S. M. Yusuf

Bio: S. M. Yusuf is an academic researcher from Bhabha Atomic Research Centre. The author has contributed to research in topics: Magnetization & Neutron diffraction. The author has an hindex of 31, co-authored 167 publications receiving 2650 citations. Previous affiliations of S. M. Yusuf include Spanish National Research Council & Homi Bhabha National Institute.

Coexistence of sign reversal of both magnetization and exchange bias field in the core-shell type La0.2Ce0.8CrO3 nanoparticles

Abstract: We report an extraordinary coexistence of sign reversal of both magnetization and exchange bias field in the La0.2Ce0.8CrO3 nanoparticles. From the high resolution transmission electron microscopy image, and field dependence of thermoremanent and isothermoremanent magnetization measurements, the nanoparticles are found to be of core-shell nature. The core-shell configuration with an antiferromagnetic core of the Cr3+ and Ce3+ spins and a disordered shell with the uncompensated spins, explains the sign reversal of both magnetization and exchange bias field. The present study shows an excellent way of tuning the sign of both magnetization and exchange bias field in a single magnetic system.

Rounding of a first-order magnetic phase transition in Ga doped La0.67Ca0.33MnO3

Abstract: The effect of disorder on the critical properties of the ferromagnetic phase transition in colossal magnetoresistive manganite La0.67Ca0.33MnO3 has been studied by substituting Ga for Mn. It is found that, upon 10% Ga substitution, the peak in the specific heat at the Curie point T_C changes drastically and appears as a small anomaly. Static magnetization data analyzed in the asymptotic critical region using modified Arrott plots and the Kouvel-Fisher method give values for the critical exponents beta=0.387(6), gamma=1.362(2), and delta=4.60(3). The results show that the first-order transition in La0.67Ca0.33MnO3 becomes continuous by Ga substitution. The critical properties of the rounded transition in La0.67Ca0.33Mn0.9Ga0.1O3 suggest that the magnetic subsystem in this mixed-valent perovskite is close to that of a conventional isotropic ferromagnet belonging to the Heisenberg universality class with short-range interactions. It is concluded that the first-order magnetic transition in pure La0.67Ca0.33MnO3 is induced by fluctuations from a competing mode, which couples to the magnetic subsystem.

Zigzag antiferromagnetic ground state with anisotropic correlation lengths in the quasi-two-dimensional honeycomb lattice compound N a 2 C o 2 Te O 6

Abstract: The crystal structure, magnetic ground state, and the temperature-dependent microscopic spin-spin correlations of the frustrated honeycomb lattice antiferromagnet $\mathrm{N}{\mathrm{a}}_{2}\mathrm{C}{\mathrm{o}}_{2}\mathrm{Te}{\mathrm{O}}_{6}$ have been investigated by powder neutron diffraction. A long-range antiferromagnetic (AFM) ordering has been found below ${T}_{\mathrm{N}}\ensuremath{\sim}24.8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The magnetic ground state, determined to be zigzag antiferromagnetic and characterized by a propagation vector $\mathbf{k}=(1/200)$, occurs due to the competing exchange interactions up to third-nearest neighbors within the honeycomb lattice. The exceptional existence of a limited magnetic correlation length along the $c$ axis (perpendicular to the honeycomb layers in the $ab$ planes) has been found even at 1.8 K, well below the ${T}_{\mathrm{N}}\ensuremath{\sim}24.8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The observed limited correlation along the $c$ axis is explained by the disorder distribution of the Na ions within the intermediate layers between honeycomb planes. The reduced ordered moments ${m}_{\mathrm{Co}(1)}=2.77(3)\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{C}{\mathrm{o}}^{2+}$ and ${m}_{\mathrm{Co}(2)}=2.45(2)\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{C}{\mathrm{o}}^{2+}$ at 1.8 K reflect the persistence of spin fluctuations in the ordered state. Above ${T}_{\mathrm{N}}\ensuremath{\sim}24.8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the presence of short-range magnetic correlations, manifested by broad diffuse magnetic peaks in the diffraction patterns, has been found. Reverse Monte Carlo analysis of the experimental diffuse magnetic scattering data reveals that the spin correlations are mainly confined within the two-dimensional honeycomb layers ($ab$ plane) with a correlation length of $\ensuremath{\sim}12\phantom{\rule{0.16em}{0ex}}\AA{}$ at 25 K. The nature of the spin arrangements is found to be similar in both the short-range and long-range ordered magnetic states. This implies that the short-range correlation grows with decreasing temperature and leads to the zigzag AFM ordering at $T\ensuremath{\le}{T}_{\mathrm{N}}$. The present study provides a comprehensive picture of the magnetic correlations over the temperature range above and below the ${T}_{\mathrm{N}}$ and their relation to the crystal structure. The role of intermediate soft Na layers on the magnetic coupling between honeycomb planes is discussed.