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Register a new userHigh-field magnetization and magnetoresistance of the $A$-site ordered perovskite oxide CaCu$_{3}$Ti$_{4-x}$Ru$_{x}$O$_{12}$~($0 le x le 4$)
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We have measured high-field magnetization and magnetoresistance of polycrystalline samples of the A-site ordered perovskite CaCu3Ti4-xRuxO12 (x=0 - 4) utilizing a non-destructive pulsed magnet. We find that the magnetization for x=0.5, 1.0 and 1.5 is nonlinear, and tends to saturate in high fields. This is highly nontrivial because the magnetization for x=0 and 4 is linear in external field up to the highest one. We have analyzed this field dependence based on the thermodynamics of magnetic materials, and propose that the external fields delocalize the holes on the Cu2+ ions in order to maximize the entropy. This scenario is qualitatively consistent with a large magnetoresistance of -70% observed at 4.2 K at 52 T for x=1.5.
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By means of photoemission and x-ray absorption spectroscopy, we have studied the electronic structure of (Ni,Zn,Fe,Ti)$_{3}$O$_{4}$ thin films, which exhibits a cluster glass behavior with a spin-freezing temperature $T_f$ of $sim 230$ K and photo-induced magnetization (PIM) below $T_f$. The Ni and Zn ions were found to be in the divalent states. Most of the Fe and Ti ions in the thin films were trivalent (Fe$^{3+}$) and tetravalent (Ti$^{4+}$), respectively. While Ti doping did not affect the valence states of the Ni and Zn ions, a small amount of Fe$^{2+}$ ions increased with Ti concentration, consistent with the proposed charge-transfer mechanism of PIM.
We report measurements of the magnetic penetration depth $lambda$ in single crystals of Pr(Os$_{1-x}$Ru$_{x}$)$_{4}$Sb$_{12}$ down to 0.1 K. Both $lambda$ and superfluid density $rho_{s}$ exhibit an exponential behavior for the $x$$geq$0.4 samples, going from weak ($x$=0.4,0.6), to moderate, coupling ($x$=0.8). For the $x$$leq$0.2 samples, both $lambda$ and $rho_{s}$ vary as $T^{2}$ at low temperatures, but $rho_{s}$ is s-wave-like at intermediate to high temperatures. Our data are consistent with a three-phase scenario, where a fully-gapped phase at $T_{c1}$ undergoes two transitions: first to an unconventional phase at $T_{c2}$$lesssim$$T_{c1}$, then to a nodal low-$T$ phase at $T_{c3}$$<$$T_{c2}$, for small values of $x$.
Lutetium dodecaboride LuB12 is a simple weak-coupling BCS superconductor with critical temperature Tc = 0.42 K, whilst ZrB12 is a strong-coupling BCS superconductor with the highest critical temperature Tc = 6.0 K among this group of materials. In case of lutetium substitution by zirconium ions in LuB12 the crossover from weak- to strong-coupling superconductor can be studied. We have investigated the evolution of critical temperature Tc and critical field Hc in high-quality single crystalline superconducting samples of Lu(1-x)Zr(x)B12 (0 =< x =< 0.45) by measuring magnetic ac susceptibility between 1 K and 50 mK. To obtain this kind of experimental data, a new susceptometer was designed, constructed and tested, which can work in a wide temperature range of 0.05 K - 3 K in 3He-4He dilution refrigerator. The measurements with this new susceptometer revealed how Tc(x) and Hc(x) increases with increasing concentration of zirconium in Lu(1-x)Zr(x)B12 solid solutions as well as how their superconducting phase diagram develops.
We compute by hand all quadratic homogeneous polynomial maps $H$ and all Keller maps of the form $x + H$, for which ${rm rk} J H = 3$, over a field of arbitrary characteristic. Furthermore, we use computer support to compute Keller maps of the form $x + H$ with ${rm rk} J H = 4$, namely: $bullet$ all such maps in dimension $5$ over fields with $frac12$; $bullet$ all such maps in dimension $6$ over fields without $frac12$. We use these results to prove the following over fields of arbitrary characteristic: for Keller maps $x + H$ for which ${rm rk} J H le 4$, the rows of $J H$ are dependent over the base field.
We have systematically studied the magnetic properties of chromium chalcogene compounds FeCr$_2$Se$_{4-x}$Te$_x$. The FeCr2Se4 undergoes antiferromagnetic ordering below 222 K. Substitution of tellurium lowers the antiferromagnetic ordering temperature and leads to short range ferromagnetic cluster behavior towards the tellurium end. Change over from antiferromagnetic to ferrimagnetic like behavior is also reflected in the corresponding transformation from semiconducting to metallic transport behavior. There is a large variation in the Curie-Weiss temperature, effective magnetic moment and ordering temperature (TN / TC) with Te substitution. The electronic band structure calculations suggest antiferromagnetic and ferrimagnetic ground state for the FeCr2Se4 and FeCr2Te4 respectively.
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