Engineering topics
Dahal, A.
Publications and source records attributed to Dahal, A..
Perovskite magnet with quantum mechanical glassiness
Magnetic materials of strongly correlated origin are at the forefront of research in the exploration of new quantum mechanical properties involving spin and charges. Quantum magnetic material with certain intrinsic functionalities, such as continuously fluctuating spins to the lowest accessible temperature - reminiscing a liquid pattern, is argued to form a new phase of matter. Envisaging a phenomenon where the continuously fluctuating spins are also randomly frozen in space, can diminish the distinction between the two opposite extremes of quantum and classical magnetism. Here, we report new evidence in this regard where the coexistence of quantum spin continuum with a spin glass order in Co-doped CaRuO3 perovskite is demonstrated. In experimental investigations of Co-doped CaRuO3 perovskite, we find that (a) a continuum spectrum in the energy-momentum space, due to the uncorrelated spin fluctuations, persists across the weak spin glass transition at T G ≃ 23 K and (b) the quantum fluctuation of magnetic moment is spatially confined to individual sites only, thereby making it an extremely local event. Thus, the fluctuating spins, at a given time, are also randomly frozen macroscopically. The experimental observations suggest the discovery of a new magnetic phase at the cross-road of classical and quantum physics in strongly correlated perovskite materials.
Spin correlation in trigonal EuMn 2 As 2
The trigonal structure of EuMn 2 As 2 is an anomaly in the tetragonal 122-type pnictide family. Here, we report a detailed investigation of the underlying magnetic correlations in single crystal EuMn 2 As 2 using high-resolution elastic neutron-scattering measurements. The system undergoes two successive antiferromagnetic transitions at T = 135 K and 14.4 K, respectively. Numerical modeling of the experimental data reveals the long-range antiferromagnetic correlation of Mn-ions in the a - b plane below T N 1 = 135 K . Mn spins are aligned closer to the diagonal axis of the unit cell. The lower temperature transition, below T N 2 = 14.4 K , is discovered to arise due to the long-range antiferromagnetic correlation of Eu spins that are rotated by θ = 55 ° from the c axis of the unit cell.
Scaling of nonlinear susceptibilities in an artificial permalloy honeycomb lattice
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Fractional electrical dimensionality in the spin solid phase of artificial honeycomb lattice
Two-dimensional artificial magnetic honeycomb lattices are at the forefront of research on unconventional magnetic materials. Among the many emergent magnetic phases that are predicted to arise as a function of temperature, the low temperature spin solid phase with zero magnetization and entropy is of special importance. Here, we report an interesting perspective to the consequence of spin solid order in an artificial honeycomb lattice of ultra-small connected elements using electrical dimensionality analysis. At low temperature, T ≤ 30 K, the system exhibits a very strong insulating characteristic. The electrical dimensionality analysis of the experimental data reveals a fractional dimensionality of d = 0.6(0.04) in the spin solid phase of honeycomb lattice at low temperature. The much smaller electrical dimension in the spin solid phase, perhaps, underscores the strong insulating behavior in this system. Furthermore, the fractional dimensionality in an otherwise two-dimensional system suggests a non-surface-like electrical transport at low temperature in an artificial honeycomb lattice.
Temperature-dependent magnetism in artificial honeycomb lattice of connected elements
Artificial magnetic honeycomb lattices are expected to exhibit a broad and tunable range of novel magnetic phenomena that would be difficult to achieve in natural materials, such as long-range spin ice, entropy-driven magnetic charge-ordered states, and spin order due to the spin chirality. Eventually, the spin correlation is expected to develop into a unique spin-solid-state-density ground state, manifested by the distribution of the pairs of vortex states of opposite chirality. In this paper we report the creation of an artificial permalloy honeycomb lattice of ultrasmall connecting bonds, with a typical size of ${\simeq}12$ nm. Detailed magnetic and neutron-scattering measurements on the newly fabricated honeycomb lattice demonstrate the evolution of magnetic correlation as a function of temperature. Finally, at low enough temperature, neutron-scattering measurements and micromagnetic simulation suggest the development of a loop state of vortex configuration in this system.
New Description of Evolution of Magnetic Phases in Artificial Honeycomb Lattice
Artificial magnetic honeycomb lattice provides a two-dimensional archetypal system to explore novel phenomena of geometrically frustrated magnets. According to theoretical reports, an artificial magnetic honeycomb lattice is expected to exhibit several phase transitions to unique magnetic states as a function of reducing temperature. Experimental investigations of permalloy artificial honeycomb lattice of connected ultra-small elements, ≃ 12 nm, reveal a more complicated behavior. First, upon cooling the sample to intermediate temperature, T≃ 175 K, the system manifests a non-unique state where the long range order co-exists with short-range magnetic charge order and weak spin ice state. Second, at much lower temperature, T≃ 6 K, the long-range spin solid state exhibits a re-entrant behavior. Both observations are in direct contrast to the present understanding of this system. New theoretical approaches are needed to develop a comprehensive formulation of this two dimensional magnet.