12 research outputs found
Experimental signatures of quantum and topological states in frustrated magnetism
Frustration in magnetic materials arising from competing exchange
interactions can prevent the system from adopting long-range magnetic order and
can instead lead to a diverse range of novel quantum and topological states
with exotic quasiparticle excitations. Here, we review prominent examples of
such emergent phenomena, including magnetically-disordered and extensively
degenerate spin ices, which feature emergent magnetic monopole excitations,
highly-entangled quantum spin liquids with fractional spinon excitations,
topological order and emergent gauge fields, as well as complex particle-like
topological spin textures known as skyrmions. We provide an overview of recent
advances in the search for magnetically-disordered candidate materials on the
three-dimensional pyrochlore lattice and two-dimensional triangular, kagome and
honeycomb lattices, the latter with bond-dependent Kitaev interactions, and on
lattices supporting topological magnetism. We highlight experimental signatures
of these often elusive phenomena and single out the most suitable experimental
techniques that can be used to detect them. Our review also aims at providing a
comprehensive guide for designing and investigating novel frustrated magnetic
materials, with the potential of addressing some important open questions in
contemporary condensed matter physics
High-pressure behavior of superconducting boron-doped diamond
This work investigates the high-pressure structure of freestanding
superconducting ( = 4.3\,K) boron doped diamond (BDD) and how it affects
the electronic and vibrational properties using Raman spectroscopy and x-ray
diffraction in the 0-30\,GPa range. High-pressure Raman scattering experiments
revealed an abrupt change in the linear pressure coefficients and the grain
boundary components undergo an irreversible phase change at 14\,GPa. We show
that the blue shift in the pressure-dependent vibrational modes correlates with
the negative pressure coefficient of in BDD. The analysis of x-ray
diffraction data determines the equation of state of the BDD film, revealing a
high bulk modulus of =51028\,GPa. The comparative analysis of
high-pressure data clarified that the sp carbons in the grain boundaries
transform into hexagonal diamond.Comment: 7 pages, 4 figure
Spin re-orientation induced anisotropic magnetoresistance switching in LaCoNiO thin films
Realization of novel functionalities by tuning magnetic interactions in rare
earth perovskite oxide thin films opens up exciting technological prospects.
Strain-induced tuning of magnetic interactions in rare earth cobaltates and
nickelates is of central importance due to their versatility in electronic
transport properties. Here we reported the spin re-orientation induced
switching of anisotropic magnetoresistance (AMR) and its tunability with strain
in epitaxial LaCoNiO thin films across the
ferromagnetic transition. Moreover, with strain tuning, we could observe a
two-fold to four-fold symmetry crossover in AMR across the magnetic transition
temperature. The magnetization measurements revealed an onset of ferromagnetic
transition around 50 K, and a further reduction in temperature showed a subtle
change in the magnetization dynamics, which reduced the ferromagnetic
long-range ordering and introduced glassiness in the system. X-ray absorption
and X-ray magnetic circular dichroism spectroscopy measurements over Co and Ni
L edges revealed the Co spin state transition below the magnetic transition
temperature leading to the AMR switching and also the presence of Ni and
Co ions evidencing the charge transfer from Ni to Co ions. Our work
demonstrated the tunability of magnetic interactions mediated electronic
transport in cobaltate-nickelate thin films, which is relevant in understanding
Ni-Co interactions in oxides for their technological applications such as in
AMR sensors
Spin-liquid-like state in a square lattice antiferromagnet
Collective behavior of spins, frustration-induced strong quantum fluctuations
and subtle interplay between competing degrees of freedom in quantum materials
can lead to correlated quantum states with fractional excitations that are
essential ingredients for establishing paradigmatic models and have immense
potential for quantum technologies. Quenched randomness is a new paradigm in
elucidating the emergence of spin-liquidlike states in geometrically frustrated
magnets. Herein, we report magnetization, specific heat, electron spin
resonance, and muon spin resonance studies on a 3d-electron-based square
lattice antiferromagnet Sr3CuTa2O9. In this material, S = 1/2 Cu2+
nearest-neighbor ions constitute a two-dimensional square lattice. The negative
value of Curie-Weiss temperature, obtained from the Curie-Weiss fit of
high-temperature magnetic susceptibility data indicates the presence of
antiferromagnetic interaction between Cu2+ moments. Specific heat data show the
absence of long-range magnetic ordering down to 64 mK despite a reasonably
strong exchange interaction between Cu2+ spins as reflected from a Curie-Weiss
temperature of -27 K. The power-law behavior and the data collapse of specific
heat and magnetization data evince the emergence of a random-singlet state in
Sr3CuTa2O9. The power-law-like spin auto-correlation function and the data
collapse of muon polarization asymmetry with longitudinal field dependence of
t/({\mu}0H){\gamma} further support credence to the presence of a
randomness-induced liquid-like state. Our results suggest that randomness
induced by disorder is a viable route to realize quantum spin liquid-like state
in this square lattice antiferromagnet
Signature of a randomness-driven spin-liquid state in a frustrated magnet
Collective behaviour of electrons, frustration induced quantum fluctuations
and entanglement in quantum materials underlie some of the emergent quantum
phenomena with exotic quasi-particle excitations that are highly relevant for
technological applications. Herein, we present our thermodynamic and muon spin
relaxation measurements, complemented by ab initio density functional theory
and exact diagonalization results, on the recently synthesized frustrated
antiferromagnet Li4CuTeO6, in which Cu2+ ions (S = 1/2) constitute disordered
spin chains and ladders along the crystallographic [101] direction with weak
random inter-chain couplings. Our thermodynamic experiments detect neither
long-range magnetic ordering nor spin freezing down to 45 mK despite the
presence of strong antiferromagnetic interaction between Cu2+ moments leading
to a large effective Curie-Weiss temperature of -154 K. Muon spin relaxation
results are consistent with thermodynamic results. The temperature and magnetic
field scaling of magnetization and specific heat reveal a data collapse
pointing towards the presence of random-singlets within a disorder-driven
correlated and dynamic ground-state in this frustrated antiferromagnet
Enhanced electron-phonon coupling and critical current density in rapid thermally quenched MgB2 bulk samples
We report Rapid Thermal Quenching (RTQ) studies on MgB2 samples from optimized sintering temperature of 800 °C down to liquid nitrogen temperature with different sintering duration. Superior electron-phonon coupling strength (λe−E2g), critical current density (Jc) and irreversibility fields (Hirr) compared to doped MgB2 were observed without compromising transition temperature Tc. Structural studies showed a contraction of the unit cell due to thermal stress induced by RTQ. Enhanced λe−E2g evaluated from line width, and phonon frequency of Raman spectra using Allen equation was consistent with structural and magnetic studies. Microstructural analysis showed a decrease in grain size resulting in increased Jc and Hirr
Tunable and enhanced Rashba spin-orbit coupling in iridate-manganite heterostructures
10.1103/PhysRevB.102.125145Physical Review B1021212514