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P. Chaddah

Publications and source records attributed to P. Chaddah.

64 records · Page 4Linked to original sources
arXiv2000

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

Results of dc magnetization study are presented showing interesting thermomagnetic history effects across the antiferromagnetic to ferromagnetic transition in Ce(Fe$_{0.96}$Al$_{0.04})_2$. Specifically, we observe (i)ZFC/FC irreversibility rising with increasing field; (ii) virgin curve lying outside the envelope M-H curve. We argue that these effects are quite different from the characteristics seen in spin-glasses or in hard ferromagnets; they can be understood as metastabilities associated with a first order magnetic phase transition.

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

Calculation of minor hysteresis loops under metastable to stable transformations in vortex matter

We present a model in which metastable supercooled phase and stable equilibrium phase of vortex matter coexist in different regions of a sample. Minor hysteresis loops are calculated with the simple assumption of the two phases of vortex matter having field-independent critical current densities. We use our earlier published ideas that the free energy barrier separating the metastable and stable phases reduces as the magnetic induction moves farther from the first order phase transition line, and that metastable to stable transformations occur in local regions of the sample when the local energy dissipation exceeds a critical value. Previously reported anomalous features in minor hysteresis loops are reproduced, and calculated field profiles are presented.

cond-mat.supr-con↗
arXiv2000

Vortex Matter and its Phase Transitions

The mixed state of type II superconductors has magnetic flux penetrating the sample in the form of vortices, with each vortex carrying an identical quantum of flux. These vortices generally form a triangular lattice under weak mutually repulsive forces; the lattice spacing can be easily varied over many orders of magnitude by varying the external magnetic field. The elastic moduli of this lattice are small and this soft vortex matter can undergo phase transitions like normal matter, but with thermal fluctuations and underlying defects playing an important role. We discuss experimental studies on vortex matter phase transitions, with some emphasis on DC magnetisation measurements investigating the nature of the phase transition.

cond-mat.supr-con↗
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↗
arXiv1999

Metastabilities in vortex matter

We extend the classical theory for supercooling across first order phase transitions to the case when both density and temperature are control variables. The observable region of metastability then depends on the path followed in this space of two variables. Since the density of vortex matter in superconductors can be easily varied over a wide range by varying applied field, it is ideal for experimental tests. We found, in our studies on the `peak effect' in the mixed state of superconducting CeRu$_2$, supercooled states whose observable region of metastability depends on the path followed in (H,T) space, consistent with our predictions. We also discuss phenomena in hard superconductors that are well understood within Bean's critical state model. We conclude that the path dependence of metastablity associated with hindered kinetics may be opposite to that predicted for metastability associated with supercooling across a first order transition.

cond-mat.supr-con↗
arXiv1999

Supercooling across first-order phase transitions in vortex matter

Hysteresis in cycling through first-order phase transitions in vortex matter, akin to the well-studied phenomenon of supercooling of water, has been discussed in literature. Hysteresis can be seen while varying either temperature T or magnetic field H (and thus the density of vortices). Our recent work on phase transitions with two control variables shows that the observable region of metastability of the supercooled phase would depend on the path followed in H-T space, and will be larger when T is lowered at constant H compared to the case when H is lowered at constant T. We discuss the effect of isothermal field variations on metastable supercooled states produced by field-cooling. This path dependence is not a priori applicable to metastability caused by reduced diffusivity or hindered kinetics.

cond-mat.supr-con↗