arXiv subjects

Sachin Gupta

Publications and source records attributed to Sachin Gupta.

31 records · Page 2Linked to original sources

arXiv2019

Monolayer MoS2 field effect transistor with low Schottky barrier height with ferromagnetic metal contacts

Two-dimensional MoS2 has emerged as promising material for nanoelectronics and spintronics due to its exotic properties. However, high contact resistance at metal semiconductor MoS2 interface still remains an open issue. Here, we report electronic properties of field effect transistor devices using monolayer MoS2 channels and permalloy (Py) as ferromagnetic (FM) metal contacts. Monolayer MoS2 channels were directly grown on SiO2/Si substrate via chemical vapor deposition technique. The increase in current with back gate voltage shows the tunability of FET characteristics. The Schottky barrier height (SBH) estimated for Py/MoS2 contacts is found to be +28.8 meV (zero-bias), which is the smallest value reported so-far for any direct metal (magnetic or non-magnetic)/monolayer MoS2 contact. With the application of gate voltage (+10 V), SBH shows a drastic reduction down to a value of -6.8 meV. The negative SBH reveals ohmic behavior of Py/MoS2 contacts. Low SBH with controlled ohmic nature of FM contacts is a primary requirement for MoS2 based spintronics and therefore using directly grown MoS2 channels in the present study can pave a path towards high performance devices for large scale applications.

physics.app-ph↗

arXiv2018

Magnetic and transport properties of Sb2Te3 doped with high concentration of Cr

We report on molecular beam epitaxy and properties of a magnetic topological insulator, Cr doped Sb2Te3. The composition analysis reveals that Cr replaces Sb site, and x-ray diffraction confirms that single phase textured crystal structure can be obtained for (CrxSb1-x)2Te3 with x up to 0.44. Further increase in x results in phase separation or precipitates in the material. The Curie temperature TC increases with x up to 0.44, and reaches to 250 K, which is the highest TC observed till now in magnetically doped topological insulators.

cond-mat.mtrl-sci↗

arXiv2017

Competing magnetic and spin gap-less semiconducting behaviour in fully compensated ferrimagnet CrVTiAl: Theory and Experiment

We report the structural, magnetic and transport properties of polycrystalline CrVTiAl alloy along with first principles calculations. It crystallizes in the LiMgPdSn type structure with lattice parameter 6.14 Å at room temperature. Absence of (111) peak along with the presence of a weak (200) peak indicates the antisite disorder of Al with Cr and V atoms. The magnetization measurements reveal a ferrimagnetic transition near 710 K and a coercive field of 100 Oe at 3 K. Very low moment and coercive field indicate fully compensated ferrimagnetism in the alloy. Temperature coefficient of resistivity is found to be negative, indicating a characteristic of semiconducting nature. Absence of exponential dependence of resistivity on temperature indicates a gapless/spin-gapless semiconducting behaviour. Electronic and magnetic properties of CrVTiAl for three possible crystallograpic configurations are studied theoretically. All the three configurations are found to be different forms of semiconductors. Ground state configuration is a fully compensated ferrimagnet with band gaps 0.58 eV and 0.30 eV for up and down spin bands respectively. The next higher energy configuration is also ferrimagnetic, but has spin-gapless semiconducting nature. The highest energy configuration corresponds to a non-magnetic gapless semiconductor. The energy differences among these configurations are quite small ($<$ 1 $\mathrm{mRy/atom}$) which hints that at finite temperatures, the alloy exists in a disordered phase, which is a mixture of the three configurations. By taking into account the theoretical and the experimental findings, we conclude that CrVTiAl is a fully compensated ferrimagnet with predominantly spin gap-less semiconductor nature.

cond-mat.mtrl-sci↗

arXiv2015

Electronic structure, magnetism and antisite disorder in CoFeCrGe and CoMnCrAl quaternary Heusler alloys

We present a combined theoretical and experimental study of two quaternary Heusler alloys CoFeCrGe (CFCG) and CoMnCrAl (CMCA), promising candidates for spintronics applications. Magnetization measurement shows the saturation magnetization and transition temperature to be $3\; μ_B$, $866$ K and $0.9 \; μ_B$, $358$ K for CFCG and CMCA respectively. The magnetization values agree fairly well with our theoretical results and also obey the Slater-Pauling rule, a prerequisite for half metallicity. A striking difference between the two systems is their structure; CFCG crystallizes in fully ordered Y-type structure while CMCA has L2$_1$ disordered structure. The antisite disorder adds a somewhat unique property to the second compound, which arises due to the probabilistic mutual exchange of Al positions with Cr/Mn and such an effect is possibly expected due to comparable electronegativities of Al and Cr/Mn. {\it Ab-initio} simulation predicted a unique transition from half metallic ferromagnet to metallic antiferromagnet beyond a critical excess amount of Al in the alloy.

cond-mat.mtrl-sci↗

arXiv2014

RRhGe (R=Tb, Dy, Er, Tm): An experimental and theoretical study

RRhGe (R=Tb, Dy, Er, Tm) compounds have been studied by a number of experimental probes and theoretical ab initio calculations. These compounds show very interesting magnetic and electrical properties. All the compounds are antiferromagnetic with some of them showing spin-reorientation transition at low temperatures. The magnetocaloric effect (MCE) estimated from magnetization data shows very good value in all these compounds. The electrical resistivity shows metallic behavior of these compounds. MR shows negative sign near ordering temperatures and positive at low temperatures. The electronic structure calculations accounting for electronic correlations in the 4f rare-earth shell reveal the closeness of the antiferromagnetic ground state and other types of magnetic orderings in the rare-earth sublattice.

cond-mat.str-el↗

arXiv2014

Experimental and theoretical investigations on magnetic and related properties of ErRuSi

We report experimental and theoretical studies of magnetic and related properties of ErRuSi compound. Various experimental techniques such as neutron diffraction, magnetization, magneto-thermal, magneto-transport, optical have been used to study the compound. Neutron diffraction shows ferromagnetic ordering at low temperatures with moments aligned in ab plane. Neutron diffraction and magnetization data show reduction in magnetic moment, which may be due to crystalline electric field effects at low temperatures. The compound shows good magnetocaloric properties with a low field adiabatic temperature change of 4.7 K, which is larger than that of many proposed materials for magnetic refrigeration at low temperatures. Magnetoresistance shows large negative value at 8 K, which changes its sign and increases in magnitude, with decrease in temperature and/or increase in field. The positive MR at low temperatures attributed to the Lorentz force effect. The electronic structure calculations accounting for electronic correlations of the 4f electrons of Er reproduces the ferromagnetic ordering and effective magnetic moment. Interband transitions between the Ru and Er d states and Er f states in one spin projection are found to form the main features of the measured optical conductivity in this compound.

cond-mat.str-el↗

arXiv2014

A comparative study of HoSn1.1Ge0.9 and DySn1.1Ge0.9 compounds using magnetic, magneto-thermal and magneto-transport measurements

Polycrystalline HoSn1.1Ge0.9 and DySn1.1Ge0.9 compounds have been studied by means of different experimental probes. Both the compounds are antiferromagnetic and show metamagnetic transition at low temperatures. HoSn1.1Ge0.9 shows a sign change in magnetocaloric effect (MCE) and magnetoresistance (MR) with field, which is attributed to the metamagnetic transition. DySn1.1Ge0.9 shows characteristics of a typical antiferromagnet, as evidenced by magnetization, MCE and MR data. 119Sn Mössbauer studies show hyperfine splitting at low temperatures, consistent with magnetization data. Thermoelectric power and resistivity measurements reveal metallic behavior in these compounds. Magnetic, magnetocaloric and the magnetoresistance data clearly show that the antiferromagnetic coupling in DySn1.1Ge0.9 is stronger than in HoSn1.1Ge0.9.

cond-mat.str-el↗

arXiv2014

Correlations among magnetic, magnetocaloric and magneto-transport properties in HoNiSi

Magnetic, magnetocaloric and magneto-transport properties of polycrystalline HoNiSi have been studied. The compound crystallizes in orthorhombic crystal structure and orders antiferromagnetically at TN=4.6 K. Magnetization isotherms show curvature at small fields, revealing a field induced metamagnetic transition. Magnetocalroic effect (MCE) has been estimated using magnetization data and is found to be 12.8 J/kg K for a field of 50 kOe. Application of field reduces the resistivity near TN, which results in a large negative MR. The maximum value of MR has been found to be -24% at 4 K for 50 kOe. Below 4 K, the compound shows positive MR with shape changing with field.

cond-mat.str-el↗

arXiv2014

Review on magnetic and related properties of RTX compounds

RTX (R=rare earths, T= 3d/4d/5d, transition metals such as Sc, Ti, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, and X=p-block elements such as Al, Ga, In, Si, Ge, Sn, As, Sb, Bi) series is a huge family of intermetallics compounds. These compounds crystallize in different crystal structures depending on the constituents. Though these compounds have been known for a long time, they came to limelight recently in view of the large magnetocaloric effect (MCE) and magnetoresistance (MR) shown by many of them. Most of these compounds crystallize in hexagonal and tetragonal crystal structures. Some of them show crystal structure modification with annealing temperature; while a few of them show iso-structural transition in the paramagnetic regime. Their magnetic ordering temperatures vary from very low temperatures to temperatures well above room temperature (~510 K). Depending on the crystal structure, they show a variety of magnetic and electrical properties. These compounds have been characterized by means of a variety of techniques/measurements such as x-ray diffraction, neutron diffraction, magnetic properties, heat capacity, magnetocaloric properties, electrical resistivity, magnetoresistance, thermoelectric power, thermal expansion, Hall effect, optical properties, XPS, Mössbauer spectroscopy, ESR, μSR, NMR, NQR etc. Some amount of work on theoretical calculations on electronic structure, crystal field interaction and exchange interactions has also been reported. The interesting aspect of this series is that they show a variety of physical properties such as Kondo effect, heavy fermion behavior, spin glass state, intermediate valence, superconductivity, multiple magnetic transitions, metamagnetism, large MCE, large positive as well as negative MR, spin orbital compensation, magnetic polaronic behavior, pseudo gap effect etc.

cond-mat.str-el↗

arXiv2014

Field induced large magnetocaloric effect and magnetoresistance in ErNiSi

Large magnetocaloric effect (MCE) and magnetoresistance (MR) together with negligible hysteresis loss has been observed in ErNiSi compound, which undergoes metamagnetic transition at low temperatures. Magnetization, heat capacity and resistivity measurements confirm the metamagnetic transition. The maximum value of isothermal entropy change and MR for a field change of 50 kOe are found to be 19.1 J/kg K and -34 %. Large MCE with negligible magnetic hysteresis loss could make this material promising for low temperature magnetic refrigeration.

cond-mat.str-el↗

arXiv2013

Observation of large positive magnetoresistance and its sign reversal in GdRhGe

Magnetic properties, heat capacity and magnetoresistance (MR) of polycrystalline GdRhGe are investigated. It shows two antiferromagnetic transitions, one at T1=31.8 K and the other at T2=24 K, and field induced metamagnetic transition over a wide temperature range. The ac susceptibility data reveal that the transition at 24 K is not simple antiferromagnetic. Dominant contributions to the heat capacity and the resistivity have been identified. MR is found to show sign reversal just below T1 and attains a large positive value of 48% at 2 K for 50 kOe. Like MR, the isothermal magnetic entropy change also undergoes a sign reversal as the temperature is varied, indicating a change of the magnetic structure and the moment amplitude in determining these properties.

cond-mat.str-el↗

arXiv2013

Observation of giant magnetocaloric effect in HoCoSi

We report the magnetic and magnetocaloric properties of HoCoSi, which shows second order ferro-para magnetic transition at 14 K. It is found to exhibit a large magnetic entropy change of 13 J/kg K for a field change of 20 kOe, which increases to 20.5 J/kg K at 50 kOe. The refrigerant capacity is found to be 135 and 410 J/kg for 20 and 50 kOe, respectively. The large, low-field adiabatic temperature change (~ 3 K) and a large refrigerant capacity make this compound a suitable candidate for magnetic refrigeration applications at around 15 K.

cond-mat.str-el↗

arXiv2013

Interplay between magnetism and magnetocaloric effect in NdCuSi

We report the magnetic, thermal, magnetocaloric and transport properties of polycrystalline NdCuSi. The compound shows a weak antiferromagnetic ordering, as confirmed by different measurements. Arrott plots indicate that the magnetic phase transition is found to be second order in nature. The isothermal magnetic entropy change calculated using the magnetization data gives a value of 11.1 J/kg K for a field change of 50 kOe. The follows h2/3 dependence (h is the reduced field) with a negative intercept, which is predicted by mean field theory for second order phase transitions. Landau theory of phase transition was applied to calculate change in entropy, which was found to be in good agreement with that calculated directly from the magnetization data. Temperature dependence of electrical resistivity shows a pronounced anomaly at the ordering temperature, which is attributed to the spin fluctuations.

cond-mat.str-el↗