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We have reported in this work the study of correlation between electrical transport and magnetic properties of La 0.5 Ca 0.5 Mn 0.98 Bi 0.02 O 3 polycrystalline sample prepared by solid state method. Structural analysis reveals that presently studied compound crystallizes in the orthorhombic structure with Pnma space group. Temperature dependence of magnetization indicates that our studied compound undergoes a paramagnetic–ferromagnetic transition at Curie temperature T C =237 K. Magnetotransport analysis was successfully carried out using percolation model in the temperature range 40–300 K for magnetic field values up to 14 T. Strong correlation between electrical and magnetic properties was observed along with the absence of charge ordering inside the structure of our sample.

CeNi2Al3 system is a potential candidate for low temperature thermoelectrics. Substitution studies, especially at the Ni site are considered to be of importance due to the drastic tuning of its physical properties. Resistivity in magnetic fields and thermoelectric power measurements of Cu doped CeNi2Al3 (x=0.0 to 0.4) system is reported in this investigation. This dense Kondo lattice system is investigated with an aim of understanding its basic transport mechanism. Negative magnetoresistance is seen for x=0.3 and 0.4 in the magnetic field up to 14 T. Deviation from the Kondo behavior occurs at temperatures close to 2 K with a down turn in resistivity. The nature of resistivity at low temperatures is investigated in view of the possible evidence for Fermi liquid behavior and also the formation of heavy Fermion in corroboration with specific heat studies. Doping dependence of linear diffusion coefficient and Sommerfeld coefficient of specific heat are analyzed and discussed in connection with the heavy Fermion formation. The results obtained show a promising trend in tuning these materials by way of Kondo route as well as by the substitution especially at the Ni site in the present system. Copyright © 2015 VBRI Press.

We have reported in this work the effect of the partial substitution of lanthanum by samarium on the structural, electrical and magnetic properties of La 0.5 Ca 0.5 MnO 3 . The magnetic study indicated that substitution promotes charge ordering and weakens ferromagnetism. Below T C =123 K, the compound La 0.4 Sm 0.1 Ca 0.5 MnO 3 is a mixture of ferromagnetic and charge ordered antiferromagnetic domains. Between T C and T CO =215 K, the structure is paramagnetic with the presence of antiferromagnetic domains. The fractions of the coexisting magnetic phases are highly dependent on the applied magnetic field value. Resistivity measurements reveal the presence of an insulating-metal transition at T ρ =123 K. The equality between T C and T ρ indicates the presence of a correlation between magnetization and resistivity. For only 1 T applied field, we have reported a colossal value of magnetoresistance reaching 73% around T C . The origin of this high value is attributed to phase separation phenomenon.

Unusual magnetoresistance observed in weak itinerant ferromagnetic metal Fe0.9Co0.1Si is addressed. We invoke localization effects significantly contributing to the positive magnetoresistance apart from quantum interference effects (QIE), a new mechanism for magnetoresistance at low temperatures. QIE are dominant only at very low temperatures while localization effects are progressive out of the sub-Kelvin domain. Dominance of localization effects in Kelvin range with increasing applied magnetic field is demonstrated. An unconventional effect of magnetic field on resistivity, favors a least dominant role of ferromagnetic correlations. The H–T phase diagram explore the regions of H3/2 (paramagnetic region) and QIE (Δσ ∝ H1/2) and its extension into the paramagnetic region. A new region of linear field dependence of MC (Δσ ∝ H) is also found and reported. Qualitative analysis of thermopower and its correspondence with electrical resistivity strengthens the concept that the same electrons are responsible for both electrical and magnetic properties. It is also reported that the onset of magnetic and QIE effects is well above TC.

The ground-state magnetic properties of hexagonal equiatomic alloy of nominal composition Mn_{0.8}Fe_{0.2}NiGe were investigated through dc magnetization and heat capacity measurements. The alloy undergoes first order martensitic transition below 140 K with simultaneous development of long range ferromagnetic ordering from the high temperature paramagnetic phase. The undoped compound MnNiGe has an antiferromagnetic ground state and it shows martensitic like structural instability well above room temperature. Fe doping at the Mn site not only brings down the martensitic transition temperature, it also induces ferromagnetism in the sample. Our study brings out two important aspects regarding the sample, namley (i) the observation of exchange bias at low temperature, and (ii) spin glass like ground state which prevails below the martensitic and magnetic transition points. In addition to the observed usual relaxation behavior the spin glass state is confirmed by zero field cooled memory experiment, thereby indicating cooperative freezing of spin and/or spin clusters rather than uncorrelated dynamics of superparamagnetic like spin clusters. We believe that doping disorder can give rise to some islands of antiferromagnetic clusters in the otherwise ferromagnetic background which can produce interfacial frustration and exchange pinning responsible for spin glass and exchange bias effect. A comparison is made with doped rare-earth manganites where similar phase separation can lead to glassy ground state., Accepted for Publication in Europhysics Letters

Electrical resistivity and heat capacity measurements on Cerium based dense Kondo compound Ce3Al have been reported. Clear signatures of first order structural transition at 108K, followed by a Kondo minimum and coherence are clearly seen in resistivity. The structural transition is robust and is not affected by magnetic fields. Heat capacity measurements reveal an anomalous enhancement in the heavy fermion character upon magnetic fields. Vollhardt invariance in specific heat C(T.H) curves have been observed at T=3.7K and at H ≈ 6T.

We study, experimentally, the zero field temperature dependence of electrical resistance and Seebeck coefficient in B20 cubic type structure Fe0.8Co0.2Si. Ferromagnetic and metal like to semiconductor like transition temperatures are determined to be 32K and 70K, respectively and electron type charge carriers contributed to the Seebeck coefficient largely and resulted in negative sign. The gradual upturn in thermopower at low temperatures is attributed to change in electronic structure due course of magnetic transition from spin unpolarized to polarized state.

Here, we explore magneto-transport properties on 3d transition monosilicide MnSi. Zero field resistance as a function of temperature for MnSi shows a drop at the onset of magnetic ordering. A strong negative magnetoresistance can be explained as the suppression of spin fluctuations and magnetic field tuning of scattering strength of conduction electrons. MnSi is useful for technological application as it shows an appreciable percentage of magnetoresistance value of 12 to 20 even at moderate fields of 2-5T, respectively.

Skutterudites is known to have fascinating ground states depending upon the void filling. Heat capacity of partially filled Pr0.8Pt4Ge12 and doubly filled Pr0.8Nd0.2Pt4Ge12 skutterudites has been investigated. Superconducting gaps have been quantified through heat capacity in the presence of magnetic fields. C/T versus T2 plot of Pr0.8Nd0.2Pt4Ge12 shows an upturn at low temperatures and this tendency increases with magnetic field, suggesting the possibility of a field induced NFL like states due to magnetic correlations co‐existing with superconductivity.

Both Ba$_4$Mn$_3$O$_{10}$ and Sr$_4$Mn$_3$O$_{10}$ crystallize in an orthorhombic crystal structure consisting of corrugated layers containing Mn$_3$O$_{12}$ polydedra. The thermal variation of magnetic susceptibility of the compositions consists of a broad hump like feature indicating the presence of low dimensional magnetic correlation. We have systematically investigated the magnetic data of these compounds and found that the experimental results match quite well with the two dimensional Heisenberg model of spin-spin interaction. The two dimensional nature of the magnetic spin-spin interaction is supported by the low temperature heat capacity data of Ba$_4$Mn$_3$O$_{10}$. Interestingly, both the samples show dielectric anomaly near the magnetic ordering temperature indicating multiferroic behavior., Comment: 7 pages, 4 figures

The resistivity and heat capacity of CeAl, a well-known Kondo system, is probed under high magnetic fields of up to 14 T. The system is known to undergo a first-order structural phase transition from hexagonal to monoclinic phase at 110 K. The current study has revealed that this structural transition is a robust one under high magnetic fields. However, clear dispersion in resistivity and heat capacity are seen in the presence of high magnetic fields below 30 K, whose analysis suggest its nearness to quantum critical point (QCP). Systematic vanishing of Kondo ordering ( behaviour) and the appearance of non-Fermi liquid behaviour (+ behaviour) around 6–9 T region at low temperatures suggest that the system settles for a QCP. In line with the resistivity, the heat capacity also revealed signatures reminiscent of a non-Fermi liquid. The first-time confirmation about the existence of a QCP in stoichiometric CeAl makes this already-known compound more interesting because it could lead to the discovery of possible new ground states.

The calorimetric and thermopower measurements on Dy5Ge2Si2 are presented. The antiferromagnetic ordering resulted in a sharp peak in specific heat and paramagnetic temperature as a shoulder. Magnetic entropy (Smag) is estimated from the magnetic heat capacity, Cmag and is in good agreement with the theoretically calculated value. A small note on correct assessment of Smag is presented. Thermoelectric power is analysed in line with the specific heat and a temperature region of magnetic correlations is identified. Charge carrier density n~2.5x1023 cm−3 is calculated using Sommerfeld parameter γ and diffusion thermopower constant σD.

We have investigated the partially filled Skutterudite Pr0.5Pt4Ge12 for its superconducting properties. Resistivity measurements of Pr0.5Pt4Ge12 down to 2K and in the presence of fields up to 2T are reported. The superconducting transition, Tc of ~7.66K observed from zero fields of Resistivity and Heat Capacity measurements. The interesting observation is that the superconductivity survives even at a 50% filling of Pr in the parent compound and its Tc is equal to that of fully doped PrPt4Ge12. We have estimated relevant parameters of interest like the electron phonon coupling constant, critical field, energy gap ratio, coherence length etc.

Mn11Ge8 undergoes long range ferromagnetic ordering at 274 K followed by non-collinear antiferromagnetic structure below 150 K. Our investigations indicate the existence of large positive magnetoresistance which changes sign depending upon the applied field and temperature. In the temperature variation of resistivity and heat capacity, the sample shows very large coefficients of quadratic and linear terms, respectively. This indicates the existence of giant spin fluctuation despite the fact that the sample is in a magnetically ordered state. The Mn-moments possibly have both localized and itinerant character and the anomaly appears to be associated with the local moment spin fluctuations mediated via itinerant electrons. The large positive magnetoresistance is believed to be originated from the possible development of short range antiferromagnetic clusters on application of magnetic field.

The theoretically proposed pseudogap semimetal CoSi has been investigated by detailed experimental studies of magnetotransport, calorimetric and thermopower measurements. The two parallel resistor model is applied to understand its semimetal nature. The obtained gap is around 13 meV. The conduction process is explained by the single relaxation method by implementing Kohler's rule, , . The excess heat capacity is a consequence of thermally activated behaviour across the gap and the calculated is about . At K, the metallic behaviour without the gap, vanishing of excess heat capacity, reasonable metallic value of and linear diffusion thermopower, signifies the closure of pseudogap. The correlation amongst the T-dependent features of resistivity, excess heat capacity and thermoelectric power reveals the hidden metal-to-insulator transition in CoSi. The high magnetoresistance at low temperatures is reported to arise due to Lorentz force and its applications as a low temperature magnetic field sensor is also discussed.

We investigated the effect of magnetic (Mn) and nonmagnetic (Ga) doping at the Cr site of the layered geometrically frustrated antiferromagnetic compound LiCrO2. 10% Ga doping at the Cr site does not invoke any metastability typical of a glassy magnetic state. However, similar amount of Mn doping drives the system to a spin glass (SG) state which is particularly evident from the magnetic memory and heat capacity studies. The onset of glassy state in 10% Mn doped sample is of reentrant type developing out of higher temperature antiferromagnetic state. The SG state in the Mn-doped sample shows a true reentry with the complete disappearance of the antiferromagnetic phase below the SG transition. The lack of SG state on Ga doping indicates the importance of random ferromagnetic/antiferromagnetic bonds for the glassy ground state in LiCrO2.