Vacancy defects in disordered magnetic materials are known to act as effective spins, ``quasispins'', in response to an external magnetic field. In the dilute limit, the contributions of such ``quasispins'' to the magnetic susceptibility $\chi_\text{vac}(T)\propto N_\text{vac}/T$ are singular in the limit of low temperatures $T$ and match those of free spins. With increasing the density of vacancies, their interactions may become essential. Motivated by frustrated and quasi-one-dimensional magnetic materials, we study analytically quasispins and their interactions in a generic system that has short-range antiferromagnetic order and lacks long-range order. We predict that if the vacancy defect does not disrupt the short-range antiferromagnetic order around it, the quasispin value matches the value of spins of the magnetic atoms in the material, and the correlators of the quasispins of different vacancies match the spin-spin correlators in the vacancy-free material. We confirm our conclusions by exact calculations for Ising chains with nearest-neighbour and next-to-nearest-neighbour interactions. We also compute the first virial correction to the susceptibility of a magnetic material due to the interactions of vacancy quasispins.

Sufficiently clean geometrically frustrated (GF) magnets are the largest class of candidate materials that may host quantum spin liquids (QSLs). Some of them have been shown to exhibit spin-glass freezing, potentially precluding QSLs, at the "hidden energy scale", which is significantly lower than the microscopic energy scale of spin interactions. Here, we investigate the origin of the hidden energy scale and its relationship to the f-ratio, the figure of merit for the degree of frustration in GF magnetic materials. The available experimental and numerical data provide evidence that GF magnets display, universally, two distinct temperature scales in the specific heat, the lowest of which is of the order of the hidden energy scale T^*. We argue that this scale is determined by non-magnetic excitations, similar to spin exchanges in chains of spins. The collective entropy of such excitations matches the entropy of the ground states of the Ising model on the same lattice, which provides a way to verify the proposed scenario in experiment. We demonstrate that in the presence of quenched disorder, a broad class of materials exhibits spin-glass freezing at temperatures of order T^*, in accordance with experimental observations. As T^* is a property of the clean GF medium, it leads to a constraint on the f-ratio.

The anisotropic spin-glass transition, in which spin freezing is observed only along the c axis in pseudobrookite Fe2TiO5, has long been perplexing because the Fe3+ moments (d5) are expected to be isotropic. Recently, neutron diffraction demonstrated that surfboard-shaped antiferromagnetic nanoregions coalesce above the glass transition temperature Tg approximate to 55 K, and a model was proposed in which the freezing of the surfboard magnetization fluctuations leads to the anisotropic spin-glass state. Given this model, we have carried out high resolution inelastic neutron scattering measurements of the spin-spin correlations to understand the temperature dependence of the intrasurfboard spin dynamics on neutron (picosecond) timescales. Here, we report on the temperature-dependence of the spin fluctuations measured from single-crystal Fe2TiO5. Strong quasi-elastic magnetic scattering, arising from intrasurfboard correlations, is observed well above Tg. The spin fluctuations possess a steep energy-wave vector relation and are indicative of strong exchange interactions, consistent with the large Curie-Weiss temperature. As the temperature approaches Tg from above, a shift in spectral weight from inelastic to elastic scattering is observed. At various temperatures between 4 and 300 K, a characteristic relaxation rate of the fluctuations is determined. Despite the freezing of most of the spin correlations, an inelastic contribution remains even at base temperature, signifying the presence of fluctuating intrasurfboard spin correlations to at least T/Tg approximate to 0.1, consistent with an energy landscape that is a hybrid between conventional and geometrically frustrated spin glasses.

Motivated by frustrated magnets and quasi-one-dimensional magnetic materials, we study the magnetic properties of 1D Ising chains with nearest-neighbour (NN) and weaker next-to-nearest neighbour (NNN) interactions in the presence of vacancy defects. The effect of a vacancy on the magnetic susceptibility of a spin chain is two-fold: it reduces the length of the chain by an effective ``vacancy size'' and may also act as a free spin, a ``quasispin'', with a Curie-type $\chi_\text{quasi}=\langle S^2\rangle/T$ contribution to the susceptibility. In chains with antiferromagnetic short-range order, the susceptibility of vacancy-free chains is exponentially suppressed at low temperatures, and quasispins dominate the effect of impurities on the chains' magnetic properties. For chains with antiferromagnetic NN interactions, the quasispin matches the value $\langle S^2\rangle=1$ of the Ising spins in the chain for ferromagnetic NNN interactions and vanishes for antiferromagnetic NNN interactions. For chains with ferromagnetic short-range order, quasispin effects are insignificant due to exponentially large low-temperature susceptibilities, and the dominant effect of a vacancy is effectively changing the length of the chain.

The unusual anisotropy of the spin glass transition in the pseudobrookite system Fe_2TiO_5 has been interpreted as arising from an induced, van der Waals-like, interaction among magnetic clusters. Here we present susceptibility (χ) and specific heat data (C) for Fe2TiO5 diluted with non-magnetic Ga, (Fe_1-pGa_p)_2TiO_5, for disorder parameter p = 0, 0.11, and 0.42, and elastic neutron scattering data for p = 0.20. A uniform suppression of T_g is observed upon increasing p, along with a value of χ (T_g) that increases as T_g decreases, i.e. dχ(T_g)/dT_g< 0. We also observe C(T) ∝ T^2 in the low temperature limit. The observed behavior places (Fe_1-pGa_p)_2TiO_5 in the category of a strongly geometrically frustrated spin glass.

The unusual anisotropy of the spin glass (SG) transition in the pseudobrookite system Fe 2 TiO 5 has been interpreted as arising from an induced, van der Waals-like, interaction among magnetic clusters. Here we present susceptibility ( χ ) and specific heat data ( C ) for Fe 2 TiO 5 diluted with non-magnetic Ga, (Fe 1− p Ga p ) 2 TiO 5 , for disorder parameter p = 0, 0.11, and 0.42, and elastic neutron scattering data for p = 0.20. A uniform suppression of T g is observed upon increasing p , along with a value of χ T g that increases as T g decreases, i.e. d χ ( T g ) / d T g < 0 We also observe C T ∝ T 2 in the low temperature limit. The observed behavior places (Fe 1− p Ga p ) 2 TiO 5 in the category of a strongly geometrically frustrated SG.

We report measurements of the low-temperature specific heat of Al-flux-grown samples of SmB$_6$ in magnetic fields up to 32 T. Quantum oscillations periodic in $1/H$ are observed between 8 and 32 T at selected angles between [001] and [111]. The observed frequencies and their angular dependence are consistent with previous magnetic torque measurements of SmB$_6$ but the effective masses inferred from Lifshitz-Kosevich theory are significantly larger and closer to those inferred from zero-field specific heat. Our results are thus consistent with a bulk density of states origin for the oscillations.

Despite the enormous interest in quantum spin liquids, their experimental existence still awaits broad consensus. In particular, quenched disorder may turn a specific system into a spin glass and possibly preclude the formation of a quantum spin liquid. Here, we demonstrate that the glass transition among geometrically frustrated magnets, a materials class in which spin liquids are expected, differs qualitatively from conventional spin glass. Whereas conventional systems have a glass temperature that increases with increasing disorder, geometrically frustrated systems have a glass temperature that increases with decreasing disorder, approaching, in the clean limit, a finite value. This behaviour implies the existence of a hidden energy scale (far smaller than the Weiss constant) which is independent of disorder and drives the glass transition in the presence of disorder. Motivated by these observations, we propose a scenario in which the interplay of interactions and entropy in the disorder-free system yields a temperature-dependent magnetic permeability with a crossover temperature that determines the hidden energy scale. The relevance of this scale for quantum spin liquids is discussed.

We investigate the spin-glass transition in the strongly frustrated well-known compound Fe2TiO5. A remarkable feature of this transition, widely discussed in the literature, is its anisotropic properties: The transition manifests itself in the magnetic susceptibly only along one axis, despite Fe3+ d(5) spins having no orbital component. We demonstrate, using neutron scattering, that below the transition temperature T-g = 55 K, Fe2TiO5 develops nanoscale surfboard-shaped antiferromagnetic regions in which the Fe3+ spins are aligned perpendicular to the axis which exhibits freezing. We show that the glass transition may result from the freezing of transverse fluctuations of the magnetization of these regions and we develop a mean-field replica theory of such a transition, revealing a type of magnetic van der Waals effect.

Nontrivial electron band structures may enable a new generation of functional materials.

The plateau at $1/3$ of the saturation magnetization ${M}_{s}$ in the metamagnet CeSb is accompanied by a state of ferromagnetic layers of spins in an up-up-down sequence. We measured $M$ and the specific heat $C$ in the plateau, spin wave analyses of which reveal two distinct branches of excitations. Those with $\mathrm{\ensuremath{\Delta}}{S}_{z}=1$ as measured by $M$, coexist with a much larger population of $\mathrm{\ensuremath{\Delta}}{S}_{z}=0$ excitations measured by $C$ but invisible to $M$. The large density of $\mathrm{\ensuremath{\Delta}}{S}_{z}=0$ excitations, their energy gap, and their seeming lack of interaction with $\mathrm{\ensuremath{\Delta}}{S}_{z}=1$ excitations suggest an analogy with astrophysical dark matter. Additionally, in the middle of the plateau three sharp jumps in $M(H)$ are seen, the size of which, $0.15%{M}_{s}$, is consistent with fractional quantization of magnetization per site in the down-spin layers.

La0.4Ce0.6Co2P2 represents a borderline case in the range of solid solutions formed in the pseudobinary system LaCo2P2-CeCo2P2. The material undergoes ferromagnetic ordering at similar to 225 K followed by a structural collapse at similar to 190 K, which leads to a strong suppression of magnetization. The structural phase transition manifests itself in a gradual decrease in the parameter c and a relatively smaller increase of the parameter a of the tetragonal lattice. Interestingly, a combination of magnetic measurements and nonpolarized and polarized neutron scattering experiments suggests that the structural collapse does not lead to an antiferromagnetically ordered state, observed in samples with the higher Ce content. On the contrary, La0.4Ce0.6Co2P2 appears to enter a disordered, spin glass state, with gradual dissipation of the ferromagnetic ordering taking place simultaneously with the structural collapse, as evidenced by temperature-dependent measurements of the depolarization factor for a polarized neutron beam passing through the sample. The observed behavior is analogous to that reported for so-called reentrant spin glasses. In the present case, however, the appearance of the reentrant spin glass regime is caused not by tuning the chemical composition but by the structural phase transition. Electronic structure calculations confirm that the loss of magnetic ordering is caused by the subtle change to the density of states at the Fermi level due to the variation of the crystal structure of the material.

The plateau at 1/3 of the saturation magnetization M_{s} in the metamagnet CeSb is accompanied by a state of ferromagnetic layers of spins in an up-up-down sequence. We measured M and the specific heat C in the plateau, spin wave analyses of which reveal two distinct branches of excitations. Those with ΔS_{z}=1 as measured by M, coexist with a much larger population of ΔS_{z}=0 excitations measured by C but invisible to M. The large density of ΔS_{z}=0 excitations, their energy gap, and their seeming lack of interaction with ΔS_{z}=1 excitations suggest an analogy with astrophysical dark matter. Additionally, in the middle of the plateau three sharp jumps in M(H) are seen, the size of which, 0.15%M_{s}, is consistent with fractional quantization of magnetization per site in the down-spin layers.

Weyl fermions scattering from a random Coulomb potential are predicted to exhibit resistivity versus temperature in a single particle model. Here we show that, in closed-environment-grown polycrystalline samples of Y2Ir2O7, over four orders of magnitude in . While the measured prefactor, , is obtained from the model using reasonable materials parameters, the behavior extends far beyond the model's range of applicability. In particular, the behavior extends into the low-temperature, high-resistivity region where the Ioffe-Regel parameter, . Strong on-site Coulomb correlations, instrumental for predicting a Weyl semimetal state in Y2Ir2O7, are the possible origin of such 'bad' Weyl semimetal behavior.

During the Cold War, Eastern and Western manufacturers found good reasons to collaborate, even on a technology as sensitive as nuclear vessels.

Obesity is a public health problem present in both developed and developing countries. The white adipose tissue (WAT) is the main deposit of lipids when there is an excess of energy. Its pathological growth is directly linked to the development of obesity and to a wide number of comorbidities, such as insulin-resistance, cardiovascular disease, among others. In this scenario, it becomes imperative to develop new approaches to the treatment and prevention of obesity and its comorbidities. It has been documented that the browning of WAT could be a suitable strategy to tackle the obesity epidemic that is developing worldwide. Currently there is an intense search for bioactive compounds with anti-obesity properties, which present the particular ability to generate thermogenesis in the brown adipose tissue (BAT) or beige. The present study provide recent information of the bioactive nutritional compounds capable of inducing thermogenesis and therefore capable of generate positive effects on health.

The 1/8 fractional plateau phase (1/8 FPP) in Shastry-Sutherland lattice (SSL) spin systems has been viewed an exemplar of emergence on an Archimedean lattice. Here we explore this phase in the Ising magnet TmB_{4} using high-resolution specific heat (C) and magnetization (M) in the field-temperature plane. We show that the 1/8 FPP is smoothly connected to the antiferromagnetic phase on ramping the field from H=0. Thus, the 1/8 FPP is not a distinct thermodynamic ground state of TmB_{4}. The implication of these results for Heisenberg spins on the SSL is discussed.

Silica coated magnetite particles (Fe3O4@SiO2) functionalized with gold Fe3O4@SiO2 + Au), or gold plus poly (vinylpyrrolidone) (PVP) (Fe3O4@SiO2 + Au + PVP) were synthesized. Their structural and magnetic properties were studied using a combination of experimental techniques including electron microscopy (EM), superconducting quantum interference device (SQUID) magnetrometry, and electron paramagnetic resonance (EPR) spectroscopy. The saturation magnetization (MS) of particles functionalized with gold and gold plus PVP were found to be 67.24 emu/g and 65.78 emu/g respectively. Both functionalized ensembles maintained a large percentage (78-80%) of their MS values compared to pristine magnetite. The coercivity (HC) for pristine magnetite was 227.25 Gauss compared to 200.00 Gauss for Fe3O4@SiO2 + Au and 228.57 Gauss for Fe3O4@SiO2 + Au + PVP. Furthermore, these magnetic particles, being biologically compatible and resistant to oxidation, were functionalized with an antibody designed to target A431 oral cancer cells. The result demonstrates high specificity of binding compared to non-functionalized particles, attributable to a favorable interaction between gold and the antibody making them excellent candidates for applications like bio-separation and imaging.