Field-induced Transition Research Articles

Transformation of magnetic ordering in MnCo1-xNixGe (x = 0–0.6) alloys, its investigations on structural, transport, magnetic, and magnetocaloric properties

In the latest study, physical behaviour of (structure, transport, magnetism, and magnetocaloric effect, critical exponents studies) MnCo1-xNixGe (x = 0, 0.2, 0.4, 0.6) intermetallic alloys are enquired. The parental MnCoGe reveals doublet-orthorhombic at ambient temperature, while doping up Ni crystallographic structure is renovated from the mixed-phase of Orthorhombic-Hexagonal to complete hexagonally crystallized by confirmation of high-temperature XRD. From the transport measurements, Semiconductor (x = 0.2) to metallic (x = 0.4, 0.6) transitions are appeared. The suppression of magneto-structural transitions (MST’s), First [(AFM-FM)-(TM)] to Second [(FM-PM)-(TCA)] order transformation are recognized from thermo-magnetic measurements [M (T)]. The presence and absence of Field-Induced Meta Magnetic Transitions (FIMMT) for parent (x = 0) and doped (x = 0.2, 0.4, 0.6) samples have appeared from isothermal magnetization curves [M (H)]. Giant MCE is perceived near RT (303 K) for x = 0 and decreases for Ni-doped samples by dropping temperatures. The change in magnetic entropy (ΔSM) decreases with increasing Ni substitution. Refrigeration capacity (RC) linearly increases with magnetic field for all samples and decreases with Ni compositions.

Magnetostructural features of phase transitions in the Mn-=SUB=-1-x-=/SUB=-Co-=SUB=-x-=/SUB=-NiGe system Part 1. Experimental results

Experimental studies of the magnetic and structural properties of solid solutions of the Mn1-xCoxNiGe system in a wide range of Co concentrations (0.05≤ x≤ 0.8), temperatures (5 K≤ x≤600 K) and magnetic fields (0.016 T≤ x≤ 13.5 T) have revealed a number of nontrivial magnetic and magnetocaloric features of this system. The latter include: 1) a change in the nature of magnetic phase transitions from magnetostructural transitions of the 1st order paramagnetism-antiferromagnetism (0.05≤ x≤ 0.15) to isostructural transitions of the 2nd order paramagnetism-ferromagnetism (0.15≤ x≤0.8) with a change in the concentration of Co ; 2) anomalous behavior of low-temperature regions of magnetization in weak magnetic fields; 3) a change in the saturation magnetization and the appearance of irreversible magnetic field-induced transitions at helium temperatures in strong magnetic fields. Keywords: irreversible magnetostructural first-order phase transition, helimagnetism, direct and inverse magnetocaloric effects.

Magnetic reshuffling and feedback on superconductivity in UTe2 under pressure

The discovery of superconductivity in the heavy-fermion paramagnet ${\mathrm{UTe}}_{2}$ has attracted a lot of attention, particularly due to the reinforcement of superconductivity near pressure- and magnetic-field-induced magnetic quantum phase transitions. A challenge is now to characterize the effects of combined pressure and magnetic fields applied along variable directions in this strongly anisotropic paramagnet. Here, we present an investigation of the electrical resistivity of ${\mathrm{UTe}}_{2}$ under pressure up to 3 GPa and pulsed magnetic fields up to 58 T along the hard magnetic crystallographic directions $\mathbf{b}$ and $\mathbf{c}$. We construct three-dimensional phase diagrams and show that, near the critical pressure, a field-enhancement of superconductivity coincides with a boost of the effective mass related to the collapse of metamagnetic and critical fields at the boundaries of the correlated paramagnetic regime and magnetically-ordered phase, respectively. Beyond the critical pressure, field-induced transitions precede the destruction of the magnetically-ordered phase, suggesting an antiferromagnetic nature. By bringing new elements about the interplay between magnetism and superconductivity, our paper appeals for microscopic theories describing the anisotropic properties of ${\mathrm{UTe}}_{2}$ under pressure and magnetic field.

Hf1–xZrxO2/ZrO2 Nanolaminate Thin Films as a High-κ Dielectric

Engineering of HfO2–ZrO2 ferroelectric thin films can substantially increase their dielectric constant. Here, we investigate dielectric and structural properties of ∼10 nm thin films consisting of stacked 1 nm thin ferroelectric (FE) Hf1–xZrxO2 (HZO(x)) and antiferroelectric (AFE) ZrO2 layers. At x < 0.5, the measurements of polarization vs electric field revealed pure FE hysteresis loops, whereas at x > 0.5, pinched hysteresis loops with some remnant polarization were observed, which indicate a coexistence of FE and AFE orderings. Finally, a pure ZrO2 thin film (x = 1) exhibits only an AFE double hysteresis loop. In this way, we demonstrate that the coexistence of FE and AFE orderings can be controlled by adjusting the composition of HZO(x) layers in the HZO(x)/ZrO2 nanolaminate films. At x = 0.5, the dielectric constant is ∼60 in nanolaminate films, which is much higher than that of the conventional HZO(x) solid solution thin films. Structural investigations confirm a coexistence of polar orthorhombic and nonpolar tetragonal structures, which is consistent with the observed polarization hysteresis loops. We also show that the strain generated in the nanolaminate structure significantly facilitates a field-induced transition from the AFE to the FE phase. The design does not considerably affect the leakage current in HZO(x)/ZrO2 nanolaminate films, which makes this system highly promising for complementary metal oxide semiconductor-compatible capacitors.

Dzyaloshinskii-Moriya anisotropy effect on field-induced magnon condensation in the kagome antiferromagnet α−Cu3.26Mg0.74(OH)6Br2

We performed a comprehensive electron spin resonance, magnetization and heat capacity study on the field-induced magnetic phase transitions in the kagome antiferromagnet $\alpha-Cu_3Mg(OH)_6Br_2$. With the successful preparation of single crystals, we mapped out the magnetic phase diagrams under the $c$-axis and $ab$-plane directional magnetic fields $B$. For $B\|c$, the three-dimensional (3D) magnon Bose-Einstein condensation (BEC) is evidenced by the power law scaling of the transition temperature, $T_c\propto (B_c-B)^{2/3}$. For $B\|ab$, the transition from the canted antiferromagetic (CAFM) state to the fully polarized (FP) state is a crossover rather than phase transition, and the characteristic temperature has a significant deviation from the 3D BEC scaling. The different behaviors of the field-induced magnetic transitions for $B\|c$ and $B\|ab$ could result from the Dzyaloshinkii-Moriya (DM) interaction with the DM vector along the $c$-axis, which preserves the $c$-axis directional spin rotation symmetry and breaks the spin rotation symmetry when $B\|ab$. The 3D magnon BEC scaling for $B\|c$ is immune to the off-stoichiometric disorder in our sample $\alpha-Cu_{3.26}Mg_{0.74}(OH)_6Br_2$. Our findings have the potential to shed light on the investigations of the magnetic anisotropy and disorder effects on the field-induced magnon BEC in the quantum antiferromagnet.

Magnetization reversal, field-induced transitions and H–T phase diagram of Y1−x Ce x CrO3

We report a systematic study of the magnetic phase diagram in the H–T plane, negative magnetization (NM), exchange interactions and field-induced spin–flop transitions in the distorted perovskite Y1−x Ce x CrO3. Locked AFM and weak-FM configurations in Γ4(G z , F y , A x ) phase of YCrO3 (S = 3/2 ground state) unlocks into the Γ2 (F z , G y , C x ; ) phase of the canted AFM and FM structures with the dilute substitution of Ce (x ⩾ 0.05). The asymmetric and symmetric exchange interaction (J AS ∼ 0.11 meV and J S ∼ 0.85 meV) between the trivalent Ce and Cr enable the positive quartic-anisotropy field ( ∼ 2.85 × 102 Oe) along with the second order anisotropy field ( ∼ 5.93 × 102 Oe). Unlike the pristine YCrO3 compound, the Ce incorporated system exhibits a giant fourth-order anisotropy constant (K 4 = 1.35 × 105 erg/c.c.) due to the asymmetric exchange interaction between the trivalent Ce–Cr which further lifts the free energy of the system and causes lag in the onset of AFM ordering showing the significant thermal hysteresis (ΔT ∼ 10 K) in the field-cooled (FC)-warming measurement protocol as compared to the FC-cooling mode. The H–T phase diagram, mapped from the isothermal magnetization data and differential magnetic susceptibility data with different measurement protocols clearly distinguishes three prominent regions below the T N (∼150 K), viz (i) long-range canted AFM + weak FM phase (Γ4 (G z , F y , A x )), (ii) Γ24 mixed phase and (iii) robust Γ2 (F z , G y , C x ; , ) AFM + FM phases. Tunable spin–flopped transition (∼ 30 kOe), significant negative exchange-bias field (H EB ∼ 2.5 kOe), huge coercive field (H C ∼ 22 kOe) and large NM (ΔM ∼ 280 emu/mole) are the unique characteristic features of the current investigated system.

Using static linear response theory to describe field emission field enhancement and a field-induced insulator-conductor transition

Experiments on field electron emission (FE) of single carbon nanotubes (CNTs) indicate that they exhibit a nearly linear Fowler–Nordheim plot, and the field enhancement factor (FEF) near the CNT apex is independent of the applied (macroscopic) field (FM) for small radii field emitters. Recent results, based on density functional theory calculations considering CNTs with small radii, retrieved the constancy of the FEF defined in terms of the corresponding induced electron density. As a consequence, it has been reported that the constancy of the FEF with FM could be connected with the linear response of the CNT. In this paper, we reinforce this connection, considering the problem of a floating (6,6) hybrid single-walled nanotube, whose cylindrical body is an insulating one and composed of alternating boron and nitrogen atoms end-capped with carbon atoms. Our results show that the constancy of the FEF is achieved when a linear dependence between the longitudinal component of the induced system dipole moment (μi,z) and FM is observed. Two regimes of constant polarizabilities have been found at sufficiently low and high FM-values. In the intermediate range 0.3V/nm≲FM≲5 V/nm, a crossover from insulating-to-conducting behavior, exhibiting a nonlinear dependence of μi,z on FM, is found accompanied by an increase of the FEF with FM. This result reveals circumstances that could lead to dependence of the FEF on FM, being timely for interpretation of FE characteristics in the context of vacuum nanoelectronic devices.

Complex magnetic phase diagram in noncentrosymmetric EuPtAs

We report the observation of multiple magnetic transitions in single crystals of EuPtAs using magnetization, transport, and thermodynamic measurements. EuPtAs crystallizes in the noncentrosymmetric tetragonal LaPtSi-type structure (space group $I{4}_{1}md$) and undergoes a second-order antiferromagnetic (AFM) transition at 14.8 K, which is followed by a first-order transition at about 7.5 K. Both transitions are suppressed by magnetic fields applied parallel and perpendicular to the $c$ axis, and multiple field-induced transitions are observed for both field directions, leading to complex temperature-field diagrams with a domelike magnetic phase for fields parallel to the $c$ axis. Moreover, the dependence of the low-temperature resistivity on the application of a training field, together with a lack of remanent magnetization, suggests the presence of multiple AFM domains in zero field.

Robust antiferromagnetism inY2Co3

We report on a solution-growth based method to synthesise single crystals of Y$_2$Co$_3$ and on its structural and magnetic properties. We find that Y$_2$Co$_3$ crystallizes in the La2Ni3-type orthorhombic structure with space group Cmce (No. 64), with Co forming distorted kagome lattices. Y$_2$Co$_3$ orders antiferromagnetically below $T_N$ = 252 K. Magnetization measurements reveal that the moments are primarily aligned along the b axis with evidence for some canting. Band-structure calculations indicate that ferromagnetic and antiferromagnetic orders are nearly degenerate, at odds with experimental results. Magnetization measurements under pressure up to 1 GPa reveal that the N/'eel temperature decreases with the slope of -1.69 K/GPa. We observe a field-induced spin-flop transition in the magnetization measurements at 1.5 K and 21 T with magnetic field along the b direction. The magnetization is not saturated up to 35 T, indicating that the antiferromagnetic ordering in Y$_2$Co$_3$ is quite robust, which is surprising for such a Co-rich intermetallic.

Interplay between charge density wave order and magnetic field in the nonmagnetic rare-earth tritelluride LaTe3

Charge density wave (CDW) states in solids bear an intimate connection to underlying fermiology. Modification of the latter by a suitable perturbation provides an attractive handle to unearth novel CDW states. Here, we combine extensive magnetotransport experiments and first-principles electronic structure calculations on a non-magnetic tritelluride LaTe$_{3}$ single crystal to uncover phenomena rare in CDW systems: $(i)$ hump-like feature in the temperature dependence of resistivity at low temperature under application of magnetic field, which moves to higher temperature with increasing field strength, $(ii)$ highly anisotropic large transverse magnetoresistance (MR) upon rotation of magnetic field about current parallel to crystallographic c-axis, (iii) anomalously large positive MR with spike-like peaks at characteristic angles when the angle between current and field is varied in the bc-plane, (iv) extreme sensitivity of the angular variation of MR on field and temperature. Moreover, our Hall measurement reveals remarkably high carrier mobility $\sim$ 33000 cm$^{2}$/Vs, which is comparable to that observed in some topological semimetals. These novel observations find a comprehensive explication in our density functional theory (DFT) and dynamical mean field theory (DMFT) calculations that capture field-induced electronic structure modification in LaTe$_{3}$. The band structure theory together with transport calculations suggest the possibility of a second field-induced CDW transition from the field-reconstructed Fermi surface, which qualitatively explains the hump in temperature dependence of resistivity at low temperature. Thus, our study exposes the novel manifestations of the interplay between CDW order and field-induced electronic structure modifications in LaTe$_{3}$, and establishes a new route to tune CDW states by perturbations like magnetic field.

Staircase effect in field-induced metamagnetic transitions in La0·9Ce0·1Fe12B6

We report on peculiar magnetic-field-induced metamagnetic transitions in the antiferromagnetic itinerant-electron compound La0·9Ce0·1Fe12B6. Below 8 K, the first magnetization curves display multiple steep jumps generating a staircase-like shape. Whereas the magnetization of La0·9Ce0·1Fe12B6 varies smoothly with the external applied magnetic field at T ≥ 8 K. We further show that this staircase effect is extremely sensitive to the thermomagnetic history of the sample.

Tunable competing magnetic anisotropies and spin reconfigurations in ferrimagnetic Fe100−xGdx alloy films

We report a comprehensive study of the temperature evolution of in-plane (IP) and out-of-plane (OOP) effective magnetic anisotropies in compensated ferrimagnetic ${\mathrm{Fe}}_{100\ensuremath{-}x}{\mathrm{Gd}}_{x}$ alloy films by employing direct current magnetometry and radiofrequency (RF) transverse susceptibility (TS) measurements. We suggest that our ${\mathrm{Fe}}_{100\ensuremath{-}x}{\mathrm{Gd}}_{x}$ system is chemically inhomogeneous and phase segregates into Fe- and Gd-enriched regions. Our IP and OOP magnetometry results indicate that the system undergoes a temperature-driven transformation from an IP-spin-configuration-dominated state to an OOP-spin-configuration-dominated state below a certain temperature (spin reorientation temperature). A two-step reversal behavior emerges in the OOP $M$($H$) loop near compensation, which we attribute to the sequential magnetization reversals of Fe- and Gd-enriched domains. Field-induced spin-flop transitions were also observed near the compensation. Our RF TS measurements indicate that the effective magnetic anisotropy for the OOP configuration dominates over that for the IP configuration below a certain spin reorientation temperature. Both IP and OOP anisotropy fields determined from our TS measurement exhibit a minimum around the compensation temperature, which has been explained in the framework of the Stoner-Wohlfarth model.

Field-induced transition within the superconducting state of CeRh2As2.

Materials with multiple superconducting phases are rare. Here, we report the discovery of two-phase unconventional superconductivity in CeRh2As2 Using thermodynamic probes, we establish that the superconducting critical field of its high-field phase is as high as 14 tesla, even though the transition temperature is only 0.26 kelvin. Furthermore, a transition between two different superconducting phases is observed in a c axis magnetic field. Local inversion-symmetry breaking at the cerium sites enables Rashba spin-orbit coupling alternating between the cerium sublayers. The staggered Rashba coupling introduces a layer degree of freedom to which the field-induced transition and high critical field seen in experiment are likely related.

Field-controlled tunability of novel multifunctional phenomena in Tb-substituted La2CoMnO6: Role of antisite disorder

Multifunctional materials have gained huge attention owing to their great possibility in device applications. However, producing single-phase multifunctional materials, associated with various novel properties, has been proved to be a serious challenge. A simple yet effective way to overcome this barrier, is therefore of great importance. Here, we report the evolution of temperature- and magnetic field-dependent novel multifunctional phenomena in polycrystalline La2-xTbxCoMnO6. Substitution of Tb in ferromagnetic La2CoMnO6, induces antiferromagnetic ordering through development of antisite disorder and antiphase boundaries, and results in a phase separation between ferromagnetic/antiferromagnetic layers. This originates the coexistence of conventional and inverse magnetocaloric effects in this system. The switching between them, with its tunability with temperature and magnetic field, suggests a huge potential of this compound. In addition, a clear correlation is established between the magnetocaloric switching and field-induced metamagnetic transitions. Furthermore, the discovery of tunable giant exchange bias (~1.8 kOe) at very low cooling field (500 Oe), a reasonable self-exchange bias (270 Oe), and a large negative magnetoresistance (~14%), makes this system enormously attractive for practical applications and fundamental research. The present study proposes a novel and effective route for successfully preparing essential multifunctional compounds to open a new pathway toward room-temperature applications.

Experimental evidence for field-induced metamagnetic transition of EuCd2As2

Recent studies have shown that layered compound EuCd2As2 could exhibit diverse topological states depending on the different magnetic structures, such as Weyl semimetal, Dirac semimetal and topological insulator. In order to further study the interplay between magnetism and topology of EuCd2As2, it is necessary to figure out its magnetic structure. Here, by magnetization (M) measurements and negative magnetostriction (λ) along the [001] direction measured by scanning tunneling microscopy on EuCd2As2 single crystals, we observe field-induced metamagnetic phase transition from A-type antiferromagnetic (AFM) ground state to field-polarized state, with canted AFM (CAFM) state in between. Magnetization and magnetostriction are more sensitive to the in-plane field than the out-of-plane field, indicating the magnetic moments lying in the ab plane. The absence of abrupt jump on M-H and λ-H curves demonstrates that the phase transition is a second-order type. In CAFM state, M increases linearly with the field and λ is proportional to M2. Tunneling conductance spectra show the field-induced evolution of the electronic density of states. Our results provide experimental evidence for understanding the magnetic structure of EuCd2As2.

Field induced metamagnetism and large magnetic entropy change in RRhSi (R = Tb, Dy, Ho) rare earth intermetallics

We report magnetic, magneto-caloric, electronic structure, and optical properties of rare earth intermetallics RRhSi (R=Tb, Dy, Ho). These compounds show antiferromagnetic ordering at low temperatures. The magnetization data reveal field-induced metamagnetic transition in DyRhSi and HoRhSi compounds, which results in large magnetocaloric effect (MCE) in these compounds. In the case of Dy, the MCE is found to be larger than those of other analogs of the RTX family. Theoretical calculations confirm antiferromagnetic ordering in these compounds and show a negligible contribution of magnetic moment from Rh atom. The optical measurements carried out for these materials support the theoretical calculations. We uncover large magnetocaloric effect in DyRhSi and HoRhSi intermetallics attributed to metamagnetic transition and identify electronic states involved in the formation of magnetic and spectral properties based on DFT+U and optical studies.

High-field soft-x-ray dichroism of a hard ferrimagnet with easy-plane anisotropy

We performed soft x-ray spectroscopic studies of the ferrimagnet ${\mathrm{TbFe}}_{5}{\mathrm{Al}}_{7}$ with strong easy-plane anisotropy in pulsed magnetic fields up to 29 T along with bulk magnetization and magnetostriction measurements. We observed pronounced amplitude changes of x-ray magnetic circular dichroism and x-ray absorption spectra at the field-induced magnetic transition. This microscopically evidences the simultaneous rotation of the Tb $4f$ and Fe $3d$ magnetic moments from a collinear ferrimagnetic order along the [100] axis to a state with the moments close to [010], the other easy-axis direction of the tetragonal lattice in magnetic fields applied along the [100] axis. We determined the magnetic-anisotropy constant of ${\mathrm{TbFe}}_{5}{\mathrm{Al}}_{7}$ by simulating the high-field macro- and microscopic magnetization process using a two-sublattice model.

Hinge magnons from noncollinear magnetic order in a honeycomb antiferromagnet

We propose that noncollinear magnetic order in magnetic systems can harbor a higher-order topological magnon phase with non-Hermitian topology and hinge magnon modes. We consider a three-dimensional system of interacting local moments on stacked layers of honeycomb lattice. It initially favors a collinear magnetic order along an in-plane direction, which turns into a noncollinear order upon applying an external magnetic field perpendicular to the easy axis. We exploit the non-Hermitian nature of the magnon Hamiltonian to show that this field-induced transition corresponds to the transformation from a topological magnon insulator to a higher-order topological magnon state with a one-dimensional hinge mode. As a concrete example, we discuss the recently discovered monoclinic phase of thin chromium trihalides, which we propose as a promising material candidate of the higher-order topological magnon phase.

Large magnetic anisotropy and field-induced spin-flop transition in Fe2(TeO3)2(SO4)·3H2O single crystals

Single crystals of Fe2(TeO3)2(SO4)·3H2O with an alternating spin-chain structure are successfully grown by a hydrothermal method. Magnetic and heat capacity measurements show that this compound possesses a short-range antiferromagetic order at ~55 K and a long-range antiferromagetic order at 32.5 K. A large magnetic anisotropy with magnetization easy c-axis is observed, in which a weak ferromagnetic component is observed along the a- and b-axes, while a spin flop transition is observed at applied field along the c-axis. Also, the magnetic anisotropy energy at 2 K is estimated to be 4.78(3) × 108 ergs/cm3. Such magnetic anisotropy may be due to a strong nonsymmetric distortion in the FeO6 octahedra.

Magnetoelectric phase diagram and magnetic field-induced reversal of electric polarization in Ba0.5Sr1.5Mg1.6Co0.4Fe12O22 single crystal

Multiferroic Y-type hexaferrites are single-phase compounds in which the electric polarization (P) is induced by a low magnetic field (H). In this study, Y-type hexaferrite Ba0.5Sr1.5Mg1.6Co0.4Fe12O22 single crystal was synthesized using Na2CO3-Fe2O3 flux. Their structural, magnetic, and magnetoelectric properties were investigated. The different transition temperatures between the H⊥c and H//c configurations showed that the direction of the applied H was important for the spin configurations. The M-H loops exhibited that the field-induced transitions could occur at room temperature (RT). A first-order magnetic phase transition around 250 K was unveiled from the Arrott plots. The P was non-zero at zero H below 50 K. By studying the magnetic field dependence of the dielectric properties at selected temperatures, a magnetoelectric phase diagram exhibiting the evolution of the spin-induced ferroelectric order with the Hab and temperature (T) was revealed. The magnetoelectric phase diagram showed that the polarization was reversed by the magnetic fields below 150 K where the H-induced ferroelectric order was maintained in a zero magnetic field.