Magnetic behavior of nanocrystalline LaMn2Ge2

纳米晶准一维 spin-1/2 反铁磁体 Sr21Bi8Cu2(CO3)2O41 中随机单态的形成

Formation of random singlets in the nanocrystalline quasi-one-dimensional spin-1/2 antiferromagnet Sr21Bi8Cu2(CO3)2O41

本研究测量了纳米晶准一维 spin-1/2 反铁磁体 Sr21Bi8Cu2(CO3)2O41 的比热与磁化率，发现其主导的随机单态自旋对分布偏离传统理论，揭示了由纳米晶有限尺寸导致的独特交换相互作用依赖性。

Magnetocaloric effect in nano- and polycrystalline manganite $La_{0.7}Ca_{0.3}MnO_3$

$La_{0.7}Ca_{0.3}MnO_3$ samples were prepared in nano- and polycrystalline forms by sol-gel and solid state reaction methods, respectively, and structurally characterized by synchrotron X-ray diffraction. The magnetic properties determined by ac susceptibility and dc magnetization measurements are discussed. The magnetocaloric effect in this nanocrystalline manganite is spread over a broader temperature interval than in the polycrystalline case. The relative cooling power of the poly- and nanocrystalline manganites is used to evaluate a possible application for magnetic cooling below room temp…

Giant negative thermal expansion covering room temperature in nanocrystalline GaNxMn3

Materials with negative thermal expansion (NTE), which contract upon heating, are of great interest both technically and fundamentally. Here, we report giant NTE covering room temperature in mechanically milled antiperovksite GaNxMn3 compounds. The micrograin GaNxMn3 exhibits a large volume contraction at the antiferromagnetic (AFM) to paramagnetic (PM) (AFM-PM) transition within a temperature window (ΔT) of only a few kelvins. The grain size reduces to ~ 30 nm after slight milling, while ΔT is broadened to 50K. The corresponding coefficient of linear thermal expansion (α) reaches ~ -70 ppm/K,…

Colossal enhancement of electrical conductivity in Y2Ir2O7 nanoparticles

We present a comparative study of the magnetic and electrical properties of polycrystalline and nanocrystalline Y2Ir2O7, the latter prepared using a new chemical route. We find that reduction in particle size leads to enhanced ferromagnetism and orders of magnitude enhancement of electrical conductivity in the nanocrystalline sample. Based on x ray photoelectron spectroscopy and x ray absorption near edge structure spectroscopy results, the phenomenon is attributed to the increased fraction of pentavalent oxidation state of Iridium and the resulting increase in double exchange interaction alon…

Eu valence transition behavior in the nano form of EuPd2Si2

The compound EuPd2Si2 is a well-known valence-fluctuating compound with a largest variation of Eu valence in a narrow temperature interval (around 150 K). The ball-milled form of this compound was investigated to understand the Eu valence behavior in the nanoform. The compound is found to retain the ThCr2Si2-type tetragonal structure after ball-milling leading to a reduction in particle size, typically falling in the range 10 - 100 nm. We find that there is a qualitative change in the temperature dependence of magnetic susceptibility for such small particles, with respect to that known for bul…

Magnetic behavior of curium dioxide with non-magnetic ground state

In order to understand magnetic behavior observed in CmO$_2$ with non-magnetic ground state, we numerically evaluate magnetic susceptibility on the basis of a seven-orbital Anderson model with spin-orbit coupling. Naively we do not expect magnetic behavior in CmO$_2$, since Cm is considered to be tetravalent ion with six $5f$ electrons and the ground state is characterized by $J$=0, where $J$ is total angular momentum. However, there exists magnetic excited state and the excitation energy is smaller than the value of the Landé interval rule due to the effect of crystalline electric field poten…

Polar Behavior in a Magnetic Perovskite Via A-Site Disorder

We elucidate a mechanism for obtaining polar behavior in magnetic perovskites based on A-site disorder and demonstrate this mechanism by density functional calculations for the double perovskite (La,Lu)MnNiO$_6$ with Lu concentrations at and below 50%. We show that this material combines polar behavior and ferromagnetism. The mechanism is quite general and may be applicable to a wide range of magnetic perovskites.

Insight into the magnetic behavior of Sr$_2$IrO$_4$:A spontaneous magnetization study

Sr$_2$IrO$_4$ is a weak ferromagnet where the spin arrangement is canted anti-ferromagnetic (AF). Moreover, the spin-structure coupling plays and important role in magnetic behavior of Sr$_2$IrO$_4$. In this concern the magnetization under zero applied field i.e. spontaneous magnetization would be interesting to study and would give insight into the novel magnetic behavior of Sr$_2$IrO$_4$. Sophisticated techniques like neutron diffraction, $μ$ \textit{SR} etc has been used to understand the magnetic behavior of Sr$_2$IrO$_4$ under zero applied field. To understand the magnetic behavior we hav…

Cross-over behavior of disordered interacting two-dimensional electron systems in a parallel magnetic field

We present analysis of the cross-over behavior of disordered interacting two-dimensional electron systems in the parallel magnetic field. Using the so-called cross-over one-loop renormalization group equations for the resistance and electron-electron interaction amplitudes we qualitatively explain experimentally observed transformation of the temperature dependence of the resistance from a reentrant (nonmonotonic) behavior in relatively weak fields into an insulating-type behavior in stronger fields.

Magnetic behavior of bulk and fine particles of RCr2Si2C (R = La, Ce)compounds: possible magnetic ordering from Cr

The magnetic behavior of the quaternary compounds, RCr2Si2C (R = La, Ce), has been investigated by magnetization (M) and heat-capacity (C) measurements (1.8-300 K) in the bulk polycrystals and nano forms (<1 μm) obtained by high-energy balling. Our finding is that Cr appears to exhibit magnetic ordering of an itinerant type at low temperatures (<20 K) in the bulk form, as inferred from a combined look at all the data. The magnetic ordering gets gradually suppressed with increasing milling time. Evidence for a mixed-valence state of Ce for the bulk form is obtained from the tendency of magnetic…