High quality epitaxial niobium nitride (NbN) thin films were grown on MgO (001) substrates by pulsed laser deposition (PLD) from a pure NbN target while varying the nitrogen partial pressure inside the chamber. This variation provides an additional degree of freedom in the film formation: by adjusting the nitrogen partial pressure, we modify the lattice parameter of the delta-NbN phase systematically, and tune the superconducting transition temperature ( TC). X-ray Diffraction and Hall conductivity measurements show that this change in TC arises from the combined influence of lattice strain, and carrier concentration. A phenomenological analysis based on the McMillan and Allen Dynes strong coupling models closely captures the observed trends. Our results demonstrate that rational design of epitaxial superconducting materials, essential for interface control of physical properties, can be achieved by tuning the lattice parameter and carrier concentration in delta-NbN. Furthermore, our results provide a pathway to separate intrinsic structural factors affecting the transition temperature from proximity-induced effects in superconducting hybrid structures.

Unconventional magnetic materials including non-collinear antiferromagnets, p-wave magnets and altermagnets, are an emerging frontier for quantum spintronics and hybrid quantum devices. Critical to the application of these materials is control over the magnetic domain state, as their unique, symmetry-driven properties vanish in a multi-domain limit. However, the mechanisms governing domain formation in materials with compensated local moments remain poorly understood. In this work, we examine the ferrimagnetic to non-collinear antiferromagnetic phase transition of Mn3NiN using scanning nitrogen-vacancy centre magnetometry. We provide nanoscale mapping of the magnetic domain evolution on cooling and correlate the local stray fields with global magnetometry and anomalous Hall effect measurements. We observe the formation of a disordered, dendritic domain structure whose roughness is quantified using its fractal dimension. The fractal dimension steadily increases on cooling through the transition, saturating at a value of ~ 1.55 in the non-collinear phase, but the domain area distribution does not show any significant changes. We show this behaviour cannot be explained by the balance of demagnetisation energy and domain wall energy, and conclude elastic contributions and defects are a critical factor to explain the domain size.

La(Fe,Si)13-based alloys, with giant magnetocaloric effect, still encounter significant degradation issues prior to commercial viability. In this work, the corrosion behavior of ferro magnetic La(Fe,Si)13Hy was investigated with electrochemical linear polarization resistance measurements under conditions with zero, 1T parallel and perpendicular magnetic fields, mimicking practical application scenarios. The results demonstrated that both parallel and perpendicular magnetic fields had a suppressive effect on corrosion rates due to the combined influence of magnetohydrodynamic forces and magnetic field gradient forces. The inhibiting efficiency of the parallel field decreased with increasing exposure period, while that of the perpendicular field continued to increase over time. The magnetic field also affected the relative proportion of rust phases, and thereby the protectiveness of the rust layer. This highlights the importance of conducting experiments under service conditions to understand the degradation mechanisms of magnetic cooling devices.

Noncollinear antiferromagnets offer much promise for antiferromagnetic spintronics and neuromorphic applications with a plethora of functional properties surpassing many competing magnetic systems. Films grown on mismatched substrates may relieve strain by the creation of slip-plane defects that strongly manipulate global physical properties important for application. This work demonstrates that a post growth annealing strategy results in near-defect-free, structurally robust films that reveal the underlying thermal evolution of the magnetic order symmetry. Beyond a critical film thickness, the spin structure transitions between two right-handed irreducible chiral representations via left-handed chiral ordering producing a striking change in the sign and angular dependence of the Anomalous Hall coefficient. The previously established mechanism of spin rotations in the (111) plane cannot fully explain the transition in applied magnetic field, and using a macrospin model this work finds that rotations along the chirality-inverting [1-10] direction are energetically preferable under certain conditions. These observations suggest that both left-handed and right-handed chiral order can be accessed in a single system, opening new routes to engineer devices by controlled switching of magnetic chirality allowing selection of associated functional properties as governed by symmetry.

The durability of La(Fe, Si)13-based magnetocaloric alloys in magnetic cooling devices present challenges mainly due to the material's susceptibility to corrosion in water-related heat transfer fluids. This study proposes an electrophoretic deposition method to deposit graphene oxide coatings on LaFe13.9Si1.4 thin plates under various applied voltages. The results show that the coating prepared at 5 V significantly enhanced corrosion resistance, achieving an inhibition efficiency of 36 %. Additionally, the LaFe13.9Si1.4-GO sample exhibited no reduction in the maximum magnetic entropy change. This study demonstrates that graphene oxide coatings can serve as effective corrosion-resistant coatings for La-Fe-Si magnetocaloric alloys, offering guidance to ensure the integrity of magnetic cooling devices over long term.

In 1966, Pierre-Gilles de Gennes proposed a non-volatile mechanism for switching superconductivity on and off in a magnetic device. This involved a superconductor (S) sandwiched between ferromagnetic (F) insulators in which the net magnetic exchange field could be controlled through the magnetisation-orientation of the F layers. Because superconducting switches are attractive for a range of applications, extensive studies have been carried out on $F/S/F$ structures. Although these have demonstrated a sensitivity of the superconducting critical temperature ($T_{c}$) to parallel (P) and antiparallel (AP) magnetisation-orientations of the F layers, corresponding shifts in $T_c$ (i.e., ${\Delta}T_c = T_{c,AP} - T_{c,P}$) are lower than predicted with ${\Delta}T_c$ only a small fraction of $T_{c,AP}$, precluding the development of applications. Here, we report $EuS/Au/Nb/EuS$ structures where EuS is an insulating ferromagnet, Nb is a superconductor and Au is a heavy metal. For P magnetisations, the superconducting state in this structure is quenched down to the lowest measured temperature of 20 mK meaning that ${\Delta}T_c/T_{c,AP}$ is practically 1. The key to this so-called absolute switching effect is a sizable spin-mixing conductance at the $EuS/Au$ interface which ensures a robust magnetic proximity effect, unlocking the potential of $F/S/F$ switches for low power electronics.

Antiferromagnets hosting structural or magnetic order that breaks time reversal symmetry are of increasing interest for “beyond von Neumann” computing applications because the topology of their band structure allows for intrinsic physical properties, exploitable in integrated memory and logic function. One such group are the noncollinear antiferromagnets. Essential for domain manipulation is the existence of small net moments found routinely when the material is synthesized in thin film form and attributed to symmetry breaking caused by spin canting, either from the Dzyaloshinskii–Moriya interaction or from strain. Although the spin arrangement of these materials makes them highly sensitive to strain, there is little understanding about the influence of local strain fields caused by lattice defects on global properties, such as magnetization and anomalous Hall effect. This premise is investigated by examining noncollinear antiferromagnetic films that are either highly lattice mismatched or closely matched to their substrate. In either case, edge dislocation networks are generated and for the former case, these extend throughout the entire film thickness, creating large local strain fields. These strain fields allow for finite intrinsic magnetization in seemingly structurally relaxed films and influence the antiferromagnetic domain state and the intrinsic anomalous Hall effect.

The NaZn13 type itinerant magnet LaFe13-xSix has seen considerable interest due to its unique combination of large magnetocaloric effect and low hysteresis. Here we demonstrate, with a combination of magnetometry, bespoke microcalorimetry and inelastic neutron scattering that this is due to the presence of paramagnetic spin fluctuations, which build up as the critical point is approached. While thermal measurements show significant latent heat independent changes in the heat capacity, inelastic neutron scattering reveals the presence of broad quasielastic scattering that persists above Tc, in addition to a finite Q quasielastic peak at Q=0.52 A^-1 (close to a 100 Bragg reflection in this system at Q = 0.54 A^-1). This finite Q quasielastic peak appears only in the paramagnetic state and when in proximity to the itinerant metamagnetic transition. We associate these observations with a hidden competing phase and spin fluctuations close to the transition temperature and magnetic field, that persist across the magnetic transition.

Heusler alloys are widely studied due to their potential for practical applications, making use of their martensitic transformations. However, hysteresis is a long-standing drawback that reduces the chance of transferring these alloys from the laboratory to industry. In this work, we studied a Cr-doped Ni2MnGa-based material designed by integrating data obtained from the previous phase and hysteresis diagrams taken from the literature, reaching Ni2.15Mn0.70Cr0.15Ga. The compound presents a magnetostructural transition at room temperature, with a ferromagnetic martensite phase, and moderate thermal hysteresis of approximately 4 K. The magnetocaloric effect was explored, showing a reversible entropy change higher than 8 Jkg- 1K(-1) under 0-5 T field change, an advance towards high reversibility for this family alloys.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to "Giant Piezomagnetism in Mn3NiN"David Boldrin*David BoldrinMore by David Boldrinhttps://orcid.org/0000-0003-3833-8341, Andrei P. MihaiAndrei P. MihaiMore by Andrei P. Mihaihttps://orcid.org/0000-0002-7204-9087, Bin ZouBin ZouMore by Bin Zou, Jan ZemenJan ZemenMore by Jan Zemen, Ryan ThompsonRyan ThompsonMore by Ryan Thompson, Ecaterina WareEcaterina WareMore by Ecaterina Ware, Bogdan V. NeamtuBogdan V. NeamtuMore by Bogdan V. Neamtu, Luis GhivelderLuis GhivelderMore by Luis Ghivelderhttps://orcid.org/0000-0002-5667-6531, Bryan EsserBryan EsserMore by Bryan Esser, David W. McCombDavid W. McCombMore by David W. McComb, Peter PetrovPeter PetrovMore by Peter Petrovhttps://orcid.org/0000-0003-3643-6685, and Lesley F. CohenLesley F. CohenMore by Lesley F. CohenCite this: ACS Appl. Mater. Interfaces 2024, 16, 2, 2997Publication Date (Web):January 6, 2024Publication History Received5 December 2023Published online6 January 2024Published inissue 17 January 2024https://pubs.acs.org/doi/10.1021/acsami.3c16464https://doi.org/10.1021/acsami.3c16464correctionACS PublicationsCopyright © 2024 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views345Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (1 MB) Get e-Alertsclose Get e-Alerts

The observation of a sizable anomalous Hall effect in magnetic materials with vanishing magnetization has renewed interest in understanding and engineering this phenomenon. Antiferromagnetic antiperovskites are one of emerging material classes that exhibit a variety of interesting properties owing to a complex electronic band structure and magnetic ordering. Reports on the anomalous Nernst effect and its magnitude in this class of materials are, however, very limited. This scarcity may be partly due to the experimental difficulty of reliably quantifying the anomalous Nernst coefficient. Here, we report experiments on the anomalous Nernst effect in antiferromagnetic antiperovskite Mn$_3$NiN thin films. Measurement of both the anomalous Hall and Nernst effects using the same sample and measurement geometry makes it possible to directly compare these two effects and quantify the anomalous Nernst coefficient and conductivity in Mn$_3$NiN. We carefully evaluate the spatial distribution of the thermal gradient in the sample and use finite element modeling to corroborate our experimental results.

The magnetically frustrated manganese nitride antiperovskite family displays significant changes of entropy under changes in hydrostatic pressure near a first-order antiferromagnetic to paramagnetic phase transition that can be useful for the emerging field of solid-state barocaloric cooling. In previous studies, the transition hysteresis has significantly reduced the reversible barocaloric effects (BCE). Here we show that the transition hysteresis can be tailored through quaternary alloying in the Mn _3 Cu $_{1-x}$ Sn $_{x}$ N system. We find the magnitude of hysteresis is minimised when Cu and Sn are equiatomic ( x = 0.5) reaching values far less than previously found for Mn _3 A N ( $A = $ Pd, Ni, Ga, Zn), whilst retaining entropy changes of the same order of magnitude. These results demonstrate that reversible BCE are achievable for p < 100 MPa in the Mn _3 ( A , B )N family and suggest routes to modify the transition properties in compounds of the same family.

Ni-Mn-Ga based alloys are widely studied due to their potential for practical applications, making use of their martensitic transformations. However, hysteresis is a long-standing drawback that reduces the chance of transferring these alloys from the laboratory to industry. In this work, we studied a Cr-doped Ni2.15Mn0.70Cr0.15Ga alloy. We arrived at this composition by integrating data obtained from the previous phase and hysteresis diagrams taken from the literature. The compound presents a magnetostructural transition at room temperature, with a ferromagnetic martensite phase, and moderate thermal hysteresis of approximately 4 K. The magnetocaloric and ferromagnetic shape memory effects were explored, showing a reversible entropy change of approximately 9 Jkg-1K-1 under 0-5 T field change, and a cyclical magnetic -field-induced deformation close to 0.81% under 0-9 T, an advance towards high reversibility for this family alloys.(c) 2022 Elsevier B.V. All rights reserved.

Proximity-induced long-range spin-triplet supercurrents, important for the field of superconducting spintronics, are generated in superconducting/ferromagnetic heterostructures when interfacial magnetic inhomogeneities responsible for spin mixing and spin flip scattering are present. The multilayer stack Nb/Cr/Fe/Cr/Nb has been shown to support such currents when fabricated into Josephson junction devices. However, creating pure spin currents controllably in superconductors outside of the Josephson junction architecture is a bottleneck to progress. Recently, ferromagnetic resonance was proposed as a possible direction, the signature of pure supercurrent creation being an enhancement of the Gilbert damping below the superconducting critical temperature, but the necessary conditions are still poorly established. Here, we demonstrate that pumping pure spin currents into a superconductor in the presence of an external magnetic field is only possible when conditions supporting proximity-induced spin-triplet effects are satisfied. Our study is an important step forward for pure spin supercurrent creation, considerably advancing the field of superconducting spintronics.

The magnetocaloric effect is often largest within the neighborhood of a first-order phase transition. This effect can be utilized in magnetocaloric refrigeration, which completely eliminates the need for the greenhouse gases utilized in conventional refrigeration. However, such transitions present unique dynamical effects and are accompanied by hysteresis, which can be detrimental for such refrigeration applications. In this work, a Landau theory-based relaxational model is used to study the magnetic hysteresis and dynamics of the first-order magnetic transition of LaFe 13− x Si x . Fitting the experimental magnetization data as a function of applied magnetic field under different field sweep rates with this model provided the Landau parameters ( A, B , and C ) and the kinetic coefficient of the studied material. We demonstrate the tendency of the magnetic hysteresis to increase with the magnetic field sweep rate, underlining the importance of studying and minimizing the magnetic hysteresis in magnetic refrigerants at practical field sweep rates. While evaluating the temperature dependence of the time required for a complete transition to occur, a nonmonotonic behavior and a sharp peak were found for temperatures near the transition temperature. Such peaks occur at the same temperature as the peak of the magnetic entropy change for low fields, whereas for higher fields the two peaks decouple. This information is critical for technological applications (such as refrigerators/heat pumps) as it provides guidelines for the optimization of the magnetic field amplitude in order to reduce the transition timescale and consequently maximize the machine operational frequency and amount of heat that is pumped in/out per second.

Understanding metal-semiconductor interfaces is critical to the advancement of photocatalysis and sub-bandgap solar energy harvesting where sub-bandgap photons can be excited and extracted into the semiconductor. In this work, we compare the electron extraction efficiency across Au/TiO2 and titanium oxynitride/TiO2-x interfaces, where in the latter case the spontaneously forming oxide layer (TiO2-x) creates a metal-semiconductor contact. Time-resolved pump-probe spectroscopy is used to study the electron recombination rates in both cases. Unlike the nanosecond recombination lifetimes in Au/TiO2, we find a bottleneck in the electron relaxation in the TiON system, which we explain using a trap-mediated recombination model. Using this model, we investigate the tunability of the relaxation dynamics with oxygen content in the parent film. The optimized film (TiO0.5N0.5) exhibits the highest carrier extraction efficiency, slowest trapping and an appreciable hot electron population reaching the surface oxide. Our results demonstrate the productive role oxygen can play in enhancing electron harvesting and elongating electron lifetimes providing an optimized metal-semiconductor interface using only the native oxide of titanium oxynitride.

Here we present a magnetic thin film with a weak ferrimagnetic (FIM) phase above the N\'eel temperature ($T_{N}$ = 240 K) and a non-collinear antiferromagnetic (AFM) phase below, exhibiting a small net magnetisation due to strain-associated canting of the magnetic moments. A long-range ordered FIM phase has been predicted in related materials, but without symmetry analysis. We now perform this analysis and use it to calculate the MOKE spectra in AFM and FIM phases. From the good agreement between the form of the measured and predicted MOKE spectra, we propose the AFM and FIM phases share the magnetic space group C2'/m' and that the symmetry driven magneto-optic and magneto-transport properties are maximised at room temperature in the FIM phase due to the non-zero intrinsic Berry phase contribution present in these materials. A room temperature FIM phase with large optical and transport signatures, as well as sensitivity to lattice strain and magnetic field, has useful prospects for high-speed spintronic applications.