arXiv subjects

V. Siruguri

Publications and source records attributed to V. Siruguri.

24 records · Page 2Linked to original sources

arXiv2013

Low temperature high magnetic field $^{57}Fe$ M$\ddot{o}$ssbauer study of kinetic arrest in $Hf_{0.77}Ta_{0.23}Fe_2$

Low temperature high magnetic field $^{57}Fe$ M$\ddot{o}$ssbauer measurements were carried out on inter-metallic $Hf_{0.77}Ta_{0.23}Fe_2$ compound by following novel paths in H-T space. The ferromagnetic (FM) fraction at 5K and zero magnetic field is shown to depend on cooling field i.e., higher the field higher is the FM fraction. M$\ddot{o}$ssbauer spectra collected in the presence of 4 Tesla magnetic field shows that the antiferromagnetic (AFM) spins cant with respect to the applied magnetic field and hence, contribute to the total bulk magnetization in this compound. The data also show induced magnetic moment even at the 2a site of AFM phase. M$\ddot{o}$ssbauer spectra collected using CHUF (cooling and heating in un-equal magnetic fields) protocol shows re-entrant transition when sample is cooled in zero field and measured during warming in 4 Tesla showing FM state as the equilibrium state. The present work is the first microscopic experimental evidence for the de-vitrification of kinetically arrested magnetic state.

cond-mat.str-el↗

arXiv2012

Neutron diffraction evidence for kinetic arrest of the first-order austenite to martensite transition in Ni37Co11Mn42.5Sn9.5

Neutron diffraction measurements, performed in presence of an external magnetic field, have been used to show structural evidence for the kinetic arrest of the first-order phase transition from the high temperature austenite phase to the low temperature martensite phase in the magnetic shape memory alloy Ni37Co11Mn42.5Sn9.5 and the formation of a glass-like arrested state (GLAS). The CHUF (cooling and heating under unequal fields) protocol has been used to establish phase coexistence of metastable and equilibrium states of GLAS in the neutron diffraction patterns. We also explore the field-temperature (H,T) phase diagram for this composition which depicts the kinetic arrest line TK(H). TK is seen to increase as H increases.

cond-mat.mtrl-sci↗

arXiv2012

Concentration dependence in kinetic arrest of first order magnetic transition in Ta doped $HfFe_2$

Magnetic behavior of the pseudo-binary alloy $Hf_{1-x}Ta_xFe_2$ has been studied, for which the zero field ferromagnetic (FM) to antiferromagnetic (AFM) transition temperature is tuned near to T=0 K. These alloys show anomalous thermomagnetic irreversibility at low temperature due to kinetic arrest of the first order AFM-FM transition. All the three studied compositions show re-entrant transition in zero field cooled warming curve and anomalous non-monotonic variation of upper critical field in isothermal magnetization. The region in H-T space, where these features of kinetic arrest manifest themselves, increases with increasing Ta concentration.

cond-mat.str-el↗

arXiv2012

Magnetic behavior of Ba_{3}Cu_{3}Sc_{4}O_{12}

The chain-like system Ba_{3}Cu_{3}Sc_4O_{12} has potentially interesting magnetic properties due to the presence of Cu^{2+} and a structure-suggested low-dimensionality. We present magnetization M versus magnetic field H and temperature T, T- and H-dependent heat-capacity C_{p}, ^{45}Sc nuclear magnetic resonance (NMR), muon spin rotation (μSR), neutron diffraction measurements and electronic structure calculations for Ba_{3}Cu_{3}Sc_{4}O_{12}. The onset of magnetic long-range antiferromagnetic order at T_{N} ~16 K is consistently evidenced from the whole gamut of our data. A significant sensitivity of T_{N} to the applied magnetic field H (T_{N}~0 K for H=70 kOe) is also reported. Coupled with a ferromagnetic Curie-Weiss temperature (θ_{CW}~65 K) in the susceptibility (from a 100 K-300 K fit), it is indicative of competing ferromagnetic and antiferromagnetic interactions. These indications are corroborated by our density functional theory based electronic structure calculations where we find the presence of significant ferromagnetic couplings between some copper ions whereas AF couplings were present between some others. Our experimental data, backed by our theoretical calculations, rule out one-dimensional magnetic behaviour suggested by the structure and the observed long-range order is due to the presence of non-negligible magnetic interactions between adjacent as well as next-nearest chains.

cond-mat.str-el↗

arXiv2011

Glass-like ordering and spatial inhomogeneity of magnetic structure in Ba3FeRu2O9 : The role of Fe/Ru-site disorder

Several doped 6H hexagonal ruthenates, having the general formula Ba3MRu2O9, have been studied over a significant period of time in order to understand the unusual magnetism of ruthenium metal. However, among them, the M=Fe compound appears different since it is observed that unlike others, the 3d Fe ions and 4d Ru ions can easily exchange their crystallographic positions and as a result many possible magnetic interactions become realizable. The present study involving several experimental methods on this compound establish that the magnetic structure of Ba3FeRu2O9 is indeed very different from all other 6H ruthenates. Local structural study reveals that the possible Fe/Ru-site disorder further extends to create local chemical inhomogeneity, affecting the high temperature magnetism of this material. There is a gradual decrease of 57Fe Mössbauer spectral intensity with decreasing temperature (below 100 K), which reveals that there is a large spread in the magnetic ordering temperatures, corresponding to many spatially inhomogeneous regions. However, finally at about 25 K, the whole compound is found to take up a global glass-like magnetic ordering.

cond-mat.mtrl-sci↗

arXiv2010

Dominance of magnetoelastic coupling in multiferroic hexagonal YMnO_3

Hexagonal YMnO_3 with space group P63cm is one of the rare examples of multiferroic materials that exhibit co-dependence of a robust ferroelectric phase along with antiferromagnetic ordering. This is primarily ascribed to tilting of the MnO_5 polyhedra driven by magnetoelectric coupling. We report on the effect of magnetic field at the atomic level in YMnO_3 by utilizing magnetic field and temperature dependent neutron diffraction measurements. We show that near the Néel temperature the lattice parameters, effective magnetic moment per site, Mn-O bond lengths and O-Mn-O bond angles show large variations and these are further modified in the presence of magnetic field. We observe distinct changes with the application of magnetic field in the paramagnetic state both in atomic positions and in the bulk dielectric constant. Our results provide unambiguous confirmation of the role played by exchange-striction over and above the much studied magnetoelectric coupling in this frustrated antiferromagnet.

cond-mat.str-el↗