba3Eu-(PO4)3 crystallizes in cubic space group I4¯3d, with cell parameters of a = 10.47996(9) Å, V = 1151.01(3) Å3 and Z = 4; Ba2+ and Eu3+ occupy the same site with partial occupancies of 3/4 and 1/4, respectively. Besides, in this structure, there exists two distorted kinds of the PO4 polyhedra orientation. Sr3Eu(PO4)3 is isostructural to Ba3Eu(PO4)3 and has much smaller cell parameters of a = 10.1203(2) Å, V = 1036.52(5) Å3. The bandgaps of Ba3Eu(PO4)3 and Sr3Eu(PO4)3 are determined to be 4.091 eV and 3.987 eV, respectively, based on the UV–Vis diffuse reflectance spectra. The photoluminescence measurements reveal that, upon 396 nm n-UV light excitation, Ba3Eu(PO4)3 and Sr3Eu(PO4)3 exhibit orange-red emission with two main peaks at 596 nm and prevailing 613 nm, corresponding to the 5D0 → 7F1 and 5D0 → 7F2 transitions of Eu3+, respectively. The dynamic disordering in the crystal structures contributes to the broadening of the luminescence spectra. The electronic structure of the hosphates was calculated by the first-principles method. The analysis elucidats that the band structures are mainly governed by the orbits of phosphorus, oxygen and europium, and the sharp peaks of the europium f-orbit occur at the top of the valence bands

The modulated structure and frequency upconversion properties of CaLa2(MoO4)4:Ho3+/Yb3+ phosphors prepared by microwave synthesis

CaLa2_x(MoO4)4:Ho3+/Yb3+ phosphors with the doping concentrations of Ho3+ and Yb3+ (x = Ho3+ + Yb3+, Ho3+ = 0.05; Yb3+ = 0.35, 0.40, 0.45 and 0.50) have been successfully synthesized by the microwave sol-gel method. The modulated and averaged crystal structures of CaLa2_x(MoO4)4:Ho3+/Yb3+ molybdates have been found by the Rietveld method, and the upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after the heat-treatment at 900 °C for 16 h, showed a highly crystallized state. Under the excitation at 980 nm, CaLa2_x(MoO4)4:Ho3+/Yb3+ particles exhibited strong 545 and 655 nm emission bands in the green and red regions. When the Yb3+ :Ho3+ ratios are 9 : 1 and 10: 1, the UC intensity of CaLai.5(MoO4)4:Yb045/Ho0.05 and CaLai45(MoO4)4:Yb0.50/Ho0.05 particles is the highest for different bands. The CIE coordinates calculated for CaLa2_x(MoO4)4:Ho3+/Yb3+ phosphors are related to the yellow color field. The Raman spectrum of undoped CaLa2(MoO4)4 has revealed about 13 narrow lines. The strongest band observed at 906 cirT1 was assigned to the n1 symmetric stretching vibration of MoO4 tetrahedra. The spectra of the samples doped with Ho and Yb, as obtained under the 514.5 nm excitation, were dominated by Ho3+ luminescence over the wavenumber range of >700 cm-1 preventing the recording of the Raman spectra