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In the new van der Waals Kondo-lattice Fe$_3$GeTe$_2$, itinerant ferromagnetism and heavy fermionic behaviour coexist. Both the key properties of such a system namely a spin-polarized Fermi surface and a low Fermi momentum are expected to significantly alter Andreev reflection dominated transport at a contact with a superconducting electrode, and display unconventional proximity-induced superconductivity. We observed interplay between Andreev reflection and Kondo resonance at mesoscopic interfaces between superconducting Nb and Fe$_3$GeTe$_2$. Above the critical temperature ($T_c$) of Nb, the recorded differential conductance ($dI/dV$) spectra display a robust zero-bias anomaly which is described well by a characteristic Fano line shape arising from Kondo resonance. Below $T_c$, the Fano line mixes with Andreev reflection dominated $dI/dV$ leading to a dramatic, unconventional suppression of conductance at zero bias. As a consequence, an analysis of the Andreev reflection spectra within a spin-polarized model yields an anomalously large spin-polarization which is not explained by the density of states of the spin-split bands at the Fermi surface alone. The results open up the possibilities of fascinating interplay between various quantum phenomena that may potentially emerge at the mesoscopic superconducting interfaces involving Kondo lattice systems hosting spin-polarized conduction electrons., To appear in Physical Review B

The discovery of fascinating ways to control and manipulate antiferromagnetic materials have garnered considerable attention as an attractive platform to explore novel spintronic phenomena and functionalities. Layered antiferromagnets (AFMs) exhibiting interesting magnetic structures, can serve as an attractive starting point to establish novel functionalities down to the two-dimensional limit. In this work, we explore the magnetoresistive properties of the spin-ladder AFM TaFe$_{1.25}$Te$_3$. Magnetization studies reveal an anisotropic magnetic behavior resulting in the stabilization of a spin-flop configuration for H $\perp$ (10-1) plane (i.e., out-of-plane direction). Angle-dependent longitudinal and transverse magnetoresistances show an unusual anharmonic behavior. A significant anisotropic enhancement of magnetoresistance when H $\perp$ (10-1) plane compared to H $\parallel$ (10-1) directions has been observed. The present results deepen our understanding of the magnetoresistive properties of low-dimensional layered AFMs, and point towards the possibility of utilizing these novel material systems for antiferromagnetic spintronics., Comment: 7 pages, 7 figures

We have performed 59Co zero field nuclear magnetic resonance (NMR) experiment at 4 K on Co x Cu 1 - x (x = 0.10, 0.32 and 0.76) nanogranular alloys. The NMR signal arises from Co rich ferromagnetic clusters formed within the Cu matrix. The analysis of NMR spectra shows that the resonance peaks arise from both fcc and hcp phases of Co. However, Co nuclei experience magnetic hyperfine field from Co only environment as well as other environments in which nearest-neighbor (NN) Co atoms are replaced by Cu. Assuming that these two environments constitute the core and the shell of the Co clusters, it is estimated using previous magnetization measurements that the contribution of core dominates in the ferromagnetism of the particles though it occupies only about 20% of the volume of Co clusters even for high Co containing alloys.

Superconducting crystals with a lack of inversion symmetry can potentially host unconventional pairing. However, till today, no direct conclusive experimental evidence of such unconventional order parameters in non-centrosymmetric superconductors has been reported. In this paper, through direct measurement of the superconducting energy gap by scanning tunnelling spectroscopy, we report the existence of both s-wave (singlet) and p-wave (triplet) pairing symmetries in non-centrosymmetric Ru$$_7$$ 7 B$$_3$$ 3 . Our temperature and magnetic field-dependent studies also indicate that the relative amplitudes of the singlet and triplet components change differently with temperature.

Two-dimensional (2D) van der Waals (vdW) magnetic materials have attracted a lot of attention owing to the stabilization of long-range magnetic order down to atomic dimensions, and the prospect of novel spintronic devices with unique functionalities. The clarification of the magnetoresistive properties and its correlation to the underlying magnetic configurations is essential for 2D vdW-based spintronic devices. Here, the effect of Co-doping on the magnetic and magnetotransport properties of Fe3GeTe2 have been investigated. Magnetotransport measurements reveal an unusual Hall effect behavior whose strength was considerably modified by Co-doping and attributed to arise from the underlying complicated spin textures. The present results provide a clue to tailoring of the underlying interactions necessary for the realization of a variety of unconventional spin textures for 2D vdW FM-based spintronics., Comment: 20 pages, 6 figures

The present study involves investigaton of magnetocaloric effect of Pr0.67Ca0.33MnO3-La0.67Sr0.33MnO3 nanocomposite materials above room temperature. From application point of view in magnetic refrigeration our study highlights the enhancement of operating temperature region compared to the well known La0.67Sr0.33MnO3 refrigerant material above room temperature. Comparison has also been made with the magnetocaloric properties of La0.67Sr0.33MnO3 nanomaterials. The modification of the magnetocaloric entropy changes (broadening of the temperature dependent magnetic entropy change) is addressed due to the effect of the gradual melting of antiferromagnetic charge ordered state of the Pr0.67Ca0.33MnO3 nanoparticles in such nanocomposite materials.

We report a large enhancement of magnetocaloric entropy change in vanadium substituted intermetallic compounds Nd ( Co 1 − x V x ) 2 Si 2 (x = 0.20 and 0.35). The antiferromagnetic parent compound NdCo2Si2 exhibits inverse magnetocaloric response. Upon vanadium doping, antiferromagnetic transition is gradually suppressed and there is a drastic modification of the ground state, with appearance of ferromagnetism in Nd ( Co 0.65 V 0.35 ) 2 Si 2 . Such modifications are reflected in the magnetocaloric properties of the parent and the doped compounds. In comparison to the inverse magnetocaloric response of the parent compound, the doped compound with x = 0.35 shows a conventional magnetocaloric effect that is large in magnitude compared to the parent compound. A table-like MCE in a wide-temperature range of 5–60 K have been observed in Nd ( Co 0.65 V 0.35 ) 2 Si 2 . The present study demonstrates enhancement of magnetic entropy by way of substitution at the transition metal site in these compounds.

The type II Dirac semimetal PdTe[Formula: see text] is unique in the family of topological parent materials because it displays a superconducting ground state below 1.7 K. Despite wide speculation on the possibility of an unconventional topological superconducting phase, tunneling and heat capacity measurements revealed that the superconducting phase of PdTe[Formula: see text] follows predictions of the microscopic theory of Bardeen, Cooper and Schrieffer for conventional superconductors. The superconducting phase in PdTe[Formula: see text] is further interesting because it also displays properties that are characteristic of type-I superconductors and are generally unexpected for binary compounds. Here, from scanning tunneling spectroscopic measurements we show that the surface of PdTe[Formula: see text] displays intrinsic electronic inhomogeneities in the normal state which leads to a mixed type I and type II superconducting behaviour along with a spatial distribution of critical fields in the superconducting state. Understanding of the origin of such inhomogeneities may be important for understanding the topological properties of PdTe[Formula: see text] in the normal state.

In intermetallic compounds RECo2Si2 (RE=Pr and Nd), cobalt has been partially substituted by vanadium to obtain RE(Co1−xVx)2Si2 ( 0 ≤ x ≤ 0.35 ). The parent compounds are antiferromagnetic below about 30 K due to the ordering of localized magnetic moments that are present only on rare-earth ions, cobalt being non-magnetic in the parent compounds. The present study demonstrates that in these compounds where 3 d and 4 f ions occupy different layers in the crystal structure, V substitution and subsequent lattice expansion results in the occurrence of inequivalent magnetic ions and complex interactions that lead to multiple magnetic transitions. At temperatures around 40–50 K, the temperature dependence of magnetization indicates a ferrimagnetic transition which is accompanied by a rapid decrease in the temperature dependence of resistivity. Below temperatures ∼30 K, the samples begin to show ferromagnetic-like behavior with the appearance of a coercive field and saturation in the magnetization at magnetic fields above ∼2 T. These two magnetic transitions are indicated also by prominent λ-like peaks in specific heat measurements. At around 10 K, a sharp drop in the resistivity indicates another magnetic transition which is followed by a rapid increase in coercive field with decrease in temperature. In a magnetic field of 9 T, the latter transition shifts to a lower temperature and that leads to a positive magnetoresistance. The onset of ferromagnetism at ∼30 K is accompanied with an exchange bias field which is observed for the first time in layered intermetallic compounds. The exchange bias field increases rapidly below the transition at ∼10 K and reaches ∼16% of coercive field at 2 K.

The magnetoresistance (MR) and magnetocaloric properties of naturally occurring layered compound NdRu2Si2 with a Neel temperature TN = 24 K have been investigated in the temperature range 60 ≥ T ≥ 1.8 K. It has been shown that a high external magnetic field greatly modifies the MR properties of the compound which in its low temperature ferromagnetic state (T

The surface states of topological insulators (TI) are protected by time reversal symmetry and they display intrinsic spin helicity where the momentum of the charge carriers decides their spin states. As a consequence, a current injected through the surface states becomes spin polarized and this transport spin-polarization leads to a proportionate suppression of Andreev reflection in superconductor/TI junctions. Here we show that upon doping Bi

The type II Dirac semimetal PdTe$_2$ is unique in the family of topological parent materials because it displays a superconducting ground state below 1.7 K. Despite wide speculations on the possibility of an unconventional topological superconducting phase, tunneling and heat capacity measurements revealed that the superconducting phase of PdTe$_2$ follows predictions of the microscopic theory of Bardeen, Cooper and Shriefer (BCS) for conventional superconductors. The superconducting phase in PdTe$_2$ is further interesting because it also displays properties that are characteristics of type-I superconductors and are generally unexpected for binary compounds. Here, from scanning tunneling spectroscopic measurements we show that the surface of PdTe$_2$ displays intrinsic electronic inhomegenities in the normal state which leads to a mixed type I and type II superconducting behaviour along with a spatial distribution of critical fields in the superconducting state. Understanding of the origin of such inhomogeneities may be important for understanding the topological properties of PdTe$_2$ in the normal state., 3 Figures

The magnetic, magneto-transport and magnetocaloric properties of antiferromagnetic intermetallic compound NdCo2Si2 (T-N = 32 K) have been studied. The compound yields a positive magnetoresistance (MR) of about similar to 123% at similar to 5 K in 8 T magnetic field. The MR value is significantly large vis - a - vis earlier reports of large MR in intermetallic compounds, and possibly associated with the changes in magnetic structure of the compound. The large MR value can be explained in terms of field induced pseudo-gaps on Fermi surface. (C) 2017 Elsevier B.V. All rights reserved.

The surface states of topological insulators (TI) are protected by time reversal symmetry and they display intrinsic spin helicity where the momentum of the charge carriers decides their spin states. As a consequence, a current injected through the surface states becomes spin polarized and this transport spin-polarization leads to a proportionate suppression of Andreev reflection in superconductor/TI junctions. Here we show that upon doping Bi2Se3 with Mn, the transport spin-polarization is seen to be monotonically suppressed. The parent compound Bi2Se3 is found to exhibit a transport spin-polarization of about 63% whereas crystals with 10% Mn doping show transport spin-polarization of about 48%. This suppression is accompanied by an increasing ferromagnetic order of the crystals with Mn doping. Scanning tunneling spectroscopy shows that the topological protection of the surface states reduce due to Mn doping. The net measured transport spin-polarization is due to a competition of this effect with the increased magnetization on Mn doping. The present results provide important insights for the choice of magnetic topological insulators for spintronic applications., Comment: Accepted in Journal of Physics: Condensed Matter, 5 PAGES, 5 FIGURES

Nanostructured CoCu granular alloys have been prepared by borohydride reduction of CuCl2 and CoCl2 salt solutions using cetyltrimethylammonium bromide (CTAB) as a surfactant. Characterization by inductively coupled plasma optical emission spectroscopy (ICPOES), X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies yields spherical particles of CoxCu1−x ( x ∼ 0.01 – 0.3 ) of average size 8–25 nm formed in a face-centered-cubic (fcc) lattice as in copper. Studies of zero-field-cooled/field-cooled (ZFC/FC) magnetization and thermoremanent magnetization (TRM) have been performed in the temperature range 4–300 K, and the results have been analyzed by independent particle model. At the lowest cobalt concentration ( x ∼ 0.01 ), the alloy is superparamagnetic and there is no blocking of magnetization down to 4 K. For all other samples, the magnetization at low magnetic field is characterized by a blocking temperature distribution which is not influenced by the Co content in samples. Study of hysteresis loops shows that the magnetization at any temperature 4–300 K is a sum of ferromagnetic (FM), superparamagnetic (SPM) and paramagnetic (PM) contributions. The FM part increases and SPM part decreases with increase in Co content. However, the values of coercivity and magnetic anisotropy constant do not depend on Co content. The results suggest that CoxCu1−x alloys are formed in a spherical core-shell type structure with cobalt being concentrated near the core of particles.

Magnetic studies have been performed to characterize Co0.3Cu0.7 granular alloy synthesized by chemical reduction. The alloy consists of superparamagnetic (SPM) particles with a mean size of 14 nm and a blocking temperature distribution extending to ∼380 K. Even at 4 K where the alloy is largely ferromagnetic, the average magnetic moment of cobalt is smaller than its expected value indicating that not all Co atoms contribute to ferromagnetism. A significant temperature dependent exchange bias field is obtained from above 100 K down to 2 K. These observations suggest that the particles have a Co rich SPM core, surrounded by uncompensated dilute Co spin moments at the surface. Such a distribution, with lowering of temperature, leads to the co-existence of ferromagnetic (FM) and antiferromagnetic (AFM) interactions in the core and surface regions, respectively. Also, the sample exhibits a weak spin-glass like ordering occurring at ∼7 K. The overall behavior of the system is that of an assembly of almost non-interacting magnetic nanoparticles as suggested by the study of relaxation of magnetization. If during relaxation certain external conditions are temporarily disturbed, e.g., by lowering the temperature or changing the magnetic field the magnetization also changes accordingly; but as the conditions are restored the magnetization returns to its previous value. Such magnetic ‘memory effect’ has been studied with various experimental protocols and persists strongly even at room temperature.

The physical systems with ferromagnetism and 'bad' metallicity hosting unusual transport properties are playgrounds of novel quantum phenomena. Recently EuTi1-x Nb x O3 emerged as a ferromagnetic system where non-trivial temperature dependent transport properties are observed due to coexistence and competition of various magnetic and non-magnetic scattering processes. In the ferromagnetic state, the resistivity shows a T 2 temperature dependence possibly due to electron-magnon scattering and above the Curie temperature [Formula: see text], the dependence changes to T 3/2 behaviour indicating a correlation between transport and magnetic properties. In this paper, we show that the transport spin-polarization ([Formula: see text]) in EuTi1-x Nb x O3, a low Curie temperature ferromagnet, is as high (∼40%) as that in some of the metallic ferromagnets with high Curie temperatures. In addition, owing to the low Curie temperature of EuTi1-x Nb x O3, the temperature (T) dependence of [Formula: see text] could be measured systematically up to [Formula: see text] which revealed a proportionate relationship with magnetization [Formula: see text] versus T. This indicates that such proportionality is far more universally valid than the ferromagnets with ideal parabolic bands. Furthermore, our band structure calculations not only helped to understand the origin of such high spin polarization in EuTi1-x Nb x O3 but also provided a route to estimate the Hubbard U parameter in complex metallic ferromagnets in general using experimental inputs.

Electrical resistivity of nanostructured granular alloys ${\mathrm{Co}}_{x}{\mathrm{Cu}}_{1\ensuremath{-}x}$ ($x\ensuremath{\sim}0.01$--$0.76$) prepared by the chemical reduction method is investigated in the temperature range 2--300 K. The samples with a low cobalt content of $x\ensuremath{\le}0.1$ show a metallic resistivity behavior. For samples with a higher cobalt content, $x\ensuremath{\ge}0.17$, the resistivity shows a minimum. The minimum becomes more pronounced as Co content ($x$) increases and also as the temperature of minimum resistivity, ${T}_{\text{min}}$, increases with $x$. The resistivity minimum is obtained in this magnetic alloy system even for a cobalt concentration as high as $\ensuremath{\sim}76%$. Application of an external magnetic field has a negligible effect on the resistivity behavior. Detailed analysis suggests that the low-temperature upturn in resistivity most probably arises due to elastic electron-electron interaction (the quantum-interference effect). Magnetic measurements at 4 K on the same samples show the absence of long-range magnetic interaction and evidence of increasing magnetic disorder as $x$ increases beyond $\ensuremath{\sim}10%$. Combining the results of the two types of measurements, a model of formation of these alloy particles involving random clusters of Co atoms within the Cu matrix has been proposed.

Nanostructured CoCu granular alloys CoxCu1-x (x ≤ 0.3) have been prepared by chemical reduction method using NaBH4 as a reducing agent. Electronic transport properties are studied in the temperature range 4-300 K. Resistance exhibits a metallic behavior below room temperature and draws a minimum near 20 K in all the samples except in Co0.3Cu0.7. This low temperature resistivity minimum diminishes with applied magnetic field. There is also a logarithmic temperature dependence of resistivity at temperatures below 20 K. This phenomenon indicates a Kondo-like scattering mechanism involving magnetic Co impurity spin clusters in Cu host.

In PrCo2Si2 and NdCo2Si2, Co has been partially substituted by V. Vanadium having a larger atomic radius than cobalt, the substitution results in a negative pressure affecting the magnetic properties of the compound. The samples RE(Co1-xVx)2Si2 (RE = Pr, Nd; x = 0, 0.20, 0.35) were prepared by melting the corresponding elements in arc furnace and characterized using x-ray diffraction. Magnetometric measurements show that the parent compounds PrCo2Si2 and NdCo2Si2 are antiferromagnetic, as reported. With doping, ferrimagnetic behaviour is observed from temperature dependence of inverse susceptibility at about 50 K. At lower than 30 K, the magnetizations tend to saturate at high fields. From the field dependence of magnetization, the hysteresis loops and also coercive fields as observed, the samples exhibit ferromagnetism below ∼ 30 K. Exchange bias effect is also observed in the high V containing sample. The specific heat studies of the samples show transitions consistent with the magnetization data. Pr(Co...