Metamagnetic Transition Research Articles

Functionalized magnetic composite nano/microfibres with highly oriented van der Waals CrI3 inclusions by electrospinning

This study reports on the synthesis of highly oriented chromium triiodide (CrI3) magnetic inclusions inside nano/microfibres with a polyethylene oxide matrix, prepared by the electrospinning technique. The structural, microstructural and spectroscopic analysis shows uniformly dispersed CrI3 nanosized inclusions inside the fibres, presenting a C2/m monoclinic structure at room temperature, where their c-axis is perpendicular to the fibre mat plane and the ab layers are in-plane. Analysis of the magnetic properties show that the samples have a ferromagnetic–paramagnetic phase transition at ∼55–56 K, lower than that of bulk CrI3. Noticeably, a field-driven metamagnetic transition is observed below ∼45 K, from M versus H curves, when the applied magnetic field is perpendicular to the fibre mat plane, while it is strongly reduced when the field is in-plane. This anisotropic behaviour is attributed to the field-induced changes from antiferromagnetic to ferromagnetic interlayer magnetic moment alignment along the CrI3 c-axis stacked layers. These CrI3 electrospun fibres then show an efficient cost-effective route to synthesize magnetic composite fibres with highly oriented van der Walls inclusions, for spintronic applications, taking advantage of their anisotropic 2D layered materials properties.

Anomalous Hall resistivity and possible topological Hall effect in the EuAl4 antiferromagnet

We report the observation of anomalous Hall resistivity in single crystals of EuAl$_4$, a centrosymmetric tetragonal compound, which exhibits coexisting antiferromagnetic (AFM) and charge-density-wave (CDW) orders with onset at $T_\mathrm{N} \sim 15.6$ K and $T_\mathrm{CDW} \sim 140$ K, respectively. In the AFM state, when the magnetic field is applied along the $c$-axis direction, EuAl$_4$ undergoes a series of metamagnetic transitions. Within this field range, we observe a clear hump-like anomaly in the Hall resistivity, representing part of the anomalous Hall resistivity. By considering different scenarios, we conclude that such a hump-like feature is most likely a manifestation of the topological Hall effect, normally occurring in noncentrosymmetric materials known to host nontrivial topological spin textures. In view of this, EuAl$_4$ would represent a rare case where the topological Hall effect not only arises in a centrosymmetric structure, but it also coexists with CDW order.

Unique magnetic properties of Nd based cuprate francisite: Major enhancement upon Co doping

To understand the physical mechanism of intralayer ferromagnetic (FM) and interlayer antiferromagnetic (AFM) interactions in quasi-two-dimensional model of a real three-dimensional system, rare earth (RE)-Nd based cuprate francisite, Cu3Nd(SeO3)2O2Cl (NdCufr) was doped with Co and studied using structural (X-ray diffraction technique), magnetic (temperature and field dependent magnetization and specific heat measurements) and local structural (X-ray absorption technique) techniques supported by first principle theoretical calculation. The structure of the samples is orthorhombic and doped specimens indicate more or less substitutional incorporation of Co at Cu site. The magnetic properties highlighted with two transitions, viz. AFM to paramagnetic (PM) transition around 30 K and a spin reorientation transition (SRT) below 10 K. Two phenomena viz. magnetic hysteresis below SRT and magnetic field induced metamagnetic transition (MMT) were observed. Co doping significantly enhanced these two phenomena in addition to change the transition temperatures. The concomitant change and enhancement of magnetic properties by Co doping has been interpreted using splitting scheme of Cu-d and Nd-f states. The local structure study corroborates the overall findings and detects the cause of unexpected trend of magnetism with increasing Co doping.

Magnetotransport of dirty-limit van Hove singularity quasiparticles

Tuning of electronic density-of-states singularities is a common route to unconventional metal physics. Conceptually, van Hove singularities are realized only in clean two-dimensional systems. Little attention has therefore been given to the disordered (dirty) limit. Here, we provide a magnetotransport study of the dirty metamagnetic system calcium-doped strontium ruthenate. Fermi liquid properties persist across the metamagnetic transition, but with an unusually strong variation of the Kadowaki-Woods ratio. This is revealed by a strong decoupling of inelastic electron scattering and electronic mass inferred from density-of-state probes. We discuss this Fermi liquid behavior in terms of a magnetic field tunable van Hove singularity in the presence of disorder. More generally, we show how dimensionality and disorder control the fate of transport properties across metamagnetic transitions.

Promoting Metamagnetic Transition by Interphase Magnetic Coupling

AbstractMagnetic mixed‐phase materials with competing ground states are important from both scientific and technical points of view due to their magnetic phase transition and phase coexistence properties. Unlike artificially fabricated multi‐phase composites, it should be possible to modify their physical properties more efficiently by making use of the interphase coupling effects in mixed‐phase materials. In this study, the magneto‐transport properties are investigated to provide evidence of the existence of interphase coupling in a magnetic mixed‐phase system, specifically, Ni‐doped FeRh thin films. The rotation of the external magnetic field induces an emergent promotion effect of the antiferromagnetic (AFM)–ferromagnetic (FM) phase transition, which can be attributed to the modification of the magnetic free energy by interphase magnetic coupling across the AFM–FM phase boundary. The results shed light on the availability of an extra degree of freedom for manipulating the physical properties of material systems with mixed magnetic phases and help to further exploit their potential applications.

Оптическая спектроскопия крамерсовских дублетов иона Er-=SUP=-3+-=/SUP=- в двумерном фрустированном магнетике Cu-=SUB=-3-=/SUB=-Er(SeO-=SUB=-3-=/SUB=-)-=SUB=-2-=/SUB=-O-=SUB=-2-=/SUB=-Cl

Francisites Cu3M(YO3)2O2X (M = Bi or rare earth, Y = Se, Te, X = Br, Cl, I) attract grate attention due to their interesting magnetic properties, such as metamagnetic transitions in relatively weak magnetic fields, magnetic phase transitions including spin reorientation, as well as model systems for studying two-dimensional and frustrated magnetism. In this work, a low-temperature optical spectroscopic study is presented of erbium francisite Cu3Er(SeO3)2O2Cl. The observed splittings of the spectral lines corresponding to the f f transitions in the Kramers Er3+ ion unambiguously indicates the magnetic ordering of the crystal at a temperature TN = 37.5 K. The temperature dependence of the splitting of the main doublet of the erbium ion is determined. The contribution of erbium to the heat capacity and magnetic susceptibility of Cu3Er(SeO3)2O2Cl is calculated.

Peculiarity of Magnetocaloric and Magnetoresistance Effects in Ni-Mn-Sn-Fe Alloy with Successive Metamagnetic Sructural Transitions

Peculiarity of Magnetocaloric and Magnetoresistance Effects in Ni-Mn-Sn-Fe Alloy with Successive Metamagnetic Sructural Transitions

Systematic analysis of metamagnetic transitions in A-site disordered Sm0.5(Ca0.5−ySry)MnO3 compounds: A combined experimental and model Hamiltonian study

We investigate the ultra-sharp jump in the isothermal magnetization and the resistivity in the polycrystalline Sm0.5(Ca0.5−ySry)MnO3(y = 0, 0.1, 0.2, 0.25, 0.3, 0.5) compounds. The critical field (Hcr), required for the ultra-sharp jump, decreases with the increase of ‘Sr’ concentration, i.e. with an increase of average A-site ionic radius 〈rA〉. In addition, The magneto-transport data indicate that the phase separation increases with the increase of 〈rA〉, i.e. with ’y’. Moreover, the dependency of Hcr with magnetic field sweep rate reveals that the ultra-sharp jump from antiferromagnetic (AFM) state to the ferromagnetic (FM) state is of martensitic in nature. In parallel with experiments, we have carried out numerical calculations to understand the role of A-site disorder in the metamagnetic transition. Our two-band double exchange model Hamiltonian calculations show that the ‘Sr’ doping induces the ferromagnetic clusters in the antiferromagnetic insulating phase and in turn reduces the critical field. Overall, our combined study comprising of several materials with different composition of A-site reveal the fact that how and why certain A-type disorder produces prominent metamagnetic transition.

Metamagnetic transitions and anomalous magnetoresistance in EuAg4As2 crystals

In this paper, the magnetic and transport properties were systematically studied for EuAg$_4$As$_2$ single crystals, crystallizing in a centrosymmetric trigonal CaCu$_4$P$_2$ type structure. It was confirmed that two magnetic transitions occur at $\textit{T}$$_{N1}$ = 10 K and $\textit{T}$$_{N2}$ = 15 K, respectively. With the increasing field, the two transitions are noticeably driven to lower temperature. At low temperatures, applying a magnetic field in the $\textit{ab}$ plane induces two successive metamagnetic transitions. For both $\textit{H}$ $\parallel$ $\textit{ab}$ and $\textit{H}$ $\parallel$ $\textit{c}$, EuAg$_4$As$_2$ shows a positive, unexpected large magnetoresistance (up to 202\%) at low fields below 10 K, and a large negative magnetoresistance (up to -78\%) at high fields/intermediate temperatures. Such anomalous field dependence of magnetoresistance may have potential application in the future magnetic sensors. Finally, the magnetic phase diagrams of EuAg$_{4}$As$_{2}$ were constructed for both $\textit{H}$ $\parallel$ $\textit{ab}$ and $\textit{H}$ $\parallel$ $\textit{c}$.

Table-like magnetocaloric effect and large refrigerant capacity in Nd6Fe13Pd1-xAgx compounds

Table-like magnetocaloric effect is significant for using the Ericsson cycle in the applications of magnetic refrigeration above 20 K. A series of Nd6Fe13Pd1-xAgx (x = 0.1, 0.2, 0.3, 0.4) compounds were prepared by the arc-melting method, showing a single crystalline phase in the tetragonal Nd6Fe13Si-type structure with the space group I4/mcm. All of the compounds undergo a first-order magnetic transition from the ferromagnetism to antiferromagnetism with the temperature increases, as well as a metamagnetic transition from antiferromagnetic state to ferromagnetic state induced by an applied field. The table-like magnetocaloric effects with large refrigerant capacities in these compounds have been observed, which is very rare in a single phase. A constant ΔSM in a temperature span of 60 K in the Nd6Fe13Pd0.6Ag0.4 compound can be observed. For a field change of 0–5 T, the peak values of |ΔSM| for the Nd6Fe13Pd0.9Ag0.1, Nd6Fe13Pd0.8Ag0.2, Nd6Fe13Pd0.7Ag0.3 and Nd6Fe13Pd0.6Ag0.4 compounds are estimated to be 4.9 J kg−1 K−1, 4.5 J kg−1 K−1, 3.5 J kg−1 K−1 and 3.4 J kg−1 K−1 with the corresponding refrigerant capacity values of 327 J kg−1, 315 J kg−1, 306 J kg−1 and 289 J kg−1, respectively. The table-like magnetocaloric effect and large working temperature spans make the series of compounds a good candidate for single-phase magnetic refrigeration material at low temperature based on the Ericsson cycle.

Influence of metamagnetic phase transitions on thermodynamics of frustrated systems with octahedral structure

Common effects of the geometric frustration and of the metamagnetic phase transitions on the thermodynamic properties of antiferromagnetic systems with the octahedral structure are investigated using an exactly solvable antiferromagnetic model on the octahedral recursive lattice. The residual entropies of all ground states are determined and the existence of two highly macroscopically generated single-point ground states with nonzero residual entropies is shown. The first-order character of the metamagnetic phase transitions of the model is demonstrated by discontinuous behavior of the entropy. The presence of the anomalous Schottky-type behavior of the specific heat capacity, i.e., the appearance of an additional peak in the low-temperature behavior of the specific heat capacity, in the vicinity of the magnetic field values, for which the highly macroscopically degenerated ground states are formed, is demonstrated and discussed. It is shown that the geometric frustration of the model together with the presence of the metamagnetic phase transitions can lead to more complicated behavior of the specific heat capacity, e.g., they have impact on the number of peaks (local maxima) in its behavior. It is also shown that the magnetocaloric effects related to the metamagnetic phase transitions are much more pronounced than those related to the frustration.

Investigation of the itinerant metamagnetic system Hf0.75Ta0.25Fe2 under extreme conditions of pressure or magnetic field

The magnetic and structural properties of Hf0.75Ta0.25Fe2 have been investigated under the duplicate conditions, i.e., high magnetic fields and high pressures, by combining magnetization measurements up to 26 T, neutron powder diffraction experiments up to 14.5 T, and angle dispersive synchrotron x-ray diffraction up to 10 GPa. The intermetallic compound Hf0.75Ta0.25Fe2 exhibits an antiferromagnetic (AFM) ground state below the Néel temperature TN = 342 K. In the AFM structure, the Fe-6h magnetic moments (1.02 μΒ at 2 K) align along the c axis while Fe atoms at 2a sites are not magnetically ordered. We further show that the AFM ground state gets transformed into a ferromagnetic (FM) state via a field-induced metamagnetic phase transition. Magnetic-field dependent neutron diffractograms demonstrate that FM phase sets in with a change of the easy magnetization direction from axial to basal-plane and an extremely anisotropic lattice expansion. The unit cell expands drastically in the basal plane upon increasing the applied magnetic field, while its dimension along c-axis shrinks slightly; resulting in a huge positive volume magnetostriction ΔV/V = 0.78%. The application of hydrostatic pressure leads to the continuous decrease of the cell parameters. The shrinkage of the hexagonal cell is anisotropic with a larger compression along the six-fold symmetry axis c. A bulk modulus of K0 = 247 GPa has been deduced from the pressure-volume relationship.

Enhanced magnetocaloric effects in hetero-structural alloyed Er2In1-xAlx (0 ≤ x ≤ 0.4) system by novel nonhysteretic metamagnetsm

By hetero-structural alloying antiferromagnetic orthorhombic Er2Al and ferromagnetic hexagonal Er2In which both undergo the second-order phase transition, an unconventional nonhysteretic metamagnetic phase transition is observed at the critical composition of x = 0.2 in Er2In1-xAlx (0 ≤ x ≤ 0.4) system. The magnetic entropy change and adiabatic temperature change is enhanced to 16.9 Jkg−1K−1 and 7.2 K in Er2In0.8Al0.2 with the largest saturation magnetostriction of -1117 ppm under 7 T. By correlating with specific heat and magnetotransport measurement, the origin of such unique nonhysteretic metamagnetism is assumed to be from the field-induced reconstruction of 5d subband of rare-earth elements.

Magnetic properties of a pseudo-one-dimensional ferrimagnetic semiconductor Eu3Sb4Se9

The resistivity, anisotropic magnetic properties, and magnetic critical behavior of single-crystalline Eu3Sb4Se9 with a pseudo-one-dimensional structure have been studied. The resistivity shows a semiconducting temperature dependence, which gives a bandgap of 0.65 eV. The samples are paramagnetic and isotropic at high temperatures and undergo a transition at Tc = 5.1 K into a ferrimagnetic phase. The long crystal dimension, the crystalline b axis, is the easy axis. Below Tc, the samples have a further metamagnetic transition from the ferrimagnetic to ferromagnetic state when the field is along the easy axis. The low-field magnetization around Tc cannot be described by the mean-field theory for a second-order phase transition, but can be well fitted by the modified Arrott plot, which gives a set of critical exponents β = 0.82, γ = 1.08, and δ = 2.35. The magnetic phase diagram for the field applied parallel to the easy axis is finally established.

Sputter-engineering a first-order magnetic phase transition in sub-15-nm-thick single-crystal FeRh films

Equiatomic FeRh alloys undergo a fascinating first-order metamagnetic phase transition (FOMPT) just above room temperature, which has attracted reinvigorated interest for applications in spintronics. Until now, all attempts to grow nanothin FeRh alloy films have consistently shown that FeRh layers tend to grow in the Volmer-Weber growth mode. Here we show that sputter-grown sub-15-nm-thick FeRh alloy films deposited at low sputter-gas pressure, typically $\ensuremath{\sim}0.1$ Pa, onto (001)-oriented MgO substrates, grow in a peening-induced Frank-van der Merwe growth mode for FeRh film thicknesses above 5 nm, circumventing this major drawback. The bombardment of high-energy sputtered atoms, the atom-peening effect, induces a rebalancing between adsorbate-surface and adsorbate-adsorbate interactions, leading to the formation of a smooth continuous nanothin FeRh film. Chemical order in the films increases with the FeRh thickness, ${t}_{\text{FeRh}}$, and varies monotonically from 0.75 up to 0.9. Specular x-ray diffraction scans around Bragg peaks show Pendell\"osung fringes for films with ${t}_{\text{FeRh}}\ensuremath{\ge}5.2$ nm, which reflects in smooth well-ordered densified single-crystal FeRh layers. The nanothin film's roughness varies from 0.6 down to about 0.1 nm as ${t}_{\text{FeRh}}$ increases, and scales linearly with the integral breadth of the rocking curve, proving its microstructured origin. Magnetometry shows that the FOMPT in the nanothin films is qualitatively similar to that of the bulk alloy, except for the thinnest film of 3.7 nm.

Lifshitz transition underlying the metamagnetic transition of UPt3

Comparing quantum oscillation measurements, dc magnetoresistance measurements, and Fermi surfaces obtained from LDA calculations, we argue that the metamagnetic transition of UPt3, which occurs at an applied field μ ◦ H M ∼ 20 T, coincides with a Lifshitz transition at which an open orbit on the band 2 hole-like Fermi surface becomes closed for one spin direction. At low field, proximity of the Fermi energy to this particular van Hove singularity may have implications for the superconducting pairing potential of UPt3. In our picture the magnetization comes from non-linear spin-splitting of the heavy fermion bands. In support of this, we show that the non-linear field dependence of a particular quantum oscillation frequency can be fitted by assuming that the corresponding extremal Fermi surface area is proportional to the magnetization. In addition, below H M , we find in our LDA calculations a new, non-central orbit on band 1, whose non-linear behaviour explains a field-dependent frequency recently observed in magnetoacoustic quantum oscillation measurements.

Direct-Write of Nanoscale Domains with Tunable Metamagnetic Order in FeRh Thin Films.

We have directly written nanoscale patterns of magnetic ordering in FeRh films using focused helium-ion beam irradiation. By varying the dose, we pattern arrays with metamagnetic transition temperatures that range from the as-grown film temperature to below room temperature. We employ transmission electron microscopy, X-ray diffraction, and temperature-dependent transport measurements to characterize the as-grown film, and magneto-optic Kerr effect imaging to quantify the He+ irradiation-induced changes to the magnetic order. Moreover, we demonstrate temperature-dependent optical microscopy and conductive atomic force microscopy as indirect probes of the metamagnetic transition that are sensitive to the differences in dielectric properties and electrical conductivity, respectively, of FeRh in the antiferromagnetic (AF) and ferromagnetic (FM) states. Using density functional theory, we quantify strain- and defect-induced changes in spin-flip energy to understand their influence on the metamagnetic transition temperature. This work holds promise for in-plane AF-FM spintronic devices, by reducing the need for multiple patterning steps or different materials, and potentially eliminating interfacial polarization losses due to cross material interfacial spin scattering.

Magnetic field induced reconstruction of electronic structure in Sr3Ru2O7 nanosheets

The origin of the large magnetoresistance (MR) peak induced by the metamagnetic transition (MMT) in ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ has attracted extensive attention, but still remains puzzling. Here we performed systematic magnetotransport and torque magnetometry measurements of ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ nanosheets, and found surprisingly that the MR peak, together with the MMT, shifts dramatically toward low magnetic field with the decrease of thickness. Meanwhile, the Hall coefficient shows clearly a sign change near the MR peak position, indicating a magnetic field induced change of band topology. Combined with the theoretical calculation, we argue that the nature of the MR peak in ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ is associated with the so-called Lifshitz transition due to van Hove singularity, which is closer to the Fermi level in thinner nanosheets.

Mn1/4NbS2 : Magnetic and magnetotransport properties at ambient pressure and ferro- to antiferromagnetic transition under pressure

Transition-metal dichalcogenides (TMDCs) stand out with their high chemical stability and the possibility to incorporate a wide range of atoms and molecules between the layers. The behavior of conduction electrons in such $3d$-metal-inserted materials is closely related to their magnetic properties and can be sensitively controlled by external magnetic fields. Here, we study the magnetotransport properties of Mn-inserted $\mathrm{Nb}{\mathrm{S}}_{2}, {\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_{2}$, demonstrating a complex behavior of the magnetoresistance and of the ordinary and anomalous Hall resistivity. Application of high pressure as tuning parameter leads to the drastic changes of the magnetotransport properties of ${\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_{2}$ exhibiting large negative magnetoresistance up to $\ensuremath{-}65%$ at 7.1 GPa. First-principles electronic structure calculations indicate a pressure-induced transition from a ferromagnetic to antiferromagnetic state. Theoretical calculations accounting for the finite temperature magnetic properties suggest a field-induced metamagnetic ferromagnetic-antiferromagnetic transition as an origin of the large negative magnetoresistance. These results inspire the development of materials for spintronic applications based on $3d$-element-inserted TMDCs with a well controllable metamagnetic transition.

The Impact of Disorder on the Disappearance of Metamagnetic Behavior and Enhancement of Temperature Coefficient of Resistivity for (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 Ceramics

The polycrystalline samples (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 were prepared by the solid-state reaction method. Magnetization measurements versus temperature were performed in order to investigate the magnetic properties such as the metamagnetic transition. The transition temperature estimated from the maximum of dM/dH is found sensitive to disorder σ2 leading to the formation of an inhomogeneous metastable state and to subsequent magnetization jumps. The peak temperature coefficient of the resistivity improved significantly from 1.54 to 8.21% K−1 due to the increase in disorder. These findings suggest that (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 ceramics can be used to prepare uncooled infrared bolometers.