Temperature dependence of the magnetic anisotropy of metallic Y-Ba-Cu-O single crystals in the normal phase

The magnetic anisotropy measurements of metallic Y-Ba-Cu-O compounds in the normal phase reveal a temperature-dependent diamagnetic component of the susceptibility that increases with decreasing temperature. The temperature variation of the susceptibility anisotropy and its total change do not seem to be much affected by the presence of the superconductivity at some lower temperature and could not be accounted for by superconducting fluctuations. Rather, the data remind one of the behavior of some quasi-two-dimensional metals with anisotropic Fermi surfaces, reflecting the properties of the low-energy excitations in the normal phase. The anisotropy measurements above the bulk superconducting transition temperature Tc reveal the nonlinear effects, which are due to the onset of superconductivity in disconnected grains. The existence of a two-step transition, typical for granular superconductors, should be taken into consideration if the normal-phase susceptibility data are compared with the theoretical predictions in the vicinity of Tc

The phase diagram of heavy fermions with Cerium and Europium ions

Doniach phase diagram of heavy fermions with Ce and Eu ions is explained by the scaling solution of the Anderson model. At high temperatures, where the rear earth ions behave as nearly independent local moments (LM) the system has a large paramagnetic entropy and its properties are defined by Kondo temperature, $T_K(p)$, where $p$ is the external parameter, like pressure or doping. For a given $T_K(p)$, the scaling law allows an estimate of the pressure or doping dependence of the coupling constant which is then used to find the dependence of the RKKY temperature $T_{RKKY}(p)$ and N\'eel temperature $T_N(p)$ on the control parameter. The competition between the on-site Kondo coupling and the off-site RKKY coupling determines the mechanism by which the system removes the paramagnetic entropy at low temperatures. The pressure-induced change of the ground state is explained by the differences in the functional form of $T_K(p)$ and $T_{RKKY}(p)$. Our theoretical results capture the main features shown by the Doniach diagram of CeRu$_2$Ge$_2$, CeCu$_2$(Ge$_{1-x}$Si$_{x})_2$ or EuCu$_2$(Ge$_{1-x}$Si$_{x})_2$.Comment: 6 pages, 2 figure

Kondo effect in Ce(x)La(1-x)Cu(2.05)Si(2) intermetallics

The magnetic susceptibility and susceptibility anisotropy of the quasi-binary alloy system Ce(x)La(1-x)Cu(2.05)Si(2) have been studied for low concentration of Ce ions. The single-ion desc ription is found to be valid for x < 0.1. The experimental results are discussed in terms of t he degenerate Coqblin-Schrieffer model with a crystalline electric field splitting Delta = 330 K. The properties of the model, obtained by combining the lowest-order scaling and the pertur bation theory, provide a satisfactory description of the experimental data down to 30 K. The e xperimental results between 20 K and 2 K are explained by the exact solution of the Kondo mode l for an effective doublet.Comment: 11 pages, 13 Postscript figures, 1 tabl

Kendala-kendala yang Dihadapi Siswa Menengah Atas (SMA) Selama Melakukan Proses Pembelajaran Berbasis Online (Daring)saat Pandemi Covid-19 di Kabupaten Tanah Datar

Pandemi Covid-19 membuat siswa harus melakukan proses pembelajaran secara online. Penelitian ini bertujuanuntuk mengetahuimasalahyang dialami oleh siswa saat melakukan proses belajar secara online (daring) sehingga siswa merasa cemas dan tertekan. Penelitian ini menggunakan metode kualitatif dengan melibatkan 47 (laki-laki= 9, perempuan= 38) responden yang merupakan siswa SMA sebanyak 39, SMK sebanyak 2, dan MA sebanyak 6 responden di Kabupaten Tanah Datar. Pengambilan data menggunakan Google Form yang berisi pertanyaan berupa survey tentang pembelajaran daring dan pertanyaan terbuka tentang pertanyaan yang disusun untuk mengetahui permasalahan apa saja yang dialami ketika melakukan pembelajaran daring yang memicu munculnya kecemasan beserta cara mengatasi permasalahan tersebut. Hasil yang ditemukan adalah terdapat beberapa faktor yang menjadi pemicu munculnya kecemasan siswa selama melakukan pembelajaran daring. Faktor tersebut yaitu susahnya jaringan internet dan kesulitan memahami materi yang diberikan oleh guru