arXiv subjects

B. S. Shivaram

Publications and source records attributed to B. S. Shivaram.

21 records · Page 2Linked to original sources

arXiv2014

Universality in the Magnetic Response of Metamagnetic Metals

We report in this paper, measurements of the nonlinear susceptibility χ_sub3(T) in the metamagnetic heavy fermion (HF) compound UPt3. At high temperatures, χ_sub3(T) < 0 and small. It turns positive for T less than 35K, forms a peak at T = 10K and then decreases to zero with further decreasing temperature. The peak in χ_sub3 occurs at a temperature T3 roughly half of T1, the temperature of the maximum in the linear susceptibility. We present results on URu2Si2 and UPd2Al3 to show that this feature is common to other HF materials. A two level model to describe the metamagnetic transition, with separation between the levels being the only energy scale, captures all experimentally observed features.

cond-mat.str-el↗

arXiv2011

Low Field Magnetic Susceptibility and the Hidden Order Transition in URu2Si2

Despite several decades of both experimental and theoretical work the nature of the hidden order transition at THO = 17.5 K in URu2Si2 remains enigmatic. We report here low field DC magnetization as well as AC susceptibility measurements performed on single crystals with field along the c-axis. A peak in the first order AC susceptibility is observed at T=16 K in close proximity to the well known change in slope at THO=17.5 K. Third order susceptibility measurements on the other hand reveal a signature only at 16 K with no discernible change at THO. However, both transitions are visible in the fifth order susceptibility. A signature at this lower transition, as a spontaneous ferromagnetic signal, also appears in low field DC magnetization measurements. A similar but larger ferromagnetic response appears at T~35 K. Both these ferromagnetic signatures are suppressed in a small field (B ~ 40 Gauss ||c-axis). The close proximity of the lower signature to the hidden order transition and the simultaneous presence and suppression of a ferromagnetic signature at 35 K could be due to the removal of degeneracy in the complex order-parameter of the hidden order transition due a "symmetry breaking field", at least locally within the crystals of URu2Si2.

cond-mat.str-el↗

arXiv2009

Hydrogen Absorption at Room Temperature in Nanoscale Titanium Benzene Complexes

In this letter we report the first room temperature gravimetric measurements of hydrogen absorption in nanoscale titanium-benzene complexes formed by laser ablation in a benzene atmosphere in a UHV chamber. We are able to obtain a 6% by weight absorption as predicted by recent density functional theory based calculations under the conditions of low benzene pressure (35 milli-torr) and for sub-monolayer samples. For samples synthesized under higher benzene pressures we find a systematic degradation of the hydrogen absorption.

cond-mat.mes-hall↗