Super Spin Research Articles

Modeling public opinion control by a charismatic leader

We study the average long-time behavior of the binary opinions of a social group with peer-to-peer interactions under the influence of an external bias and a persuadable leader, a strongly-biased agent with a dynamic opinion with the intention of spreading it across the system. We use a generalized, fully-connected Ising model, with each spin representing the binary opinion of an agent at a given time and a single, super spin representing the opinion of the leader. External fields and interaction constants model the opinion bias and peer-to-peer interactions, respectively, while the temperature T models an idealized social climate, representing an authoritarian regime if T is low or a liberal one if T is high. We derive a mean-field solution for the average magnetization m, the “social mood”, and investigate how m and the super spin magnetization vary as a function of T. We find that, depending on the initial conditions, due to the presence of metastable states, the sign of the average magnetization depends on the temperature. Finally, we verify that this effect is also present even if we consider only nearest-neighbor interactions within the social group.

Folding QQ-relations and transfer matrix eigenvalues: Towards a unified approach to Bethe ansatz for super spin chains

Extending the method proposed in [1], we derive QQ-relations (functional relations among Baxter Q-functions) and T-functions (eigenvalues of transfer matrices) for fusion vertex models associated with the twisted quantum affine superalgebras Uq(gl(2r+1|2s)(2)), Uq(gl(2r|2s+1)(2)), Uq(gl(2r|2s)(2)), Uq(osp(2r|2s)(2)) and the untwisted quantum affine orthosymplectic superalgebras Uq(osp(2r+1|2s)(1)) and Uq(osp(2r|2s)(1)) (and their Yangian counterparts, Y(osp(2r+1|2s)) and Y(osp(2r|2s))) as reductions (a kind of folding) of those associated with Uq(gl(M|N)(1)). In particular, we reproduce previously proposed generating functions (difference operators) of the T-functions for the symmetric or anti-symmetric representations, and tableau sum expressions for more general representations for orthosymplectic superalgebras [2,3], and obtain Wronskian-type expressions (analogues of Weyl-type character formulas) for them. T-functions for spinorial representations are related to reductions of those for asymptotic limits of typical representations of Uq(gl(M|N)(1)).

Investigation of structural phase stability, modified magnetic spin order and low temperature spin glass-like phase transitions in Sc-doped M-type BaFe12O19 hexaferrite

This work used two approaches of mechanical alloying before high temperature solid state reaction to synthesize BaFe12-xScxO19 (x = 0.5 to 6.0) system. Rietveld refinement of X-ray diffraction patterns showed the formation of extra phases at higher Sc doping, along with the main magnetoplumbite structure. Raman spectroscopy suggested random distribution of Sc ions at the Fe-sites of hexaferrite structure. X-ray photoelectron spectroscopy (XPS) confirmed the +3 charge state at the Fe/Sc-sites. The Fe 3s band suggested dilution of ferromagnetic 3s-3d spin exchange interactions. The neutron diffraction study re-confirmed random occupancy of the non-magnetic Sc3+ ions at Fe3+ sites of the Sc doped Ba hexaferrite system. The transformation of magnetic spin order from collinear to non-collinear state has shown spin glass-like features at low temperature regime in the dc magnetization curves. This is an effect of dilution of Fe–O–Fe ferrimagnetic super exchange interactions and spin frustration in Sc-doped samples.

Overlaps and fermionic dualities for integrable super spin chains

The mathfrak{psu}left(2,left.2right|4right) integrable super spin chain underlying the AdS/CFT correspondence has integrable boundary states which describe set-ups where k D3-branes get dissolved in a probe D5-brane. Overlaps between Bethe eigenstates and these boundary states encode the one-point functions of conformal operators and are expressed in terms of the superdeterminant of the Gaudin matrix that in turn depends on the Dynkin diagram of the symmetry algebra. The different possible Dynkin diagrams of super Lie algebras are related via fermionic dualities and we determine how overlap formulae transform under these dualities. As an application we show how to consistently move between overlap formulae obtained for k = 1 from different Dynkin diagrams.

Spin transition mechanism in a cooperatively assembled Al/Fe-doped 2D SiC based on electric field manipulation

Abstract The spin transition mechanism in an SiC monolayer doped with Al/Fe artificial monolayer was analysed using a tuneable perpendicular electric field. The spin-valve gate voltage, −0.2/0.4 eV, is asymmetrical owing to out-of-plane spin order with asymmetrical spin accumulation, which is generally distributed in a honeycomb energy structure. The spin transport process—excited, exchanging, and inverted—was observed in the density of states for the tuneable outward-propagating electric field, resulting in super spin transport between Al and Fe atoms. The Fermi velocity was used to explore the dynamic interaction of the spin and the electric field, which was exhibited by their spin texture. The role of electronic correlation effects and the electronic coupling to magnetic excitations is discussed in view of the spin texture. Our results present an active spin order dynamic scene in SiC monolayer doped with Al/Fe artificial microstructure under electric field, which sheds light on manipulating spin information, in particular, for designing spin valves for spin devices.

Exploring the Different Degrees of Magnetic Disorder in TbxR1-xCu2 Nanoparticle Alloys.

Recently, potential technological interest has been revealed for the production of magnetocaloric alloys using Rare-Earth intermetallics. In this work, three series of TbRCu (R ≡ Gd, La, Y) alloys have been produced in bulk and nanoparticle sizes via arc melting and high energy ball milling. Rietveld refinements of the X-ray and Neutron diffraction patterns indicate that the crystalline structure in all alloys is consistent with TbCu orthorhombic bulk crystalline structure. The analyses of the DC-magnetisation () and AC-susceptibility () show that three distinct degrees of disorder have been achieved by the combination of both the Tb replacement (dilution) and the nanoscaling. These disordered states are characterised by transitions which are evident to , and specific heat. There exists an evolution from the most ordered Superantiferromagnetic arrangement of the TbLaCu NPs with Néel temperature, 27 K, and freezing temperature, 7 K, to the less ordered weakly interacting Superparamagnetism of the TbYCu nanoparticles ( absent, and T 3 K). The Super Spin Glass TbGdCu nanoparticles ( absent, and 20 K) are considered an intermediate disposition in between those two extremes, according to their enhanced random-bond contribution to frustration.

Search for high temperature memory effects in magnetic nanoparticles

Nanoparticle materials have become a promising candidate for a new kind of storage media based on thermally induced memory effects due to the possibility to tailor their magnetic properties and behaviour. In this study, we have investigated whether the magnetic memory effects could appear at high, industry accessible temperatures including the possibility of thermal data inscription. Investigated iron oxide nanoparticles were synthesized by poliol method, which has been modified in order to allow control of particle agglomeration and consequently magnetic properties. Structure, morphology and the degree of nanoparticle agglomeration were studied by X-Ray diffraction, Transmission Electron Microscopy and Dynamic Light Scattering techniques, while magnetic properties as well as memory effects were measured on a commercial SQUID-based magnetometer. Results of the study confirmed that in super spin glass magnetite nanoparticles, magnetic memory effects can be observed up to 200 K which represents much higher temperatures in comparison to those achieved in spin glasses and other glassy materials. Procedures of writing and reading (inscribing and retrieving) of digital information in such a material were demonstrated and discussed in details.

Lattice strain accommodation and absence of pre-transition phases in Ni50Mn25+x In25−x

The stoichiometric Ni50Mn25In25 Heusler alloy transforms from a stable ferromagnetic austenitic ground state to an incommensurate modulated martensitic ground state with a progressive replacement of In with Mn without any pre-transition phases. The absence of pre-transition phases like strain glass in Ni50Mn25+x In25−x alloys is explained to be the ability of the ferromagnetic cubic structure to accommodate the lattice strain caused by atomic size differences of In and Mn atoms. Beyond the critical value of x = 8.75, the alloys undergo martensitic transformation despite the formation of ferromagnetic and antiferromagnetic clusters and the appearance of a super spin glass state.

Investigating the Size and Microstrain Influence in the Magnetic Order/Disorder State of GdCu2 Nanoparticles.

A series of GdCu nanoparticles with controlled sizes ranging from 7 nm to 40 nm has been produced via high-energy inert-gas ball milling. Rietveld refinements on the X-ray diffraction measurements ensure that the bulk crystalline structure is retained within the nanoparticles, thanks to the employed low milling times ranging from t = 0.5 to t = 5 h. The analysis of the magnetic measurements shows a crossover from Superantiferromagnetism (SAF) to a Super Spin Glass state as the size decreases at NP size of 18 nm. The microstrain contribution, which is always kept below 1%, together with the increasing surface-to-core ratio of the magnetic moments, trigger the magnetic disorder. Additionally, an extra contribution to the magnetic disorder is revealed within the SAF state, as the oscillating RKKY indirect exchange achieves to couple with the aforementioned contribution that emerges from the size reduction. The combination of both sources of disorder leads to a maximised frustration for 25 nm sized NPs.

Asymmetric ascending and descending loop shift exchange bias in Bi2Fe4O9-BiFeO3 nanocomposites

We show detail study of asymmetric exchange bias originating from asymmetric behaviour of ascending and descending loops of the magnetic hysteresis of Bi2Fe4O9-BiFeO3 multiferroics nanocomposites. Detail magnetometry study reveals the co-existence of super spin glass (SSG) and dilute antiferromagnet in a field (DAFF) at the interface between antiferromagnetic (AFM) BiFeO3 and ferromagnetic (FM) Bi2Fe4O9 in nanocomposite particles. The interfacial spins behave differently for positive and negative fields and result into asymmetric exchange bias, which has been precisely identified by several critical magnetic measurements such as training effect, stop & wait protocol, isothermal remanence (IRM) & thermoremanence (TRM) measurements, and high field relaxation measurement. The DAFF spins, which generate non-switchable unidirectional anisotropy at the complex FM-SSG-DAFF-AFM interface below Vogel-Fulcher freezing temperature of BiFeO3 at 29.4 K, are solely responsible for such asymmetry in exchange bias.

Spin cluster size dependence of exchange bias effect in Mn50Ni40Ga10 Heusler alloys

The technique based on exchange bias effect is believed to play a significant role in next-generation spin-involved magnetic devices. However, 60 years after the discovery of the exchange bias, it remains unclear about origin and influencing factors of exchange bias. In this study, a giant exchange bias field of 5132 Oe was introduced in Mn50Ni40Ga10 Heusler alloys at 2 K with a cooling field of 10 kOe. Magnetic measurements showed that the giant exchange bias effect at lower temperature originates from the coupling between super spin glass and antiferromagnetic matrix. Different from previous reports, we elaborated on the issue of cooling field dependence from the perspective of size effect. The size effect was further demonstrated by calculating and comparing the relaxation time of super spin glass under different cooling fields. Although the relationship between particles sizes and relaxation time yet requires further validation, the current proposal can be applied to most exchange bias in Heusler systems.

Superposition of conventional and spontaneous exchange bias in a Ni50Mn34In13Fe3 magnetic shape memory alloy

The conventional exchange bias and spontaneous exchange bias are two interesting but fundamentally different effects in Mn rich Ni-Mn-Z magnetic shape memory alloys. Previous investigations show that these two phenomena appear separately. Here, we report that the conventional and spontaneous exchange bias phenomena coexist in a Ni50Mn34In13Fe3 alloy and the superposition of them increases the total exchange bias of the alloy. Our results suggest that the canonical spin glass and super spin glass may coexist and are embedded in the antiferromagnetic matrix of the martensite, through properly tuning the temperature-field history, which further results in the superposition of conventional and spontaneous exchange bias for this alloy. The interfacial interaction between the canonical spin glass and the antiferromagnetic matrix forms during field cooling process, which results in the conventional exchange bias. Moreover, the application of large magnetic field during the isothermal magnetization process changes the superspin glass into a superferromagnetic state, which interacts with the antiferromagnetic matrix at the interface, causing the spontaneous exchange bias. The superposition of exchange bias provides an effective way to achieve large exchange bias in materials.

Quantum Spectral Curve of γ-Twisted 𝒩 = 4 SYM Theory and Fishnet CFT

We review the quantum spectral curve (QSC) formalism for the spectrum of anomalous dimensions of [Formula: see text] SYM, including its [Formula: see text]-deformation. Leaving aside its derivation, we concentrate on the formulation of the “final product” in its most general form: a minimal set of assumptions about the algebraic structure and the analyticity of the [Formula: see text]-system — the full system of Baxter [Formula: see text]-functions of the underlying integrable model. The algebraic structure of the [Formula: see text]-system is entirely based on (super)symmetry of the model and is efficiently described by Wronskian formulas for [Formula: see text]-functions organized into the Hasse diagram. When supplemented with analyticity conditions on [Formula: see text]-functions, it fixes completely the set of physical solutions for the spectrum of an integrable model. First, we demonstrate the spectral equations on the example of [Formula: see text] and [Formula: see text] Heisenberg (super)spin chains. Supersymmetry [Formula: see text] occurs as a simple “rotation” of the Hasse diagram for a [Formula: see text] system. Then we apply this method to the spectral problem of [Formula: see text]/CFT4-duality, describing the QSC formalism. The main difference with the spin chains consists in more complicated analyticity constraints on [Formula: see text]-functions which involve an infinitely branching Riemann surface and a set of Riemann–Hilbert conditions. As an example of application of QSC, we consider a special double scaling limit of [Formula: see text]-twisted [Formula: see text] SYM, combining weak coupling and strong imaginary twist. This leads to a new type of non-unitary CFT dominated by particular integrable, and often computable, 4D fishnet Feynman graphs. For the simplest of such models — the bi-scalar theory — the QSC degenerates into the [Formula: see text]-system for integrable non-compact Heisenberg spin chain with conformal, [Formula: see text] symmetry. We describe the QSC derivation of Baxter equation and the quantization condition for particular fishnet graphs — wheel graphs, and review numerical and analytic results for them.

Asymmetric shift of exchange bias loop in Ni-Ni(OH)2 core-shell nanoparticles

We report the observation of the asymmetric shift of exchange bias loop in Ni-Ni(OH)2 core-shell nanoparticles where the average size of the ferromagnetic (FM) Ni nanoparticles is ∼30 nm and the thickness of antiferromagnetic (AFM) Ni(OH)2 shell is ∼5 nm. The exchange bias (EB) found below Néel temperature (TN ∼ 22 K) of Ni(OH)2 is path dependent, while the coercivity (HC) increases and decreases for positive and negative bias field respectively. In the present case, we found that the inversion symmetry of hysteresis loop is broken and the shift in EB loop is only observed in descending part of the hysteresis loop, which is conspicuous. We demonstrate that the asymmetric shift of EBs in these core-shell nanoparticles is due to the presence of frustrated super spin glass (SSG) at the interface which influences the reversal mechanism of the hysteresis loop. It is argued that the net interface moment from the SSG at the interface of core-shell nanoparticles sets a unidirectional anisotropy after field cooling, which is thought to be the origin of this path dependency of the EB and observed via descending part of the hysteresis loop, ushering potential for novel spin based applications.

Evaluation of the operatorial Q-system for non-compact super spin chains

We present an approach to evaluate the full operatorial Q-system of all mathfrak{u}left(p,qBig|r+sright) -invariant spin chains with representations of Jordan-Schwinger type. In particular, this includes the super spin chain of planar mathcal{N}=4 super Yang-Mills theory at one loop in the presence of a diagonal twist. Our method is based on the oscillator construction of Q-operators. The Q-operators are built as traces over Lax operators which are degenerate solutions of the Yang-Baxter equation. For non-compact representations these Lax operators may contain multiple infinite sums that conceal the form of the resulting functions. We determine these infinite sums and calculate the matrix elements of the lowest level Q-operators. Transforming the Lax operators corresponding to the Q-operators into a representation involving only finite sums allows us to take the supertrace and to obtain the explicit form of the Q-operators in terms of finite matrices for a given magnon sector. Imposing the functional relations, we then bootstrap the other Q-operators from those of the lowest level. We exemplify this approach for non-compact spin −s spin chains and apply it to mathcal{N}=4 at the one-loop level using the BMN vacuum as an example.

Defect induced magnetism and super spin glass state in reactive ion beam deposited nano-structured AlN thin films

Defect induced magnetism is reported in undoped aluminium nitride thin films deposited using reactive ion beam sputtering of aluminium in nitrogen plasma. The films have been deposited on silicon substrate at different temperatures. Existence of the defects in the films has been verified using room temperature photo-luminescence measurements. Owing to nano-crystalline nature of the films, super-magnetic ground states have been observed. A cross-over from super paramagnetic to super spin glass state has been observed as the grain density increases. Detailed magnetisation measurements along with AC susceptibility measurements have been used to determine the ground states in these AlN thin films.

Grassmannian integral for general gauge invariant off-shell amplitudes in mathcal{N}=4 SYM

In this paper we consider tree-level gauge invariant off-shell amplitudes (Wilson line form factors) in mathcal{N}=4 SYM with arbitrary number of off-shell gluons or equivalently Wilson line operator insertions. We make a conjecture for the Grassmannian integral representation for such objects and verify our conjecture on several examples. It is remarkable that in our formulation one can consider situation when on-shell particles are not present at all, i.e. we have Grassmannian integral representation for purely off-shell object. In addition we show that off-shell amplitude with arbitrary number of off-shell gluons could be also obtained using quantum inverse scattering method for auxiliary mathfrak{g}mathfrak{l}left(4Big|4right) super spin chain.

Wilson lines, Grassmannians and gauge invariant off-shell amplitudes in mathcal{N}=4 SYM

In this paper we consider tree-level gauge invariant off-shell amplitudes (Wilson line form factors) in mathcal{N}=4 SYM. For the off-shell amplitudes with one leg off-shell we present a conjecture for their Grassmannian integral representation in spinor helicity, twistor and momentum twistor parameterizations. The presented conjecture is successfully checked against BCFW results for MHVn, NMHV4 and NMHV5 off-shell amplitudes. We have also verified that our Grassmannian integral representation correctly reproduces soft (on-shell) limit for the off-shell gluon momentum. It is shown that the (deformed) off-shell amplitude expressions could be also obtained using quantum inverse scattering method for auxiliary mathfrak{g}mathfrak{l}left(4Big|4right) super spin chain.

Large exchange bias effect in the super spin glass state of Mn50Ni38Al12 alloy

A large exchange bias field (HEB) of 5.3 kOe which so far, is the largest value found in MnNi-based alloys, was observed in Mn50Ni38Al12 ribbon. DC and AC magnetic measurements show super spin glass (SSG) behavior below 130 K and superparamagnetic behavior above this temperature. Different from other systems, the pinning and pinned phases are both SSG. Due to the high content of Mn and low content of Al there exists considerable disorder in Mn50Ni38Al12 which is responsible for the large HEB.

Magnetic ground state and giant spontaneous exchange bias in Ni46Mn43In11 alloy

We report non-equilibrium dynamics and giant spontaneous exchange bias obtained in zero field cooled mode for Ni46Mn43In11 alloy. The dc magnetic measurements indicate a super spin glass type magnetic ground state in the system. This SSG state is formed when superparamagnetic domains are collectively frozen inside strong antiferromagnetic matrix at low temperature. The ZFCEB arises due to the development of strong superferromagnetic unidirectional anisotropy at the interface of SSG and AFM during the initial magnetization processes. The temperature variation of field cooled exchange bias and ZFCEB is almost similar whilst their field dependency is different. Possible reasons for observed behaviors are comprehensively discussed in this article.