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We observe multiple step-like jumps in a Dy-Fe-Ga-based ferrimagnetic alloy in its magnetic hysteresis curve at 2 K. The observed jumps have a stochastic character with respect to their magnitude and the critical field of occurrence, and the jumps do not show any temporal effect. The jump size distribution follows a power law variation indicating the scale invariance nature of the jumps. We have invoked a simple two-dimensional random bond Ising-type spin system to model the dynamics. Our computational work can qualitatively reproduce the jumps and their scale invariant character. It also elucidates that the flipping of antiferromagnetically coupled Dy and Fe clusters is responsible for the observed discrete avalanche-like features in the hysteresis loop. These characteristics indicate that the present phenomenon can be well described within the realm of self-organized criticality, 12 pages, 13 figures

A facile sol–gel approach to prepare composites of nanosilica glass containing dual transition metal oxides with compositions xCoO·(20 − x)NiO·80SiO2 comprising x values 5 (NC-1), 10 (NC-2) and 15 (NC-3) within hexagonal pores of SBA-15 template has been demonstrated. The synergistic effect of dual transition metal oxide ions on MD properties and crossover of positive and negative magnetoconductance phenomena were observed in these nanocomposite systems. The physical origin of magnetoconductance switching is explained based on the factors: nanoconfinement effect, wave-function shrinkage and spin polarized electron hopping. DFT calculations were performed to understand the structural correlation of the nanoconfined system. The static (dc) and dynamic (ac) responses of magnetization revealed the spin-glass behaviour of the investigated samples. Both scaling law and Vogel–Fulcher law provide a satisfactory fit to our experimental results which are considered as a salient feature of the spin-glass system. Our studies indicate the possibilities of fabricating magnetically controlled multifunctional devices.

Glasses having compositions xNa2O·10P2O5·(100–(10+x))SiO2, with x having values of 20 and 35, were synthesized by a facile sol–gel technique within a mesoporous silica (SBA-15) template. Nanocrysta...

We report here the electrical transport and magnetic properties of the newly synthesized quaternary Heusler compounds CoFeTiSn and CoFeVGa. Our study indicates a striking change in the electronic transport properties of CoFeTiSn as the system undergoes the paramagnetic to ferromagnetic transition. While the sample shows an activated semiconducting behaviour in the paramagnetic phase, it turns abruptly to a metallic phase with the onset of ferromagnetic transition. We have compared the system with other Heusler compounds showing similar anomaly in transport, and it appears that CoFeTiSn has much similarities with the Fe 2 VAl compound having pseudogap in the paramagnetic phase. On the other hand, CoFeVGa shows a semiconducting behaviour from high temperature to 90 K. On cooling below 90 K, a broad hump like feature is observed. Both the compositions show negative Seebeck coefficient varying linearly with temperature. The value of the Seebeck coefficient of CoFeTiSn is comparable to that of many Heusler alloys identified as potential thermoelectric materials.

We report a characteristic spin-glass-like behavior in Sr3NiSb2O9, as confirmed from the low-field dc magnetometry and ac susceptibility measurements. The memory effects in the dc magnetometry exhibit similar characteristic features of the spin-glass systems. The ac susceptibility measurements provide that the frequency dependent peak-shift follows the conventional Vogel-Fulcher and dynamical scaling laws with the characteristic relaxation time to be ∼ 10−14 s. This relaxation time fits in the recommended range of ∼ 10 − 12 − 10 − 14 s for the classical spin-glasses. Low temperature synchrotron diffraction studies point to the strong magnetoelastic coupling close to the spin-glass-like transition. The transition is found to be associated with the step-like anomalous lattice contraction. Possible origin of magnetic frustration leading to the spin-glass ground state is discussed by correlating the microstructural results, as obtained from the analysis of synchrotron diffraction studies.

The rare-earth intermetallic compound Ho

The rare-earth intermetallic compound Ho$_5$Sn$_3$ demonstrates fascinating magnetic properties which include temperature-driven multiple magnetic transitions and field driven metamagnetism. We address the magnetic character of this exciting compound through a combined experimental and theoretical studies. Ho$_5$Sn$_3$ orders antiferromagnetically below $~28$ K, and shows further spin reorientation transitions at 15 K and 12 K. We observe a sizable amount of low-temperature magnetocaloric effect in Ho$_5$Sn$_3$ with a maximum value of entropy change $\Delta S$ = -9.5 JKg$^{-1}$K$^{-1}$ for an applied field of $H$ = 50 kOe at around 30 K. The field hysteresis is almost zero above 15 K where magneto-caloric effect is important. Interestingly, $\Delta S$ is found to change its sign from positive to negative as the temperature is increased above about 8 K, which can be linked to the multiple spin reorientation transitions. The signature of the metamagnetism is visible in the $\Delta S$ versus $H$ plot. The magnetic ground-state, obtained from the density functional theory based calculation, is susceptible to the effective Coulomb interaction ($U_{\rm eff}$) between electrons. Depending upon the value of $U_{\rm eff}$, the ground-state can be ferromagnetic or antiferromagnetic. The compound shows large relaxation (14\% change in magnetization in 60 min) in the field cooled state with a logarithmic time variation, which may be connected to the competing magnetic ground-states observed in our theoretical calculations. The competing magnetic ground-states is also evident from the small value of the paramagnetic Curie-Weiss temperature., Comment: 10 pages, 6 figures

Heusler compounds are a large group of intermetallic compositions with versatile material properties. In recent times, they are found to be important for their practical applications in the fields of spintronics and shape memory effect. Interestingly, their physical properties can be easily tuned by varying the valence electron concentration through proper doping and substitution. Empirical laws concerning the valence electron concentration, such as Slater-Pauling or Hume-Rothery rules are found to be useful in predicting their electronic, magnetic and structural properties quite accurately. Electrical transport measurements are simple laboratory-based techniques to gather a handful of information on the electronic properties of metals and semiconductors. The present review aimed to provide a comprehensive view of the transport in 3dand 4dtransition metal-based bulk Heusler compositions. The main emphasis is given on resistivity, magnetoresistance, Hall effect, thermopower and spin-dependent transport in spintronics devices. The review primarily focuses on magnetic Heusler compounds and alloys, albeit it also addresses several non-magnetic materials showing superconductivity or large thermopower.

Magnetic transition element doping in topological insulators, which breaks the time-reversal symmetry, gives rise to the diverse range of exotic consequences, though proper understanding of the magnetic order has rarely been attempted by using any microscopic experiments. We report the occurrence of the magnetic order in (${\mathrm{Sb}}_{0.95}{\mathrm{Cr}}_{0.05}{)}_{2}{\mathrm{Te}}_{3}$ using the muon spin relaxation studies. The asymmetry curve at low temperature ($T$) shows an evidence of a damped oscillation, providing a clue about the internal magnetic field (${H}_{\mathrm{int}}$), which follows ${H}_{\mathrm{int}}(T)={H}_{\mathrm{int}}(0){[1\ensuremath{-}T/{T}_{C}]}^{\ensuremath{\beta}}$ with ordering temperature ${T}_{C}\ensuremath{\approx}6.1$ K and critical exponent $\ensuremath{\beta}\ensuremath{\approx}0.22$. The critical exponent is close to the two-dimensional XY-type interaction. The magnetization curves at low $T$ exhibit a ferromagnetic behavior at low field ($H$) and the de Haas--van Alphen (dHvA) effect at high $H$. The analysis of the dHvA oscillation proposes the charge carrier that acts like a massive Dirac fermion. The Berry phase, as obtained from the Landau-level fan diagram, suggests a surface state gap at the Dirac point. The complex electronic structure is discussed by correlating the magnetic order attributed to the Cr doping in ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$.

The rhombohedral distortion-driven occurrence of the spontaneous electric polarization at a reasonably high temperature $(T)$ and an exchange bias (EB) effect below the antiferromagnetic (AFM) N\'eel temperature $({T}_{N})$ are revealed in ${\mathrm{ZnFe}}_{2}{\mathrm{O}}_{4}$. We observe the magnetic memory effect, suggesting a cooperative glassy magnetic state below ${T}_{N}$. The phase separation between the long-range AFM and the glassy magnetic component leads to the EB effect below ${T}_{N}$. The synchrotron diffraction studies confirm a structural transition to a polar $R3m$ structure from the cubic spinel structure, involving a strong rhombohedral distortion. This distortion correlates with the occurrence of the spontaneous electric polarization $(P)$ below $\ensuremath{\sim}110$ K $({T}_{\text{FE}1})$, which is accompanied by a short-range order (SRO). The $P$-value enhances further due to an additional rhombohedral distortion below ${T}_{N}$. A considerable magnetoelectric (ME) coupling is detected below ${T}_{\text{FE}1}$. The increase of $P$ is $\ensuremath{\sim}7.2$% for 5 T at the liquid nitrogen temperature. There has been a fundamental interest among the community in the unique result of the occurrence of ferroelectric (FE) order coexisting with SRO and having a significant ME coupling, which is accompanied by a strong rhombohedral structural distortion analogous to that observed in ${\mathrm{BiFeO}}_{3}$.

The complex metallic alloy ${\mathrm{Mn}}_{3}\mathrm{In}$ has recently attracted attention for being a probable candidate for the fully compensated half-metallic ferrimagnet. The compound is associated with a rather unusual negative coefficient of resistivity approximately above the ferrimagnetic, ${T}_{C}=80\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Our investigation indicates that that the ground state of the alloy is spin-glass like, which possibly coexists with the ferrimagnetic state. The carrier density obtained from the Hall-effect measurement shows a jump below ${T}_{C}$; afterward, it gradually increases with lowering temperature and shows a saturating tendency at the lowest temperature. The electronic structure calculations indicate that, at the Fermi energy, dominant contributions come from minority-spin channels with larger bandwidth. In contrast, very weak but nonzero states arise from the majority-spin channel, and half metallicity can be ruled out. The calculations also found that the antiferromagnetic alignment of Mn spins with nonzero resultant magnetic moment confirms the ferrimagnetic nature consistent with the experimental results. The high-temperature phase with negative temperature coefficient of resistivity can be related to the localization of charge carriers through electron-phonon interactions.

The quaternary Heusler compound NiFeTiSn can be considered to be derived from the exotic pseudogap-compound Fe2TiSn by the replacement of one Fe atom by Ni. In contrast to Fe2TiSn, which shows a disorder-induced ferromagnetic phase, the ground state of NiFeTiSn is antiferromagnetic with the signature of spin canting. Interestingly, NiFeTiSn shows a Griffiths-like phase characterized by isolated ferromagnetic clusters before attaining the antiferromagnetic state. The Griffiths-like phase is possibly associated with the antisite disorder between Fe and Ti sites as evident from our powder X-ray diffraction study. The compound also shows rather an unusual temperature dependence of resistivity, which can be accounted for by the prevailing structural disorder in the system. NiFeTiSn turned out to be a rare example where a Griffiths-like phase is observed in a semiconducting 3d transition metal-based intermetallic compound with an antiferromagnetic ground state., Comment: 12 pages, 9 figures

Silver nanowires of diameter ~ 5 nm were grown within thick films (0.6 µm thickness) of sol–gel-derived silica-based glasses of composition xAg2O(1 − x)SiO2; x having values of 30 and 40, respectively, by an electrodeposition method. By applying suitable voltage pulses to the composites, interrupted silver nanowires were produced with lengths having values in the range 4000–5000 nm. The samples exhibited dielectric constant with values of the order of 105 and a low dielectric loss (~ 0.01). The dielectric constant values calculated by using Rice–Bernasconi model which originated from Gorkov–Eliashberg theory of metallic nanoparticles were in satisfactory agreement with the experimental results. The present work not only provides strong evidence for the basis of Rice–Bernasconi model but also opens up a simple method to synthesize high dielectric constant materials which will be useful in fabricating devices for very large-scale integration applications, among others.

We observe significant exchange-bias effect below ∼ 76 K in antiferromagnetic YbBaCo4O7. Exchange-bias field ( H E ) is ∼ 10 kOe for 50 kOe cooling-field ( H c o o l ) at 4 K. The H E increases considerably with H c o o l associated with the nominal increase of coercivity ( H C ) . Low H C provides high value of H E / H C ( ∼ 15) at 4 K. High H E / H C ratio and nominal increase of H C are appealing. The results suggest robust EB effect associated with the minimal occurrence of inhomogeneous micro-domains, which is potential for the applications. Magnetic phase separation between antiferromagnetic components with k 1 = (0, 0, 0) and k 2 = (1/2, 0, 0) propagation vectors of the P b n 2 1 space group is correlated with the exchange-bias effect.

A new ternary compound Sm 2 Ni 0.87 Si 2.87 , belonging to intermetallic R 2 TX 3 family ( R = rare-earth, T = transition metals, X = Si, Ge, etc. ), could be synthesized in single phase only by the deliberate introduction of lattice vacancies in the Ni and Si sites. The detailed studies of heat capacity as well as dc and ac magnetization including different non-equilibrium dynamical behaviour, viz. , aging effect, temperature and field dependent magnetic relaxation and magnetic memory effect establish the compound to be a cluster-glass material having a spin freezing temperature ∼6.6 K. To understand the nature of the glassy phase, experimental results have been analysed using a few different theoretical models and found that the observed magnetic memory effect favours the hierarchical model over the droplet model. Competing exchange interaction driven magnetic phase inhomogeneity could be further confirmed through exchange bias effect. The observed magnetic phase inhomogeneity has been attributed to random magnetic anisotropy that develops due to local environmental variations between the rare-earth ions.

Significant exchange bias effect is observed in the granular Ni1-xZnxO film prepared by sol-gel dip-coating technique on a silicon single crystal (100) substrate. Atomic force microscopy reveals the crystallite size which is commensurate with that obtained from the analysis of X-ray diffraction studies. Magnetization measurement reveals the blocked state of Ni0.95Zn0.05O below 155 K. On the other hand, the uncompensated spin is inferred for Ni0.97Zn0.03O from the low temperature up turn of the magnetization. The systematic shift of the magnetic hysteresis loop of Ni1-xZnxO film is measured in field cooled mode. This is the fingerprint of exchange bias (EB) effect which is found to depend strongly on x. The pinning mechanism at the interface between antiferromagnetic core and shell consisting of uncompensated spins in the granular Ni1-xZnxO film is proposed for interpreting the EB effect.

In this work, we report the successful synthesis of a new intermetallic compound Dy2Ni0.87Si2.95 forming in single phase only with a chemically disordered structure. The random distribution of Ni/Si and crystal defects create a variation in the local electronic environment between the magnetic Dy ions. In the presence of both disorder and competing exchange interactions driven magnetic frustration, originating due to c/a ∼ 1, the compound undergoes spin freezing behaviour below 5.6 K. In the non-equilibrium state below the spin freezing behaviour, the compound exhibits aging phenomena and magnetic memory effects. In the magnetically short-range ordered region, much above the freezing temperature, an unusual occurrence of considerable magnetic entropy change, −ΔSmaxM ∼ 21 J kg−1 K−1 with large cooling power RCP ∼ 531 J kg−1 and adiabatic temperature change, ΔTad ∼ 10 K for a field change of 70 kOe, is observed for this short range ordered cluster-glass compound without any magnetic hysteresis loss.

Near the paramagnetic to ferrimagnetic transition temperature, the dc magnetization data of two sulpho spinels, CoCr2S4 and FeCr2S4, are analyzed by the modified Arrott plot, the Kouvel-Fisher method, log M vs log H, and the scaling analysis. Critical exponents β = 0.3946 ± 0.0064, 0.421 ± 0.04, γ = 1.101 ± 0.004, 1.041 ± 0.015, and δ = 3.77 ± 0.06, 3.512 ± 0.14 are obtained around the critical temperature ∼ 224.4 K and 166.5 K for CoCr2S4 and FeCr2S4, respectively. Scaling analysis indicates that calculated critical exponents, as well as critical temperatures, are intrinsic to the systems. The values of critical exponents of CoCr2S4 are between those predicted for a three dimensional Heisenberg model and those predicted by mean field theory. Probably, the observed large spin-phonon coupling and magnetocrystalline anisotropy caused by Co ion may play the key role in this critical behavior of CoCr2S4. The critical exponents of FeCr2S4 are close to the mean field theory except for δ, which is higher than the theoretical value. The higher value of δ may arise due to the incomplete ferrimagnetic transition and presence of short range magnetic ordering above T C for FeCr2S4.

Magnetocaloric effect (MCE) in multiferroic cubic spinel MnCr2O4 (space group Fd (3) over barm, no. 227, cF56), has been investigated using dc magnetization studies. The values of maximum magnetic entropy change (Delta S-M(max)) and the adiabatic temperature change (Delta T-ad) are similar to 5.3 J kg(-1) K-1 and similar to 2 K, respectively, at similar to 42.8 K for the magnetic field change of 50 kOe. The dc magnetization data near the transition temperature were analyzed by the modified Arrott plots, the Kouvel-Fisher method, log M vs log H, and the scaling analysis. Critical exponents beta = 0.3932 +/- 0.0287, gamma = 1.0256 +/- 0.0239, and delta = 3.55 +/- 0.26 are obtained around the critical temperature similar to 42.88 K. The critical exponents are in excellent agreement with the single scaling equation of state M(H, is an element of) = is an element of(0: 3932 +/- 0: 0287) f(+/-)(H/is an element of(((0: 3932 +/- 0: 0287)+(1: 0256 +/- 0: 0239)))); with f(+) for T > 42.88 K, f(-) for T < 42.88 K, and is an element of = (T - 42.88)/42.88. At T = 42.88 K, the exponent d relates the magnetization with applied filed by M - H-(1/3: 55 +/- 0: 26) Scaling analysis shows that calculated critical exponents as well as critical temperature are intrinsic to the system. Theoretically, the value of b is close to 3D Heisenberg model, while values of c and d are close to those of the mean field model. So the values of critical exponents indicate that the critical behavior of MnCr2O4 cannot be described within the framework of existing universality classes and probably belong to a separate class. (C) 2017 Elsevier B.V. All rights reserved.

We report here the observation of the inverse exchange bias phenomenon in the ferrimagnetic double-perovskite ${\mathrm{Gd}}_{2}{\mathrm{CoRuO}}_{6}$. The compound crystallizes in a monoclinic structure (space group $P{2}_{1}/n$), and it undergoes long-range magnetic ordering below ${T}_{C}=60$ K. The ferrimagnetic state of the sample is manifested through magnetization reversal at low temperature. In order to corroborate the role of local structure on the magnetic properties of ${\mathrm{Gd}}_{2}{\mathrm{CoRuO}}_{6}$, we have performed a combined magnetization and x-ray absorption spectroscopy study on two different samples prepared through different cooling protocols (slow cooling and furnace cooling). Extended x-ray absorption fine-structure analysis indicates the presence of strong antisite disorder between Co and Ru in both samples. However, the slow-cooled sample shows completely random antisite disorder, whereas, small Co- and Ru-rich patches appear in the furnace-cooled sample. In both samples, a significant amount of mixed valency in Co and Ru ions is evident from our x-ray absorption near-edge structure. The antiparallel ordering along with different temperature dependence of the three magnetic sublattices, Gd, Co, and Ru, can be responsible for negative magnetization, whereas the inverse exchange bias effect can be attributed to the mixed interfacial coupling between adjacent magnetic nanoclusters. The difference in local structure can nicely be accounted for by the observed variations of the magnetic properties between two samples of ${\mathrm{Gd}}_{2}{\mathrm{CoRuO}}_{6}$.

We investigate the magnetic and dielectric properties of zircon-type DyVO4. The evidence of dielectric anomaly at the Jahn-Teller (JT) transition temperature (TD) in DyVO4 points a direct consequence of the onset of an electric polarization. We also report that the JT domain control gives rise to a remarkable magnetodielctric (MD) coupling, which is probably maximum in the RVO4 series. MD coupling scales linearly with the squared magnetization as described by the Ginzburg-Landau theory.

We report the high quality single crystal growth and X-ray diffraction characterization studies of bulk Sb1.95Cr0.05Te3 single crystals. Elemental analysis is confirmed by TEM EDX spectroscopy. Single crystal of Sb1.95Cr0.05Te3 is grown by modified Bridgman method. The diffraction peaks corresponding to {0, 0, 3} planes reveal the growth of crystal along the c-direction. X-ray diffraction analysis using Rietveld refinement verifies the phase purity and confirms that the material crystalizes in a trigonal structure with R- 3m space group.

We report the single crystal growth and X-ray diffraction characterization of bulk Bi1.8Sb0.2Te1.5Se1.5 single crystals. Single crystal of Bi1.8Sb0.2Te1.5Se1.5 was grown by modified Bridgman method. The diffraction peaks corresponding to {0, 0, 3} planes reveal the growth of crystal along the c-direction. Analysis of X-ray diffraction pattern using Rietveld refinement verifies the phase purity, and confirms rhombohedral structure with R-3m space group.

Lithium ion conduction in nanodimensional borosilicate glass with glass composition 30Li2O.7B2O3.63SiO2 within mesoporous alumina (MA) template was studied. Facile sol-gel in-situ process was adopted for the preparation of samples. Small angle x-ray scattering and TEM analysis affirm the mesoporous feature of our sample. High surface area (370 m2/g) of MA was determined from BET analysis. Surface morphology was studied using SEM. Alkali ion containing glass confined in ordered mesoporous template showed ∼4 orders of magnitude higher conductivity values than the corresponding bulk glass. The increase in conductivity was ascribed to the increase in free volume which provides unhindered ionic pathways. The nanocomposite showed a dc conductivity value ∼10−6 S • cm−1 at room temperature. Activation energy for nanocomposite was determined from Arrhenius equation and was found to be 0.28 eV. This nanocomposite may find potential applications in solid state ion battery operable at room temperature.

We observe a ferroelectric (FE) order in an unexplored ${\mathrm{CuCr}}_{2}{\mathrm{O}}_{4}$ with a reasonably high value of the FE Curie temperature $({T}_{\mathrm{FE}})$ at 170 K, which is also much higher than the magnetic ordering temperature. The systematic substitution of Jahn-Teller (J-T) active divalent Cu ion by a non-Jahn-Teller active divalent Co ion causes a systematic shift of ${T}_{\mathrm{FE}}$ from 170 K for $x=0$ to 146 K for $x=0.8$ in ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$. The values of electric polarization vary from 0.0665 $\ensuremath{\mu}{\mathrm{C}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}}^{\ensuremath{-}2}$ to 0.1704 $\ensuremath{\mu}{\mathrm{C}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}}^{\ensuremath{-}2}$, which is maximum for $x=0.6$, associated with the highest value of the coercivity. The synchrotron diffraction studies of the compounds with $x=0.2$ and 0.8 confirm that a structural transition to a polar $Ima2$ space group from the tetragonally distorted $I{4}_{1}/amd$ structure gives rise to the ferroelectricity. In all the members of ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$ series, the ${T}_{\mathrm{FE}}$ is observed at much higher temperature than the corresponding magnetic ordering temperatures $({T}_{N})$. These results are in contrast to that of the reported results of ${T}_{\mathrm{FE}}l{T}_{N}$ for the end member with $x=1$ or ${\mathrm{CoCr}}_{2}{\mathrm{O}}_{4}$, where the J-T active ${\mathrm{Cu}}^{2+}$ is absent. We propose that the J-T distortion in the entire series with $0\ensuremath{\le}x\ensuremath{\le}0.8$ holds the key, where interplay between the J-T distortion driven orbital order and the structural distortion correlates tuning of the ${T}_{\mathrm{FE}}$ in ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$.

The high-temperature ferroelectric order and a remarkable magnetoelectric effect driven by the magnetic field cooling are reported in ${R}_{2}{\mathrm{BaCuO}}_{5}\phantom{\rule{4pt}{0ex}}(R$ = Er, Dy, Sm) series. The ferroelectric (FE) orders are observed at much higher temperatures than their magnetic orders for all three members. The value of FE Curie temperature $({T}_{\mathrm{FE}})$ is considerably high as $\ensuremath{\sim}235$ K with the polarization value $(P)$ of $\ensuremath{\sim}1410\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}^{2}$ for a 4 kV/cm poling field in the case of ${\mathrm{Er}}_{2}{\mathrm{BaCuO}}_{5}$, whereas the values of ${T}_{\mathrm{FE}}$ and $P$ are also promising as $\ensuremath{\sim}232$ and $\ensuremath{\sim}992\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}^{2}$ for ${\mathrm{Dy}}_{2}{\mathrm{BaCuO}}_{5}$, and $\ensuremath{\sim}184$ K and $\ensuremath{\sim}980\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}^{2}$ for ${\mathrm{Sm}}_{2}{\mathrm{BaCuO}}_{5}$. The synchrotron diffraction studies of ${\mathrm{Dy}}_{2}{\mathrm{BaCuO}}_{5}$ confirm a structural transition at ${T}_{\mathrm{FE}}$ to a polar $Pna{2}_{1}$ structure, which correlates the FE order. An unusual magnetoelectric coupling is observed below the $R$ order for Er and Dy compounds and below the Cu order for Sm compound, when the pyroelectric current is recorded only with the magnetic field both in heating and cooling cycles, i.e., the typical magnetic field cooled effect. The magnetic field cooled effect driven emergence of polarization is ferroelectric in nature, as it reverses due to the opposite poling field.

Rare earth based cobalt-ruthenium double perovskites A$_2$CoRuO$_6$ (A = La, Pr, Nd and Sm) were synthesized and investigated for their structural and magnetic properties. All the compounds crystallize in the monoclinic $P2_1/n$ structure with the indication of antisite disorder between Co and Ru sites. While, La compound is already reported to have an antiferromagnetic state below 27 K, the Pr, Nd and Sm systems are found to be ferrimagnetic below $T_c$ = 46, 55 and 78 K respectively. Field dependent magnetization data indicate prominent hysteresis loop below $T_c$ in the samples containing magnetic rare-earth ions, however magnetization does not saturate even at the highest applied fields. Our structural analysis indicates strong distortion in the Co-O-Ru bond angle, as La$^{3+}$ is replaced by smaller rare-earth ions such as Pr$^{3+}$, Nd$^{3+}$ and Sm$^{3+}$. The observed ferrimagnetism is possibly associated with the enhanced antiferromagnetic superexchange interaction in the Co-O-Ru pathway due to bond bending. The Pr, Nd and Sm samples also show small magnetocaloric effect with Nd sample showing highest value of magnitude $\sim$ 3 Jkg$^{-1}$K$^{-1}$ at 50 kOe. The change in entropy below 20 K is found to be positive in the Sm sample as compared to the negative value in the Nd counterpart., Submitted to JPCM

We report a ferroelectric order at $\ensuremath{\sim}98$ K for ${\mathrm{NiFe}}_{2}{\mathrm{O}}_{4}$, which carries an inverse spinel structure with a centrosymmetric $Fd\overline{3}m$ structure at room temperature. The value of spontaneous electric polarization is considerably high as $\ensuremath{\sim}0.29 \ensuremath{\mu}\mathrm{C}/{\mathrm{cm}}^{2}$ for 5 kV/cm poling field. The electric polarization decreases considerably ($\ensuremath{\sim}17%$) around the liquid-nitrogen temperature upon application of 50 kOe field, proposing a significant magnetoelectric coupling. The synchrotron diffraction studies confirm a structural transition at $\ensuremath{\sim}98$ K to a noncentrosymmetric structure of $P{4}_{1}22$ space group. The occurrence of polar order is associated with an ordered occupancy of Ni and Fe atoms at the octahedral sites of the $P{4}_{1}22$ structure, instead of random occupancies at the octahedral site of the inverse spinel structure. The results propose that ${\mathrm{NiFe}}_{2}{\mathrm{O}}_{4}$ is a member in the type-II multiferroics.

Mn2RuGa is known to be a ferrimagnetic compound below 460 K, while Ru2MnGa is an antiferromagnet with Neel temperature as low as 15 K. In the present work, we have studied the solid solutions of these two compositions, namely Mn 2 - x Ru 1 + x Ga (x = 0.2, 0.5), intending to design a fully compensated ferrimagnet. We successfully synthesized the compositions which crystallize with an inverse Heusler (XA) structure. The magnetic transition temperatures of both the alloys are found to be just above room temperature, and the magnetization data indicate a ferrimagnetic ordering. The compositions show spin glass like state at low temperature, which possibly emerges from the disorder and random magnetic correlations due to doping. Most interestingly, the x = 0.5 alloy shows the vanishingly small moment at low temperature, which can be explained on the basis of antiparallel alignment of moments at two inequivalent sites of Mn. The composition also shows a significant amount of exchange bias at low temperature. The observation of exchange bias for a system with a low value of net magnetization is much preferred for magneto-electric applications. Interestingly, both the samples show a transition from a high-temperature semiconducting phase to a low-temperature metallic phase. The electrical transport in the high-temperature phase is found to be dominated by small polaron hopping.

The structural and magnetic properties of disordered La2CuMnO6 double perovskite oxide are reported. Temperature variation of dc magnetization in zero field cooled and field cooled protocols manifest the cluster glass feature of the compound. The cooperative glassy magnetic state is explored by the memory effect in thermal variation as well as relaxation dynamics. The frequency dependent shift of the ac susceptibility peak satisfies dynamical scaling law with Tc ~ 26.4 K and dynamic exponent z ν ~ 3.26 proposing a cluster-glass like state. The anti-site disorder and competing exchange interactions of two different transition metal have been argued for the observed cluster glass state in this B-site disordered La2CuMnO6 double perovskite.

The compounds, NiSb2O6 (NSO) and MnSb2O6 (MSO) attract the community for the quasi one-dimensional and layered structure composed of Ni2+ and Mn2+, which orders antiferromagnetically at T N = 6.7 and 12 K, respectively. Here, we report the Griffiths-like phase much above T N in the range of 37–85 K and 25–80 K for NSO and MSO, respectively. The dc magnetization results indicate the Griffiths-like phase, following the modified Curie–Weiss law. The magneto-capacitive responses for both the compounds show anomalies at the onset of the Griffiths-like phase. Intriguingly, the low temperature synchrotron diffraction results are conclusive for determining the singularities for both the compounds. Interplay between the low-dimensionality, magnetic frustration, and magneto-elastic coupling correlates the observed short range ordered state, which is suggested as a Griffiths-like phase, above T N for both the compounds.

The magnetic behavior of cobalt pyrovanadate compound Co 2 V 2 O 7 with dichromate structure is reported. The compound undergoes long range magnetic ordering below T C =8 K and our study identifies the ground state to be a canted antiferromagnetic type with a weak ferromagnetic component. The transition at T C is found to be first-order in nature as evident from the presence of distinct thermal hysteresis in the temperature dependent magnetization data. Below T C , a significantly large value of magnetic relaxation is observed which is possibly due to the metastability associated with the first order phase transition. Interestingly, the sample exhibits a sizable magneto-caloric effect around T C (∼4.1 J kg −1 . K −1 for 50 kOe of field change) which is reasonably high among antiferromagnetic transition metal oxides with weak ferromagnetism.

Low-temperature magnetic refrigeration has attracted the attention of the cryogenics research community in the areas of technology in space science and in the liquefaction of hydrogen or other fuel gases, although it has been less researched compared to room-temperature magnetic refrigeration. Here, we report that the RVO4 (R = Gd, Ho, Er, and Yb) series is promising for low-temperature cryogenic refrigeration. GdVO4 is the most promising material, exhibiting a maximum magnetocaloric effect (ΔSmaxM) of 41.1 J kg−1 K−1 at 3 K for a change in field (ΔH) of 50 kOe. The values of ΔSmaxM are also promising, with 7.94 J kg−1 K−1 at 15 K, 19.7 J kg−1 K−1 at 2 K, and 17.4 J kg−1 K−1 at 2 K with ΔH = 50 kOe for HoVO4, ErVO4, and YbVO4, respectively. The maximum value of adiabatic temperature change (ΔTmaxad) attributed to the large magnetocaloric effect is 18 K for GdVO4 with ΔH = 50 kOe. The results further indicate that demagnetization with 50 kOe field close to the liquid hydrogen temperature at 20.3 K leads to the remarkable decrease of temperature to 3.5 K. Satisfying its potential as a refrigerant material, the thermal hysteresis of magnetization is negligible, and the values of ΔSmaxM and ΔTmaxad are as high as 12.4 J kg−1 K−1 and 8.5 K for 20 kOe change in field, which can be achieved without a superconducting magnet.

We report the dc electrical conductivity and ac impedance study of the spin chain compound CaCoRhO. The sample shows a variable range hopping-assisted dc conduction below 250 K, while a nearest neighbor small polaron hopping is observed at higher temperatures. A reasonably large frequency-independent ac dielectric permittivity (3200) is observed around room temperature. The activation energy associated with the relaxation peaks in loss tangent below 200 K is found to be close to the variable range hopping energy of the dc resistivity data which signifies the active role of the charge carrier hopping toward the ac dielectric data. The characteristic time constant associated with the relaxation (7.2 × 10−11 s) and the value of activation energy (116 meV) suggest a polaronic charge transfer in the system. The modulus analysis suggests that the relaxation in permittivity is due to the intrinsic grain effect and it is likely to be associated with charge transfer between transition metal ions in a system where their mixed valence nature is already reported. The sample also shows dielectric anomaly close to the low-temperature magnetic transition, although we failed to observe any ground state spontaneous electric polarization.

We observe ferroelectricity in an almost unexplored double perovskite La3Ni2NbO9. Ferroelectricity appears below ∼60 K, which is found to be correlated with the significant magnetostriction. A reasonably large value of spontaneous electric polarization is recorded to be ∼260 μC/m(2) at 10 K for E = 5 kV/cm, which decreases signifi- cantly upon application of a magnetic field (H), suggesting considerable magnetoelectric coupling. The dielectric permittivity is also influenced by H below the ferroelectric transition. The magnetodielectric response scales linearly to the squared magnetization, as described by the Ginzburg-Landau theory. Meticulous studies of static and dynamic features of dc magnetization and frequency dependent ac susceptibility results suggest spin-glass state below 29 K. Intrinsic magnetic memory effect is observed from zero-field cooled magnetization and isothermal remanent magnetization studies, also pointing spin-glass state below 29 K. Appearance of ferroelectricity together with a significant magnetoelectric coupling in absence of conventional long-range magnetic order is promising for searching new magnetoelectric materials.

Lithium silicate nanoglasses of composition xLi2O.(100-x)SiO2 (where x=30,40) were grown into compact of titanium dioxide nanoparticles. XPS measurements confirmed presence of Ti3+ and Ti4+ ions in the nanocomposites. The effect of TiO2 nanoparticles on lithium ion conduction was investigated in this paper. The complex conductivity spectra of lithium silicate glass nanocomposites have been measured in the frequency range of 20 Hz to 2 MHz. The temperature dependence of ionic conductivity and relaxation time obey the Vogel-Tammann-Fulcher relation. The activation energy was found to be 0.08 eV for Li+ movement in the nanoglass with x=40 due to large free volume in the nanoglass. The DC conductivity was found to be 10−5 S.cm−1 at room temperature. The formation of surface defects at the nanoglass/template interface was responsible for the lower value of activation energy. So, these nanocomposites are believed to be suitable for the fabrication of lithium-ion batteries for storage of energy.

We report transport properties of Sb2-x Sn x Te3 (x ⩽ 0.05) single crystals, where the tuning of the charge carrier densities via Sn doping significantly improves the magnetoresistance (MR) and the thermoelectric (TE) properties. The MR increases significantly at 2 K for x = 0.01, which reduces considerably with further Sn doping at x = 0.05. The MR results below 90 K for x = 0.01 satisfy the semi-classical two-band approach of Kohler's rule, which does not satisfy the MR results for x = 0.05. At 300 K, the Seebeck coefficient (S) is positive and small for x = 0.01 and it changes the sign with the further increase in Sn doping at x = 0.05 at 300 K. The value of |S| is considerable with an enhancement of the thermoelectric power factor compared to the value for x = 0.01 at 300 K. Analysis of the Hall conductivity indicates the interplay between carrier mobilities and densities, leading to the tuning of MR and TE properties with Sn doping. These results demonstrate that the p-type Sb2Te3 becomes n-type with a suitable doping engineering.

Nanodimensional glass samples of compositions xNa2O-(100–x)SiO2, with x having values of 25, 35, and 45, have been synthesized within the nanochannels of diameter ca. 5 nm of mesoporous silica SBA-15 (Santa Barbara Amorphous 15) by a sol–gel technique. The dc electrical conductivities of the nanocomposites, as well as of bulk glasses, have been determined in the temperature range 300–500 K by carrying out ac impedance measurements over the frequency range 20 Hz to 1 MHz on samples of diameter ca. 10 mm and thickness ca. 0.7 mm, and determining the intersection points of the arcs of circles in the complex impedance plots at high frequency with the real axis. The conductivities of the nanocomposites were found to be 4–5 orders of magnitude higher than those of the corresponding bulk glasses at room temperature. This may be ascribed to the presence of greater free volume in the nanoglasses as compared to their bulk counterparts, thus providing faster pathways for ion migration therein, and hence drastically lowering the activation energy of sodium ion migration. The nanocomposite with 45 mol% Na2O exhibited an electrical conductivity of the order of 10−3 S cm−1 at room temperature (ca. 300 K). The nanocomposites also showed outstanding electrochemical performances. The maximum specific capacitance was seen for the nanocomposite with nanoglass composition 45Na2O–55SiO2, amounting to 1344 F/g at a scan rate of 10 mV/s. Around 88.8% retention of capacitance over 100 successive cycles indicates good sustainability of the samples. These nanocomposites are thus highly promising for the fabrication of solid-state sodium-ion batteries.

A comparative study of the magnetic and transport properties of three Dy-In intermetallic compounds, namely DyIn3, Dy5In3 and Dy3In, is reported. DyIn3 has cubic crystal structure; on the other hand, Dy5In3 and Dy3In crystallize in tetragonal structure, albeit with different space groups. DyIn3 orders antiferromagnetically below T N = 23 K, while Dy5In3 and Dy3In show ferromagnetic-like ground state with much higher ordering temperatures (119 and 125 K respectively). The ferromagnetic compounds show significant magneto-caloric effect around their respective Curie temperatures. On the other hand, the magneto-caloric effect in DyIn3 is low but associated with the change in sign around T N . All the samples show small magneto-resistance, and it is found to be positive in case of DyIn3 at 5 K. The signature of metamagnetic transition in DyIn3 is visible in the magneto-caloric and magneto-resistance data. Efforts have been made to account the observed magnetic phenomena based on Dy concentration and Dy-Dy bond distance in these three compositions.

DyMn 2 O 5 is an intriguing multiferroic material showing multiple magnetic, electric and structural transitions. We present here the systematic study on the effect of Sr doping at the Dy site of DyMn 2 O 5 through magnetic and dielectric measurements. Doping of divalent Sr at the Dy site is expected to enhance the Mn 4 + : Mn 3 + ratio and it will also dilute the Dy site. Our study indicates large enhancement in the magnetic anomaly observed close to 43 K, which we believe to be related to the increased ferromagnetic correlations on Sr doping. Gradual increase in coercive field at 3 K with the Sr doping and decrease in bond length of adjacent Mn 4 + ions further support the enhancement of ferromagnetic correlations in the system. The parent sample shows a large magnetocaloric effect around 12 K, the magnitude of which found to decrease with increasing Sr concentration. The doping also enhances the anomaly at around 28 K observed in the dielectric permittivity versus temperature data, and this anomaly was earlier claimed to be associated with the spin reorientation as well as a simultaneous transition from one ferroelectric state to other. The electric orderings observed below 25 K are found to be susceptible to the applied magnetic field, and supports the view of Ratcliff II et al. (Phys. Rev. B 72, 060407(R) (2005)) of concomitant changes in the magnetic structure associated with the multiple electric transitions.