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Narayanan Harish Kumar

Bio: Narayanan Harish Kumar is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topic(s): Magnetic shape-memory alloy & Paramagnetism. The author has an hindex of 1, co-authored 1 publication(s) receiving 6 citation(s).
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Abstract: We investigated the structural and magnetic properties of Cu 2 Mn 1-x Fe x Al (x = 0.25, 0.5, 0.75) alloys. Among the three compositions, only x = 0.25 composition crystallizes in single phase with L2 1 structure but its magnetic response indicates a complex magnetic structure. The magnetic isotherms were fitted to modified Langevin equation which indicates the presence of clusters with large magnetic moment. The ac susceptibility studies showed the presence of a superparamagnetic phase in the system over and above ferromagnetic order. To determine the nature of the interactions among the clusters, the variation of freezing temperature (T f ) with applied ac frequency was analyzed using different models (Neel-Arrhenius, Vogel-Fulcher, and critical slowing down model).

6 citations


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Abstract: We present a detailed study of structural, magnetic and thermodynamic properties of a series of Heusler alloys Fe2-xMnxCrAl (x=0, 0.25, 0.5, 0.75 and 1). Structural investigation of this series is carried out using high resolution synchrotron X-ray diffraction. Results suggest that with increasing Mn concentration, the L21 structure of Fe2CrAl is destabilized. The DC magnetization results show a decrement in paramagnetic (PM) to ferromagnetic (FM) phase transition temperature (TC) with increasing Mn concentration. From the systematic analysis of magnetic memory effect, heat capacity, time dependent magnetization, and DC field dependent AC susceptibility studies it is observed that, Fe2CrAl exhibits cluster glass(CG)-like transition approximately at 3.9 K (Tf2). The alloys, Fe1.75Mn0.25CrAl and Fe1.5Mn0.5CrAl exhibit double CG-like transitions near Tf1~22 K, Tf2~4.2 K and Tf1~30.4 K, Tf2~9.5 K respectively, however, in Fe1.25Mn0.75CrAl, a single CG-like transition is noted at Tf2~11.5 K below TC. Interestingly, FeMnCrAl shows the absence of long ranged magnetic ordering and this alloy undergoes three CG-like transitions at ~ 22 K (Tf*), 16.6 K (Tf1) and 11 K (Tf2). At high temperatures, a detailed analysis of temperature response of inverse DC susceptibility clearly reveals the observation of Griffiths phase (GP) above 300 K (T*) in Fe2CrAl and this phase persists with Mn concentration with a decrement in T*.

14 citations


Journal ArticleDOI
B. Venkateswarlu1, R. Hari Krishnan1, J. Arout Chelvane2, P.D. Babu3  +1 moreInstitutions (3)
Abstract: We investigated the structural stability and magnetic properties of the melt-quenched Heusler alloy-Cu2Mn0.5Fe0.5Al using X-ray diffraction (XRD), scanning electron microscopy (SEM), dc magnetization and ac susceptibility measurements respectively. The structural analysis by Rietveld refinement showed that the alloy crystallised in L21 structure with no trace of secondary phase in the XRD pattern. The dc magnetic measurements exhibited a thermal irreversibility between field-cooled (FC) and zero field cooled (ZFC) magnetization curves at an irreversible temperature Tirr. A deviation from de Almeida –Thouless like line for Tirr vs. H data was observed, suggesting a possibility of cluster glass (CG) like phase in the sample. To confirm the CG behaviour, frequency dependent ac susceptibility (χac) measurements were carried out on the sample and was analysed by Vogel-Fulcher (VF) and Critical slowing down models. We obtained large relaxation time constants (τ0) from the fit to both the phenomenological models which indicate that the origin of glassy nature may not be from randomly oriented atomic spins like in spin-glasses (SG) but of magnetic clusters. The analysis of nonlinear susceptibilities of the sample confirmed the coexistence of ferromagnetic interactions and glassy nature in the sample. Further confirmation for the glassy nature in the sample was provided by ZFC memory experiments. No anomaly was found corresponding to long-range order in the heat capacity (CP(T)) measurement and a T3/2 dependence was also seen in the electrical resistivity which indicates the magnetic glassiness in the sample.

12 citations


Journal ArticleDOI
Kavita Yadav1, K. Mukherjee1Institutions (1)
Abstract: Heusler alloy Fe2CrAl exhibits a ferromagnetic behaviour below Curie temperature (TC) ∼ 202 K along with presence of cluster glass (CG) phase near freezing temperature (Tf) ∼ 3.9 K and Griffiths phase (GP) above 300 K. The physical properties of this alloy are very sensitive to substitutions and anti-site disorder. Here, we investigate the effect of partial substitution of Mo at Cr-site on physical properties of Fe2CrAl. Structural and morphological analysis confirms the single phase cubic structure of the substituted alloys. Increment in Mo concentration shifts the TC towards lower temperature, which is ascribed to the effect of increased hybridization strength between 3d-4d states of Fe/Cr/Mo. Additionally, systematic analysis of AC susceptibility, magnetic memory effect and time dependent magnetization studies confirm the presence of CG-like phase near (Tf) ∼ 3.5 K in Fe2Cr0.95Mo0.05Al. Such feature gets suppressed towards lower temperature with an increase of Mo concentration, i.e. below 1.8 K in Fe2Cr0.85Mo0.15Al. The origin of the glassy signature is ascribed to the decrement in magnetic anisotropy with Mo concentration. A partial increment in magnetic entropy change is also noted near TC with the increase in Mo substitution. Interestingly, at high temperatures (above 350 K), GP phase persists in both the alloys due to the presence of anti-site disorder.

2 citations


Journal ArticleDOI
Yuetong Qian1, Meng Wu1, Litao Yu1, Hongwei Liu1  +6 moreInstitutions (3)
Abstract: In this work, we synthesized the Co50V34Ga16 alloy by directional solidification technique. Interestingly, the Griffiths phase was found in Co-V-Ga alloy for the first time. Using the DSC curve and the inverse DC susceptibility (χ−1) in the high temperature region, the spontaneous magnetization revealed the existence of Griffiths phase in the high temperature region. And then, according to Arrott plot, the phase transition was determined around the TC. Modified form of the Bean-Rodbell model, considering a shape memory alloy material with compressibility, spin and spin density, one defines the parameter e, which is 0.26, (e

1 citations


Journal ArticleDOI
Abstract: Structural, electronic and magnetic properties of the Heusler alloy Mn2VIn have been investigated using the density functional theory and experimental techniques. Unlike many other Heusler compounds, Mn2VIn is not predicted to be half-metallic at the optimized lattice constant, but is highly spin polarized at a slightly lower lattice constant. It however exhibits ferrimagnetic coupling between the Mn and V sublattices, as expected of Mn-based Heuslers. We have, then, synthesized the compound by arc melting and studied magnetic properties that are of interest fundamentally and for technological applications. The structural properties were determined using X-ray diffraction, revealing the presence of cubic and tetragonal phases in the sample. The chemical composition was determined using energy-dispersive X-ray spectroscopy together with the scanning electron microscope, and the magnetic properties were investigated by superconducting quantum interference device magnetometry. The alloy exhibits superparamagnetic spin blocking with a blocking temperature $T_{B}$ of 40 K.

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Author's H-index: 1

No. of papers from the Author in previous years
YearPapers
20141