arXiv subjects

K. Mukherjee

Publications and source records attributed to K. Mukherjee.

At least 55 records · Page 3Linked to original sources

arXiv2019

Interplay between disorder driven Non-Fermi-liquid behavior and magnetism in Ce0.24La0.76Ge compound

In this work, we investigate the magnetic, heat capacity and electrical transport properties of Ce0.6La0.4Ge and Ce0.24La0.76Ge compounds. Our results show that two antiferromagnetic transitions (~ at 4.7 and 2.7 K) exhibited by Ce0.6La0.4Ge are suppressed below 1.8 K for Ce0.24La0.76Ge. Interestingly, for Ce0.24La0.76Ge, susceptibility, heat capacity and electrical resistivity vary with temperature as: T0.75, T0.5 and T1.6 respectively. The observation of such anomalous temperature variation suggests to the Non-Fermi-liquid (NFL) behavior due to the presence of disordered 4f spins due to Ce-site dilution. Under the application of magnetic field, it is noted that a crossover from the NFL to a magnetic state occurs around 2 Tesla, where, short-range correlations among the spins is prevalent due to the dominance of coupling between the magnetic moments via conduction electrons. Magnetoresistance scaling indicates that behavior of disorder driven NFL state is described by the dynamical mean field theory of the spin glass quantum critical point.

cond-mat.str-el↗

arXiv2019

Effect of doping of Co, Ni and Ga on magnetic and dielectric properties of layered perovskite multiferroic YBaCuFeO5

YBaCuFeO5 is one of the interesting multiferroic compounds, which exhibits magnetic ordering and dielectric anomaly above 200 K. Partial substitution of Fe with other magnetic and non-magnetic ion affects the magnetic and the structural properties of the system. We report detailed investigation of structural, magnetic and dielectric properties of YBaCuFe0.85M0.15O5 (M=Co, Ni and Ga). We observed that the partial replacement of Ni and Co in place of Fe, results in magnetic dilution and broadening of the magnetic transition and shifting towards lower temperature. The replacement of Fe with non-magnetic Ga also results in shifting of the magnetic transition to the lower temperature side. The observed dielectric relaxation behavior in these compounds is due to the charge carrier hoping. This study highlights the impacts of magnetic and non-magnetic doping at the magnetic site on magnetic and dielectric properties in layered perovskite compound YBaCuFeO5.

cond-mat.mtrl-sci↗

arXiv2019

Possibility of a new order parameter driven by multipolar moment and Fermi surface evolution in CeGe

Polycrystalline CeGe is investigated by means of DC and AC susceptibility, non-linear DC susceptibility, electrical transport and heat capacity measurements in the low temperature regime. This compound shows two peaks at low magnetic field approximately around 10.7 and 7.3 K due to antiferromagnetic ordering and subsequent spin rearrangement respectively. Investigation of non-linear DC susceptibility reveals a presence of higher order magnetization which results in the development of a new order parameter around 10.7 K. This leads to a lowering of symmetry of the magnetic state. The order parameter increases with decreasing temperature and stabilizes around 7.3 K. Consequently, the symmetry of the magnetic state is preserved below this transition. Heat capacity and resistivity results indicate the presence of a gap opening around 10.7 K on portion of Fermi surface, due to evolution of the Fermi surface. Magnetoresistance behavior and violation of Kohlers rule suggest that the evolution of Fermi surface changes the symmetry of magnetic state. The observation of new order parameter (which is of second order) is also confirmed from the Landau free energy theory.

cond-mat.str-el↗

arXiv2019

Low temperature magnetic and dielectric properties of LnBaCuFeO5 (Ln = Nd, Eu, Gd, Ho and Yb)

The layered perovskite compounds are interesting due to their intriguing physical properties. In this article we report the structural, magnetic and dielectric properties of LnBaCuFeO5 (Ln=Nd, Eu, Gd, Ho and Yb). The structural parameters decrease from Nd to Yb due to the decrease in the ionic radii of the rare earth ions. An antiferromagnetic transition is observed for EuBaCuFeO5 near 120 K along with the glassy dynamics of the electric dipoles below 100 K. The magnetic transition is absent in other compounds, which may be due to the dominance of the magnetic moment of the rare earth ions. The dielectric constant does not show any anomaly, except in the case of HoBaCuFeO5 where it shows a weak frequency dependence around 54 K. These compounds show a significant enhancement of dielectric constant at high temperatures which have been attributed to Maxwell-Wagner effect. However, no significant magneto-dielectric coupling has been observed in these layered perovskites.

cond-mat.mtrl-sci↗

arXiv2018

Observation of field induced anomalous quantum criticality in Ce0.6Y0.4NiGe2 compound

We report the results of our investigation of magnetization and heat capacity on a series of compounds Ce1-xYxNiGe2 (x = 0.1, 0.2 and 0.4) under the influence of external magnetic field. Our studies of the thermodynamic quantity -dM/dT on these compounds indicate that magnetic frustration persists in Ce0.9Y0.1NiGe2, as also reported for the parent compound CeNiGe2. The weak signature of this frustration is also noted in Ce0.8Y0.2NiGe2, whereas, it is suppressed in Ce0.6Y0.4NiGe2. Heat capacity studies on Ce0.9Y0.1NiGe2 and Ce0.8Y0.2NiGe2 indicate the presence of a new magnetic anomaly at high field which indicates that quantum criticality is absent in these compounds. However, for Ce0.6Y0.4NiGe2 such an anomaly is not noted. For this later compound, the magnetic field (H) and temperature (T) dependence of heat capacity and magnetization obey H/T scaling above critical fields. However, the obtained scaling critical parameter (δ) is 1.6, which is away from mean field value of 3. This deviation suggests the presence of unusual fluctuations and anomalous quantum criticality in these compounds. This unusual fluctuation may arise from disorderness induced by Y-substitution.

cond-mat.str-el↗

arXiv2018

Evidence of partial gap opening and Ce-site dilution effects in a heavy fermion compound CeNiGe2

We report the results of magnetization, non-linear dc susceptibility, electrical transport, and heat capacity measurements on Y-substituted heavy fermion CeNiGe2. Investigations are carried out on the compounds CeNiGe2, Ce0.9Y0.1NiGe2, Ce0.8Y0.2NiGe2 and Ce0.6Y0.4NiGe2. It is observed that with the increase in Y-concentration, the magnetic ordering temperature decreases. For CeNiGe2, below ordering temperature Arrott plots suggest the presence of spin density wave (SDW). Third and fifth order dc susceptibility indicates magnetic instability which possibly leads to partial gap opening resulting in the observation of SDW. These observations are further investigated through resistivity and heat capacity measurements which also point toward partial gap opening in CeNiGe2. Interestingly, with the increase in Y-substitution, it is noted that the gap opening is suppressed and also shifted towards lower temperature. Moreover, our investigations reveal absence of non-Fermi liquid behavior or zero field quantum critical point even after 40% dilution of Ce-site.

cond-mat.str-el↗

arXiv2018

Nature of glassy magnetic state in magnetocaloric materials Dy5Pd2-xNix (x = 0 and 1) and universal scaling analysis of R5Pd2 (R = Tb, Dy and Er)

We report a systematic investigation of the magnetic and magnetocaloric properties of Dy5Pd2 and Dy5PdNi. Our study on these compounds gave evidence that they exhibit complex magnetic behaviour along with the presence of glass-like magnetic phase. Furthermore, in these compounds both second order and first order phase transitions were present, which were validated through Arrott plots and Landau parameter analysis. AC susceptibility along with time dependent magnetisation study has confirmed the presence of double cluster glass-like freezing in both Dy5Pd2 and Dy5PdNi. These compounds show significant value of isothermal entropy change and relative cooling power and these values increased with Ni substitution. Beside conventional magnetocaloric effect, inverse magnetocaloric effect was noted in these compounds, which might arise due to the presence of complex non-equilibrium magnetic state. Along with these compounds a universal characteristic curve involving two other members of R5Pd2 family i.e. Er5Pd2 and Tb5Pd2 was constructed. The master curve reaffirmed the presence of both second and first order magnetic phase transition in such compounds which were in analogy to our results of Arrott plots and Landau parameter analysis. Additionally, magnetic entropy change followed the power law and the obtained exponent values indicated the presence of mixed magnetic interactions in these compounds.

cond-mat.mtrl-sci↗

arXiv2018

Evidence of large magnetic cooling power and double glass transition in Tb5Pd2

We report a detailed dc magnetization, ac susceptibility and magnetocaloric properties of a binary intermetallic compound Tb5Pd2. Our dc magnetization and heat capacity results reveal absence of long range ordering in this compound. Two distinct frequency dependent peaks (Tf1~60 K and Tf2~21 K) had been observed in the ac-susceptibility. Analysis of these frequency dependent peaks by Mydosh parameter, power and Vogel-Fulcher law reveals that around Tf1 the compound is at the boundary of spin glass (SG) like-cluster glass (CG) like state and it undergoes a cluster glass-like freezing below Tf2. Zero field cooled memory effect and non-linear dc susceptibility also confirmed the presence of two glassy transitions in this compound. The transformation from SG/CG boundary to CG phase was also confirmed by the magnetic relaxation measurement and Arrott plots study. Remarkably, a significant magnetic entropy change was also observed in the temperature range of 60-120 K. Additionally a large relative cooling power also observed in this compound. The observed value is comparable to those of promising refrigerant material in this temperature range and is quite notable as in this compound magnetic hysteresis was absent in this temperature range. It was noted that in this compound short-range interactions persist up to a higher temperature above Tf1 and this is responsible for the observation of significant MCE over a wide temperature range. Our studies suggest that this compound is an example of a glassy magnetic compound which shows large magnetocaloric effect.

cond-mat.mtrl-sci↗

arXiv2017

Signature of partially frustrated moments and a new magnetic phase in CeNiGe2

We report the magnetic, thermodynamic, and transport properties of a heavy fermion compound CeNiGe2. This compound undergoes two antiferromagnetic transitions around 4.1 and 3 K. It is observed in heat capacity that as magnetic field is increased to ~ 1 T, the two peak merge into a single peak around 3 K. However this peak is not suppressed under the application of magnetic field. Instead a new feature develops at 3.6 K above 1 T. The magnetic field induced new feature is investigated through entropy evolution, magnetic Gruneisen parameter and resistivity studies. These studies emphasis the fact that partial magnetic frustration due to field induced spin fluctuation is responsible for this observed feature. This partially frustrated regime develops a new antiferromagnetically ordered phase at high fields. In this compound magnetic field induced QCP is absent implying that the behavior of CeNiGe2 is not in accordance to Doniach model proposed for heavy fermions compounds.

cond-mat.str-el↗

arXiv2017

Magnetic and universal magnetocaloric behavior of rare-earth substituted DyFe0.5Cr0.5O3

We report the effect of partial substitution of Dy-site by rare-earths (R=Gd, Er and La)on the magnetic and magnetocaloric behavior of a mixed metal oxide DyFe0.5Cr0.5O3.Structural studies reveal that substitution of Dy by R has a minimal influence on the crystal structure. Magnetic and heat capacity studies show that the magnetic transition around 121 K observed for DyFe0.5Cr0.5O3 remains unchanged with rare-earth substitution, whereas the lower magnetic transition temperature is suppressed/enhanced by magnetic/non-magnetic substitution. In all these compounds, the second order nature of magnetic transition is confirmed by Arrott plots. As compared to DyFe0.5Cr0.5O3, the values of magnetic entropy change and relative cooling power are increased with magnetic rare-earth substitution while it decreases with non-magnetic rare-earth substitution. In all these compounds, magnetic entropy change follows the power law dependence of magnetic field and the value of the exponent n indicate the presence of ferromagnetic correlation in an antiferromagnetic state. A phenomenological universal master curve is also constructed for all the compounds by normalizing the entropy change with rescaled temperature using a single reference temperature. This master curve also reiterates the second order nature of the magnetic phase transition in such mixed metal oxides.

cond-mat.mtrl-sci↗

arXiv2017

Complex magnetic behaviour and evidence of superspin glass state in a binary intermetallic compound Er5Pd2

A binary intermetallic compound Er5Pd2 has been investigated using dc and ac magnetic susceptibilities, magnetic memory effect, isothermal magnetization, non-linear dc susceptibility, heat capacity and magnetocaloric effect studies. Interestingly, even though the compound does not show geometrical frustration it undergoes glassy magnetic phase transition below 17.2 K. Investigation of dc magnetisation and heat capacity data divulged absence of long-ranged magnetic ordering. Through magnetic memory effect, time dependent magnetization and ac susceptibility studies it was revealed that the compound undergoes glass-like freezing below 17.2 K. Analysis of frequency dependence of this transition temperature through scaling and Arrhenius law; along with Mydosh parameter indicate, that the dynamics in Er5Pd2 is due to the presence of strongly interacting superspins rather than individual spins. This phase transition was further investigated by non-linear dc susceptibility and was characterized by static critical exponents γ and δ. Our results indicate that this compound show signature of superspin glass at low temperature. Additionally, both conventional and inverse magnetocaloric effect was observed with large value of magnetic entropy change and relative cooling power. Our results suggest that Er5Pd2 can be classified as a superspin glass system with large magnetocaloric effect.

cond-mat.mtrl-sci↗

arXiv2017

Evolution of magnetic and dielectric properties in Sr-substituted high temperature multiferroic YBaCuFeO5

We report the evolution of structural, magnetic and dielectric properties due to partial substitution of Ba by Sr in the high temperature multiferroic YBaCuFeO5. This compound exhibits ferroelectric and antiferromagnetic transitions around 200 K and these two phenomena are presumed to be coupled with each other. Our studies on magnetic and dielectric properties of the YBa1-xSrxCuFeO5 (x = 0.0, 0.25 and 0.5) show that substitution of Sr shifts magnetic transition towards higher temperature whereas dielectric transition to lower temperature. These results points to the fact that magnetic and dielectric transitions get decoupled as a result of chemical pressure in form of Sr substitution. The nature of magnetodielectric coupling changes across the series with the presence of higher order coupling terms. Additionally in these compounds glassy dynamics of electric dipoles is observed at low temperatures.

cond-mat.mtrl-sci↗

arXiv2016

Effect of rare-earth (Er and Gd) substitution on the magnetic and multiferroic properties of DyFe0.5Cr0.5O3

We report the results of our investigations on the influence of partial substitution of Er and Gd for Dy on the magnetic and magnetoelectric properties of DyFe0.5Cr0.5O3, which is known to be a multiferroic system. Magnetic susceptibility and heat capacity data, apart from confirming the occurrence of magnetic transitions at ~ 121 and 13 K in DyFe0.5Cr0.5O3, bring out that the lower transition temperature only is suppressed by rare-earth substitution. Multiferroic behavior is found to persist in Dy0.4Ln0.6Fe0.5Cr0.5O3 (Ln= Er and Gd). There is an evidence for magnetoelectric coupling in all these materials with qualitative differences in its behavior as the temperature is changed across these two transitions. Remnant electric polarization is observed for all the compounds. The most notable observation is that electric polarization is seen to get enhanced as a result of rare-earth substitution with respect to that in DyFe0.5Cr0.5O3. Interestingly, similar trend is seen in magnetocaloric effect, consistent with the existence of magnetoelectric coupling. The results thus provide evidence for the tuning of magnetoelectric coupling by rare-earth substitution in this family of oxides.

cond-mat.str-el↗

arXiv2014

Online interpretation of numeric sign language using 2-d skeletal model

Gesturing is one of the natural modes of human communication. Signs produced by gestures can have a basic meaning coupled with additional information that is layered over the basic meaning of the sign. Sign language is an important example of communicative gestures that are highly structured and well accepted across the world as a communication medium for deaf and dumb. In this paper, an online recognition scheme is proposed to interpret the standard numeric sign language comprising of 10 basic hand symbols. A web camera is used to capture the real time hand movements as input to the system. The basic meaning of the hand gesture is extracted from the input data frame by analysing the shape of the hand, considering its orientation, movement and location to be fixed. The input hand shape is processed to identify the palm structure, fingertips and their relative positions and the presence of the extended thumb. A 2-dimensional skeletal model is generated from the acquired shape information to represent and subsequently interpret the basic meaning of the hand gesture.

cs.CV↗

arXiv2014

Online Tracking of Skin Colour Regions Against a Complex Background

Online tracking of human activity against a complex background is a challenging task for many applications. In this paper, we have developed a robust technique for localizing skin colour regions from unconstrained image frames. A simple and fast segmentation algorithm is used to train a multiplayer perceptron (MLP) for detection of skin colours. Stepper motors are synchronized with the MLP to track the movement of the skin colour regions.

cs.CV↗

arXiv2014

Anisotropic magnetodielectric coupling behavior of Ca3Co1.4Rh0.6O6 due to geometrically frustrated magnetism

We have investigated the magnetic, dielectric and magnetodielectric (MDE) behavior of a geometrically frustrated spin-chain system, Ca3Co1.4Rh0.6O6, in the single crystalline form for different orientations. The results bring out that the magnetic behavior of this compound is by itself interesting in the sense that this compound exhibits an anisotropic glassy-like magnetic behavior with a huge frequency dependence of ac susceptibility peak for an orientation along the spin-chain in the range 30-60 K; this behavior is robust to applications of large external magnetic fields (H) unlike in canonical spin-glasses. The temperature dependence of dielectric constant also shows strong frequency dependence with similar robustness to H. The isothermal H-dependent dielectric results at low temperatures establishes anisotropic MDE coupling. It is intriguing to note that there is a 'step' roughly at one-third of saturation values as in the case of isothermal magnetization curves for same temperatures (for orientation along spin-chain), a correlation hitherto unrealized for geometrically frustrated systems.

cond-mat.str-el↗

arXiv2012

Magnetic anomalies in single crystalline Tb5Si3

The polycrystalline form of the compound, Tb5Si3, crystallizing in Mn5Si3-type hexagonal structure, which was earlier believe to order antiferromagnetically below 69 K, has been recently reported by us to exhibit interesting magnetoresistance (MR) anomalies. In order to understand the magnetic anomalies of this compound better, we synthesized single crystals of this compound and subjected them to intense magnetization and MR studies. The results reveal that the magnetic behavior is strongly anisotropic as the easy axis is along a basal plane. There appear to be multiple magnetic features in the close vicinity of 70 K. In addition, there are multiple steps in isothermal magnetization (which could not be resolved in the data for polycrystalline data) for magnetic-field (H) along a basal plane. The sign of MR is positive in the magnetically ordered state, and, interestingly, the magnitude dramatically increases at the initial step for H parallel to basal plane, but decreases at subsequent steps as though the origin of these steps are different. However, for the perpendicular orientation (H || [0 0 0 1]), there is no evidence for any step either in M(H) or in MR(H). These results establish this compound is an interesting magnetic material.

cond-mat.mtrl-sci↗

arXiv2012

Observation of different spin behavior with temperature variation and Cr substitution in a multiferroic compound YMn$_2$O$_5$

In this article, the collective response of the spins is explored through low field bulk magnetic measurement for the series YMn$_{2-x}$Cr$_x$O$_5$ (x= 0.0, 0.05). Low field ac susceptibility and dc magnetization of YMn$_2$O$_5$ shows multiple transition in analogy to those observed in electrical measurement of the compound. Using various time dependent magnetization protocols it has been observed that the behavior of spins in commensurate and incommensurate phase are drastically different. YMn$_{1.95}$Cr$_{0.05}$O$_5$ undergoes a ferrimagnetic ordering with an enhanced magnetic ordering temperature as compared to the parent, which undergoes an antiferromagnetic ordering. Appearance of spontaneous magnetization without any major change in the atomic structure is rather significant since the parent compound is an important multiferroic material. In addition, magnetic memory effect is observed in the Cr substituted compound whereas it is absent in the parent compound.

cond-mat.str-el↗