arXiv subjects

V. Raghavendra Reddy

Publications and source records attributed to V. Raghavendra Reddy.

21 records · Page 2Linked to original sources

arXiv2016

Study of spin-phonon coupling and magnetic field induced spin reorientation in polycrystalline multiferroic $GdFeO_3$

The present work reports the preparation of polycrystalline multiferroic $GdFeO_3$ (GdFO) and characterization with x-ray diffraction (XRD), magnetization, temperature dependent Raman spectroscopy, temperature and magnetic field dependent $^{57}Fe$ M$\ddot{o}$ssbauer spectroscopy measurements. The sample is found to be phase pure from Rietveld refinement of XRD pattern. The M$\ddot{o}$ssbauer spectra measured in the presence of external magnetic field show the signatures of field induced spin reorientation transition, which are corroborated by magnetization measurements. From the temperature dependent variation of internal hyperfine field, N$\grave{e}$el transition temperature ($T_{N,Fe}$) of 672.5$\pm$0.2 K and critical exponent ($β$) of 0.333$\pm$0.003 is obtained. Temperature dependent (300 - 760 K) Raman spectroscopy measurements show the signatures of spin-phonon coupling and local structural re-arrangement across $T_{N,Fe}$.

cond-mat.mtrl-sci↗

arXiv2016

High resolution Kerr microscopy study of exchange bias phenomena in FePt/Fe exchange spring magnets

Magnetization and magnetic microstructure of top soft magnetic layer (Fe), which is exchange spring coupled to bottom hard magnetic layer ($L1_0$ FePt) is studied using high resolution Kerr microscopy. When the sample (FePt/Fe) is at remanent condition of hard magnetic layer, considerable shifting of Fe layer hysteresis loop from centre i.e., exchange bias phenomena is observed. It is observed that one can tune the magnitude of exchange bias shift by reaching the remanent state from different saturating fields ($H_{SAT}$) and also by varying the angle between measuring field and $H_{SAT}$. The M-H loops and domain images of top soft Fe layer demonstrates unambiguously that soft magnetic layer at remanent state in such exchange coupled system is having unidirectional anisotropy. An analogy is drawn and the observations are explained in terms of the mostly accepted models of exchange bias phenomena exhibited by bilayers consisting of ferromagnetic(FM) and anti-ferromagnetic (AFM) layers, when the AFM layer is field cooled across $N\acute{e}el$ transition temperature.

cond-mat.mtrl-sci↗

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↗