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Recently, a new class of magnetic phenomenon, called altermagnetism, was proposed where the underlying spin configuration resembles antiferromagnetic structure, but the system violates \textbf{PT} (PT: Parity times Time reversal) symmetry due to the alternation of crystalline symmetry across magnetic ions. Although the original idea was proposed for the collinear spin structure, a recent report by Cheong et al. has suggested that antiferromagnetic materials with non-collinear spin structure and local alternation of crystalline arrangement can also manifest altermagnetism. Besides breaking the \textbf{PT} symmetry, altermagnetic compounds are also expected to exhibit anomalous Hall effects of odd orders. Here, we discuss possible candidates in this regard. One example is nickel monosilicide, which was recently shown to exhibit high temperature antiferromagnetism with non-collinear spin structure. It fulfills both criteria of breaking the \textbf{PT} symmetry and manifesting nonlinear anomalous Hall effect. In addition to NiSi, we also discuss other potential antiferromagnetic materials with non-collinear spin configuration for the exploration of altermagnetic states., Comment: 13 pages, 13 figures, perspective

Topological magnetic charges, arising due to the non-vanishing magnetic flux on spin ice vertices, serve as the origin of magnetic monopoles that traverse the underlying lattice effortlessly. Unlike spin ice materials of atomic origin, the dynamic state in artificial honeycomb spin ice is conventionally described in terms of finite size domain wall kinetics that require magnetic field or current application. Contrary to this common understanding, here we show that thermally tunable artificial permalloy honeycomb lattice manifests a perpetual dynamic state due to self-propelled magnetic charge defect relaxation in the absence of any external tuning agent. Quantitative investigation of magnetic charge defect dynamics using neutron spin echo spectroscopy reveals sub-ns relaxation times that are comparable to monopole's relaxation in bulk spin ices. Most importantly, the kinetic process remains unabated at low temperature where thermal fluctuation is negligible. This suggests that dynamic phenomena in honeycomb spin ice are mediated by quasi-particle type entities, also confirmed by quantum Monte-Carlo simulations that replicate the kinetic behavior. Our research unveils a new `macroscopic' magnetic particle that shares many known traits of quantum particles, namely magnetic monopole and magnon., Comment: 12 figures, 15 pages

The observation of magnetic diode behavior with ultra-low forward voltage of 5 mV renders new venue for energetically efficient spintronic device research in the unconventional system of two-dimensional permalloy honeycomb lattice. Detailed understanding of temperature and magnetic field tuning of diode behavior is imperative to any practical application. Here, we report a comprehensive study in this regard by performing electrical measurements on magnetic diode sample as functions of temperature and magnetic field. Magnetic diode is found to persist across the broad temperature range. Magnetic field application unveils a peculiar reentrant characteristic where diode behavior is suppressed in remnant field but reappears after warming to room temperature. Analysis of I-V data suggests a modest energy gap, 0.03-0.1 eV, which is comparable to magnetic Coulomb's interaction energy between emergent magnetic charges on honeycomb vertices in the reverse biased state. It affirms the role of magnetic charge correlation in unidirectional conduction in 2D honeycomb lattice. The experimental results are expected to pave way for the utilization of magnetic diode in next generation spintronic device applications., Comment: 7 pages, 5 figures

Ruthenates provide comprehensive platform to study a plethora of novel properties, such as quantum magnetism, superconductivity and magnetic fluctuation mediated metal-insulator transition. In this article, we provide an overview of quantum mechanical phenomenology in calcium ruthenium oxide with varying compositions. While the stochiometric composition of CaRuO$_{3}$ exhibits non-Fermi liquid behavior with quasi-criticality, chemically doped compounds depict prominent signatures of quantum magnetic fluctuations at low temperature that in some cases are argued to mediate in metal-insulator transition. In the case of cobalt doped- CaRuO$_{3}$, an unusual continuum fluctuation is found to persist deep inside the glassy phase of the material. These observations reflect the richness of ruthenate research platform in the study of quantum magnetic phenomena of fundamental importance., Comment: 7 pages, 8 figures

Spin diode is important prerequisite to practical manifestation of spin electronics. Yet, a functioning magnetic diode at room temperature is still illusive. Here, we reveal diode-type phenomena due to magnetic charge mediated conduction in artificial honeycomb geometry, made of concave shape single domain permalloy element. We find that honeycomb lattice defies symmetry by populating vertices with low and high multiplicity magnetic charges, causing asymmetric magnetization, in applied current of opposite polarity. High multiplicity units create highly resistive network, thereby inhibiting magnetic charge dynamics propelled electrical conduction. However, practical realization of this effect requires modest demagnetization factor in constituting element. Concave structure fulfills the condition. Subsequently, magnetic diode behavior emerges across broad thermal range of $T$ = 40K - 300K. The finding is a departure from the prevailing notion of spin-charge interaction as the sole guiding principle behind spintronics. Consequently, a new vista, mediated by magnetic charge interaction, is envisaged for spintronic research, Comment: 4 figures

The emergent concept of magnetic charge quasi-particle provides a new realm to study the evolution of magnetic properties in two-dimensional artificially frustrated magnets. We report on the exploration of magnetic phases due to various magnetic charge correlation using the complementary numerical techniques of micromagnetic and distorted wave Born approximation simulations in artificial permalloy honeycomb lattice. The honeycomb element length varies between 10 nm and 100 nm, while the width and thickness are kept within the single domain limit. In addition to the charge ordered loop state, we observe disordered charge arrangement, characterized by the random distribution of $\pm$Q charges, in single domain size honeycomb lattice. As the length of honeycomb element increases, low multiplicity magnetic charges tend to form contiguous bands in thinner lattice. Thin honeycomb lattice with 100 nm element length exhibits a perfect spin ice pattern, which remains unaffected to the modest increase in the width of element size. We simulate scattering profiles under the pretext of distorted wave Born approximation formalism for the micromagnetic phases. The results are expected to provide useful guidance in the experimental investigation of magnetic phases in artificial honeycomb magnet., Comment: 9 pages, 6 figures

A quantum magnetic state due to magnetic charges is never observed, even though they are treated as quantum mechanical variable in theoretical calculations. Here, we demonstrate the occurrence of a novel quantum disordered state of magnetic charges in nanoengineered magnetic honeycomb lattice of ultra-small connecting elements. The experimental research, performed using spin resolved neutron scattering, reveals a massively degenerate ground state, comprised of low integer and energetically forbidden high integer magnetic charges, that manifests cooperative paramagnetism at low temperature. The system tends to preserve the degenerate configuration even under large magnetic field application. It exemplifies the robustness of disordered correlation of magnetic charges in 2D honeycomb lattice. The realization of quantum disordered ground state elucidates the dominance of exchange energy, which is enabled due to the nanoscopic magnetic element size in nanoengineered honeycomb. Consequently, an archetypal platform is envisaged to study quantum mechanical phenomena due to emergent magnetic charges.

Emerging new concepts, such as magnetic charge dynamics in two-dimensional magnetic material, can provide novel mechanism for spin based electrical transport at macroscopic length. In artificial spin ice of single domain elements, magnetic charge's relaxation can create an efficient electrical pathway for conduction by generating fluctuations in local magnetic field that couple with conduction electrons spins. In a first demonstration, we show that the electrical conductivity is propelled by more than an order of magnitude at room temperature due to magnetic charge defects sub-picosecond relaxation in artificial magnetic honeycomb lattice. The direct evidence to the proposed electrical conduction mechanism in two-dimensional frustrated magnet points to the untapped potential for spintronic applications in this system.

I briefly mention a previous claim of room temperature superconductivity ( arXiv:0905.3524) in Ag-based oxide material and compare their results with the most recent claim of ambient temperature superconductivity in arXiv:1807.08572. In both cases, an electrical transition to low resistance state and diamagnetism are observed. Silver is a common ingredient in both claims. Does it mean that silver holds the key to RT superconductivity or, the missing field cool data (in both reports) hint of some other physical phenomenon than superconductivity., Comment: 2 pages, 1 figure, regarding new arXiv report of arXiv:1807.08572

We report detailed experimental investigation of the transport and magnetic properties of orthorhombic NiSi along with first principles studies of this phase and related nickel silicides. Neutron scattering shows no evidence for magnetism, in agreement with first principles calculations. Comparison of first principles results and experimental results from our measurements and literature show a weak electron phonon coupling. We discuss transport and other properties of NiSi and find behavior characteristic of a weak correlated metal far from magnetism. Trends among the nickel silicides as a function of nickel content are discussed.

Hexagonal Dy(0.5)Y(0.5)MnO3, a multiferroic rare-earth manganite with geometrically frustrated antiferromagnetism, has been investigated with single-crystal neutron diffraction measurements. Below 3.4 K magnetic order is observed on both the Mn (antiferromagnetic) and Dy (ferrimagnetic) sublattices that is identical to that of undiluted hexagonal DyMnO3 at low temperature. The Mn moments undergo a spin reorientation transition between 3.4 K and 10 K, with antiferromagnetic order of the Mn sublattice persisting up to 70 K; the antiferromagnetic order in this phase is distinct from that observed in undiluted (h)DyMnO3, yielding a qualitatively new phase diagram not seen in other hexagonal rare-earth manganites. A magnetic field applied parallel to the crystallographic c axis will drive a transition from the antiferromagnetic phase into the low-temperature ferrimagnetic phase with little hysteresis., Comment: Six pages, four figures v2: Table I added, Figures 2 and 3 edited, text edited. August 24, 2011

The Zn-paratacamite family, Zn$_{x}$Cu$_{4-x}$(OH)$_{6}$Cl$_{2}$ for $x \, \geq$ 0.33, is an ideal system for studying spin-1/2 frustrated magnetism in the form of antiferromagnetic Cu$^{2+}$ kagome planes. Here we report a new synthesis method by which high quality millimeter-sized single crystals of Zn-paratacamite have been produced. These crystals have been characterized by metal analysis, x-ray diffraction, neutron diffraction, and thermodynamic measurements. The $x$ = 1 member of the series displays a magnetic susceptibility that is slightly anisotropic at high temperatures with $\chi_{c} \, > \, \chi_{ab}$. Neutron and synchrotron x-ray diffraction experiments confirm the quality of these $x$ = 1 single crystals and indicate no obvious structural transition down to temperatures of T=2 K., Comment: 4 pages, 3 figures, accepted by PRB rapid communication

Arrays of nanoscopic magnetic asymmetric rings, 150 nm in outer diameter, are fabricated using the techniques of electron-beam lithography, angular deposition and ion-beam etching. Magnetic measurements for cobalt asymmetric rings at room temperature verifies previous reports of vortex magnetic state formation of a desired circulation direction for the application of external magnetic field along the asymmetry axis of the rings. However, the main theme of this article is the observation of exchange bias phenomena when the ring samples are cooled down to low temperature in the presence of a positive magnetic field. Very interestingly, the observed exchange bias effect is negative for along and perpendicular orientations of ring's asymmetry axis with respect to the in-plane external magnetic field. This is in good quantitative agreement with the random interface model proposed by Malozemoff et al. For the application of inplane external magnetic field at 45 degree with respect to the asymmetry axis, the exchange bias effect is positive. Unlike the exchange bias effects in thin films, this is a very unusual observation indicating that exchange bias phenomena of opposite natures can be manipulated by appropriate combination of geometrical constraint and external magnetic field direction, in addition to the interfacial interactions between ferromagnetic (FM) and antiferromagnetic (AFM) layer., Comment: Asymmetric magnetic rings arrays; Exchange bias phenomena

In this article, we report on experimental and theoretical investigations of magnetic transitions in cobalt rings of size (diameter, width and thickness) comparable to the exchange length of cobalt. Magnetization measurements were performed for two sets of magnetic ring arrays: ultra-small magnetic rings (outer diameter 13 nm, inner diameter 5nm and thickness 5 nm) and small thin-walled magnetic rings (outer diameter 150 nm, width 5 nm and thickness 5 nm). This is the first report on the fabrication and magnetic properties of such small rings. Our calculations suggest that if the magnetic ring's sizes are comparable to, or smaller than, the exchange length of the magnetic material, then only two magnetic states are important - the pure single domain state and the flux closure vortex state. The onion-shape magnetic state does not arise. Theoretical calculations are based on an energetic analysis of pure and slightly distorted single domain and flux closure vortex magnetic states. Based on the analytical calculations, a phase diagram is also derived for ultra-small ring structures exhibiting the region for vortex magnetic state formations as a function of material parameter., Comment: 10 pages, 15 figures