arXiv subjects

Sujeet Chaudhary

Publications and source records attributed to Sujeet Chaudhary.

30 records · Page 2Linked to original sources

arXiv2017

Spin Pumping in Ion-beam Sputtered Co_{2}FeAl/Mo Bilayers:Interfacial Gilbert Damping

The spin pumping mechanism and associated interfacial Gilbert damping are demonstrated in ion-beam sputtered Co2FeAl (CFA) /Mo bilayer thin films employing ferromagnetic resonance spectroscopy. The dependence of the net spin current transportation on Mo layer thickness, 0 to 10 nm, and the enhancement of the net effective Gilbert damping are reported. The experimental data has been analyzed using spin pumping theory in terms of spin current pumped through the ferromagnet /nonmagnetic metal interface to deduce the effective spin mixing conductance and the spin-diffusion length, which are estimated to be 1.16(0.19)x10^19 m^-2 and 3.50(0.35)nm, respectively. The damping constant is found to be 8.4(0.3)x10^-3 in the Mo(3.5nm) capped CFA(8nm) sample corresponding to a ~42% enhancement of the original Gilbert damping (6.0(0.3)x10^-3) in the uncapped CFA layer. This is further confirmed by inserting a Cu dusting layer which reduces the spin transport across the CFA /Mo interface. The Mo layer thickness dependent net spin current density is found to lie in the range of 1-3 MAm^-2, which also provides additional quantitative evidence of spin pumping in this bilayer thin film system.

cond-mat.mes-hall↗

arXiv2017

Temperature-dependent Gilbert damping of Co2FeAl thin films with different degree of atomic order

Half-metallicity and low magnetic damping are perpetually sought for in spintronics materials and full Heusler alloys in this respect provide outstanding properties. However, it is challenging to obtain the well-ordered half-metallic phase in as-deposited full Heusler alloys thin films and theory has struggled to establish a fundamentals understanding of the temperature dependent Gilbert damping in these systems. Here we present a study of the temperature dependent Gilbert damping of differently ordered as-deposited Co2FeAl full Heusler alloy thin films. The sum of inter- and intraband electron scattering in conjunction with the finite electron lifetime in Bloch states govern the Gilbert damping for the well-ordered phase in contrast to the damping of partially-ordered and disordered phases which is governed by interband electronic scattering alone. These results, especially the ultralow room temperature intrinsic damping observed for the well-ordered phase provide new fundamental insights to the physical origin of the Gilbert damping in full Heusler alloy thin films.

cond-mat.mtrl-sci↗

arXiv2017

Observation of Skyrmions at Room Temperature in Co2FeAl Heusler Alloy Ultrathin Films

Magnetic skyrmions are topological spin structures having immense potential for energy efficient spintronic devices. However, observations of skyrmions at room temperature are limited to patterned nanostructures. Here, we report the observation of stable skyrmions in unpatterned Ta/Co2FeAl(CFA)/MgO thin film heterostructures at room temperature and in zero external magnetic field employing magnetic force microscopy. The skyrmions are observed in a trilayer structure comprised of heavy metal (HM)/ferromagnet (FM)/Oxide interfaces which result in strong interfacial Dzyaloshinskii-Moriya interaction (i-DMI) as evidenced by Brillouin light scattering measurements, in agreement with the results of micromagnetic simulations. We also emphasize on room temperature observation of multiple skyrmions which can be stabilized for suitable choices of CFA layer thickness, perpendicular magnetic anisotropy, and i-DMI. These results open up a new paradigm for designing room temperature spintronic devices based on skyrmions in FM continuous thin films.

cond-mat.mtrl-sci↗

arXiv2002

Thermomagnetic history effects in SmMn$_2$Ge$_2$

The intermetallic compound SmMn$_2$Ge$_2$, displaying multiple magnetic phase transitions, is being investigated in detail for its magnetization behavior near the 145 K first order ferromagnetic to antiferromagnetic transition occuring on cooling, in particular for thermomagnetic history effects in the magnetization data. The most unusual finding is that the thermomagnetic irreversibility, [= M$^{FCW}$(T)-M$^{ZFC}$(T)] at 135 K is higher in intermediate magnetic field strengths. By studying the response of the sample (i.e., thermomagnetic irreversibility and thermal hysteresis) to different histories of application of magnetic field and temperature, we demonstrate how the supercooling and superheating of the metastable magnetic phases across the first order transition at 145 K contribute to overall thermomagnetic irreversibility.

cond-mat.str-el↗

arXiv2002

Resistivity and thermoelectric power measurements on CeFe$_2$ and its pseudobinaries

Resistivity and thermoelectric power (TEP) measurements on CeFe$_2$ and two of its pseudo-binaries Ce(Fe, 5% Ir)$_2$ and Ce(Fe, 7% Ru)$_2$ between 78K and 275K are reported. The resistivity data are analysed in terms of contributions from scattering due to phonon, magnon, spin fluctuation and lattice defects, and also from interband scattering. Attempts are made to analyze the TEP data in terms of these resistivity components. Thermal hysteresis is observed in the temperature dependence of TEP in the Ir and Ru doped CeFe$_2$ samples around the ferromagnetic to antiferromagnetic transition, indicating the first order nature of this transition.

cond-mat.str-el↗

arXiv2001

First order transition from ferromagnetism to antiferromagnetism in Ce(Fe$_{0.96}$Al$_{0.04}$)$_2$: a magnetotransport study

The magnetotransport behaviour is investigated in detail across the first order magnetic phase transition from ferromagnetic to antiferromagnetic state in polycrystalline Ce(Fe$_{0.96}$Al$_{0.04}$)$_2$ sample. The study clearly brings out various generic features associated with a first order transition, viz., hysteresis, phase coexistence, supercooling and superheating, presence and limits of the metastable regimes. These results of magnetotransport study exhibit and support all the interesting thermomagnetic history effects that were observed in our earlier dc-magnetisation study on the same sample. Most notable here is the initial (or virgin) resistivity vs. field curve lying outside the hysteretic "butterfly shaped" magnetoresistivity loops obtained on cyclying the magnetic field between high enough positive and negative strengths. These findings, bearing one-to-one similarity with the data obtained in their magnetic counterpart (i.e., dc-magnetisation), have been ascribed an origin due to the arresting of this first order transition kinetics at low temperature and high magnetic field.

cond-mat.str-el↗

arXiv2001

Interesting magnetic properties of Fe$_{1-x}$Co$_x$Si alloys

Solid solution between nonmagnetic narrow gap semiconductor FeSi and diamagnetic semi-metal CoSi gives rise to interesting metallic alloys with long-range helical magnetic ordering, for a wide range of intermediate concentration. We report various interesting magnetic properties of these alloys, including low temperature re-entrant spin-glass like behaviour and a novel inverted magnetic hysteresis loop. Role of Dzyaloshinski-Moriya interaction in the magnetic response of these non-centrosymmetric alloys is discussed.

cond-mat.str-el↗

arXiv2000

Peak effect in the vortex state of V$_3$Si: a study of history dependence

We present results of transport properties measurement on a single crystal of V$_3$Si showing distinct signature of peak-effect in its vortex state. The field variation of the electrical resistance in the flux-line lattice prepared by different experimental path, namely zero field cooling (ZFC) and field cooling (FC), shows a distinct path dependence in the vicinity of the peak-effect regime. In the field cooled state, small cycling of magnetic field modifies the resistance drastically around the peak-effect regime, highlighting the metastable nature of that state in the concerned regime.

cond-mat.supr-con↗

arXiv2000

First order metamagnetic transition in CeFe$_2$ based pseudobinary alloys

We present results of dc magnetisation study showing that the low temperature antiferromagnetic state in various CeFe$_2$-based pseudobinary alloys can be transformed into ferromagnetic state through a magnetic field induced phase transition. We highlight the presence of hysteresis and phase coexistence across this metamagnetic transition and argue that the observed phase transition is of first order in nature.

cond-mat.mtrl-sci↗

arXiv2000

Peak effect in CeRu$_2$:history dependence and supercooling

We present experimental results on single crystal CeRu$_2$ showing that the extent of history dependence of peak-effect depends on the path followed in the space of field (H) and temperature (T). The (H,T) regime over which history effect is observed is larger if the vortex lattice is prepared by lowering T from above T$_C$ in constant H i.e. by field cooling. We compare this history effect with the very recently reported history dependence of peak-effect in detwinned single crystals of YBaCuO, highlighting the similarities and differences. We discuss the possibility of a first order vortex solid-solid transition in CeRu$_2$ within the realm of recent theoretical developments in the field of vortex matter.

cond-mat.supr-con↗

arXiv2000

History dependence of peak effect in CeRu$_2$ and V$_3$Si: an analogy with the random field Ising systems

We present results of transport measurements showing distinct path dependence of the electrical resistance in the superconducting vortex state of single crystal samples of CeRu$_2$ and V$_3$Si. Resistance measured in the vortex state of both the systems prepared by field cooling (FC), indicates a relatively higher degree of disorder than when it is prepared by isothermal variation of field. Small oscillations of magnetic field modify the resistance in the FC state, highlighting the metastable nature of that state. An analogy is drawn with the FC state of the random-field Ising systems.

cond-mat.supr-con↗

arXiv1998

The effect of the total density of states at Fermi level on spin polarised tunnelling in granular La0.55Ho0.15Sr0.3MnO3

We study the spin polarised tunnelling mechanism through magnetisation and magnetoresistance in the granular polycrystalline colossal magnetoresistive manganite, La0.55Ho0.15Sr0.3MnO3. This system has a ferromagnetic transition temperature (Tc) of 255 K associated with a metal-insulator transition around the same temperature. We have investigated dependence of the magnetoresistance due to spin polarised tunnelling on temperature and reduced magnetisation of the sample. We discuss the significance of our results within the realm of a model recently proposed by us to explain the spin polarised tunnelling in granular La0.7Sr0.3MnO3, in the light of the recent finding by A. Biswas et al. (cond-mat/9806084) regarding the evolution of the total density of states at Fermi level as a function of temperature in colossal magnetoresistive materials.

cond-mat.str-el↗