Field-induced Magnetic Phase Transitions Research Articles

Giant magnetocaloric effect of Ni-Co-Mn-Ti all-d Heusler alloys in high magnetic fields

Ni-Co-Mn-Ti all-d Heusler alloys are attracting considerable attention for solid-state caloric-cooling applications due to their promising combination of excellent caloric and mechanical properties. Here, we report on the maximum attainable magnetocaloric effect in Ni37Co13Mn34.5Ti15.5, which shows a first-order magnetostructural martensitic transformation around room temperature. Heat capacity measurements reveal a giant transition entropy change of 43.5J(kgK)\\protect \\relax \\special {t4ht=−}1 and are utilized to estimate the magnetocaloric effect as well as the magnetic fields required to saturate it in isothermal and adiabatic conditions. Confirming the results based on this approach, we achieve maximum isothermal entropy changes and directly measured adiabatic temperature changes of 37.8J(kgK)\\protect \\relax \\special {t4ht=−}1 and -20.2K, respectively. Thus, the herein reported maximum attainable magnetocaloric effect outperforms classical Ni-Mn-based Heusler alloys, such as Ni(-Co)-Mn-In. Especially the saturated adiabatic temperature change surpasses all previously published values of magnetic field-induced first-order phase transitions measured around room temperature in pulsed magnetic fields in recent years. Thereby, we demonstrate that Ni(-Co)-Mn-Ti Heusler alloys are particularly suitable for the application of sufficiently large external stimuli to fully induce the phase transition and exploit their intrinsically large caloric effect.

Observation of competing interactions and field-induced ferromagnetism in noncentrosymmetric cubic Nd3Te4 lattice

Unconventional magnetism is key to advancement in a variety of spintronic applications and thus needs to be explored in new materials. Here, we report the in-depth magnetic studies of noncentrosymmetric Nd3Te4 and findings support the existence of Dzyaloshinskii-Moriya interaction in addition to symmetric exchange interaction among the moments. The large magnetic irreversibility with negative magnetization in M(T) data and associated first-order magnetic transition in isothermal magnetization data suggest the competing interactions resulting in multiple magnetic phases. The gradual evolution of magnetic texture has been probed by changes in the magnetization entropy having interesting characteristics like the inverse magnetocaloric effect. Most importantly, we have probed the existing nontrivial magnetic phase under a low applied magnetic field by ac-χ(T, H) and dc magnetization (M − H) data, having the same critical field in both measurements. The existence of multiple magnetic phases which are interconnected through first-order field-induced magnetic phase transitions have been probed at low field. The transition from paramagnetic to field-induced state for larger applied fields follows a second-order.

Magnetoresistance and magnetic field-induced phase transition in two-dimensional antiferromagnet Fe1/3NbS2

We perform systematic studies on the magnetic and magnetotransport properties of Fe1/3NbS2 single crystal. Results show that Fe1/3NbS2 is an antiferromagnet with strong perpendicular magnetocrystalline anisotropy even in the paramagnetic state. The Fe1/3NbS2 nanoplate exhibits exotic magnetotransport characteristics with variation of temperature and magnetic field in the vicinity of Néel temperature. The temperature dependence of resistivity indicates that the magnetic field has a substantial effect on the Néel order of Fe1/3NbS2, and an intermediate phase occurs before the sample enters into the antiferromagnetic state. It is the field- or temperature-induced antiferromagnetic–intermediate phase and intermediate phase–paramagnetic phase transitions that lead to the novel magnetotransport characteristics in the vicinity of Néel temperature. The findings in this work will promote future studies based on two-dimensional antiferromagnetic spintronics.

Magnetic field-induced phase transition in spinor exciton-polaritons condensate

We theoretically study the magnetic phase transition of condensed exciton-polariton microcavities in an applied magnetic field. When the magnetic field is strong, all polariton spins are polarized parallel to the magnetic field as usual. On the contrary, in the weak magnetic-field region, the polariton polarization degree is negative, namely, anti-parallel to the magnetic field. For a strong magnetic field, the magnetic phase of the polaritons arises and leads to a paramagnetic, while around a weak magnetic field, with zero exciton–photon detunings, and weak Rabi splitting the spin polarization of the polaritons leads to a diamagnetic. Thus, magneto-polariton phase transition polarization originates from the competition between the polariton Zeeman effect and polariton–polariton interactions. Moreover, the polariton polarization strongly depends on the exciton–photon detuning and Rabi splitting and has a large negative value as they are both small. At last, we compare our theoretical results with the experiments and find they match each other very well.

Magnetic field-induced narrow first-order and metamagnetic phase transitions of Nd5Ge3

We report on the magnetic behaviour of Nd5Ge3 by investigating through magnetization, neutron diffraction and muon spin relaxation measurements. Temperature dependent-magnetization, muon depolarization rate (λ), initial asymmetry (A0) and the stretched exponent (β) show a clear anomaly at the Néel temperature TN ∼ 54 K. However, the short-range correlated ferromagnetic interactions below TN are inferred from the diffuse scattering mechanism as revealed by zero-field neutron diffraction data. Narrow first order phase transition is due to the competing interaction of a high temperature weak-antiferromagnetic and low temperature glassy states. Magnetic field-induced reentrant spin glass state from a magnetic glass state is observed, before it transforms to a ferromagnetic state.

Magnetic Field-Induced Phase Transition and Weak Ferromagnetism in Nonsuperconducting Optimally Doped PrBCO Cuprate

Magnetic Field-Induced Phase Transition and Weak Ferromagnetism in Nonsuperconducting Optimally Doped PrBCO Cuprate

Pressure-Tuned Classical–Quantum Crossover in Magnetic Field-Induced Quantum Phase Transitions of a Triangular-Lattice Antiferromagnet

he correspondence principle states that as quantum numbers approach infinity, the nature of a system described by quantum mechanics should match that described by classical mechanics. Quantum phenomena, such as quantum superposition and quantum correlation, generally become unobservable when a system approaches this regime. Conversely, as quantum numbers decrease, classical descriptions give way to observable quantum effects. The external approach to classical–quantum crossover has attracted research interest. This study aims to demonstrate a method for achieving such control in materials.

Magnetic Field-Induced Martensitic Phase Transition in Cr-Substituted Ni–Mn–Sb + B Shape Memory Alloys

Magnetic Field-Induced Martensitic Phase Transition in Cr-Substituted Ni–Mn–Sb + B Shape Memory Alloys

Magnetic-field-induced transitions and the inverse magnetocaloric effect at liquid helium temperatures in the Mn1-xCoxNiGe system (0.15 ≤ x < 0.80)

Magnetic field-induced phase transitions found in the Mn1-xCoxNiGe system (0.15 ≤ x < 0.8) at T = 5 K may differ in nature and magnitude of the saturation magnetization of the initial weakly magnetic phase. These differences also affect the phenomena accompanying the transitions, specifically, the inverse magnetocaloric effect (MCE). In the current work, the mechanisms of these phenomena are analyzed within the framework of the magnetostructural model, which takes into account the difference in the limiting values of the magnetic order parameters in competing orthorhombic and hexagonal crystal structures. As follows from the analysis performed, the features observed in Mn1-xCoxNiGe can be explained by the realization at low temperatures of a metastable orthorhombic crystal state in magnetically ordered phases with a stable high-temperature hexagonal crystal structure.

Magnetic field-induced phase transition in ilmenite-type CoVO3

The ilmenite-type CoVO3 undergoes an antiferromagnetic transition below 140 K, and the tetravalent vanadium ions form V–V dimers below 550 K. This paper presents the magnetic spin structure and the phase transition induced by a magnetic field in CoVO3. Neutron powder diffraction at 50 K reveals that the spins of Co2+ arrange in a zigzag order on the honeycomb lattice with no external magnetic field. This magnetic spin structure does not exhibit spontaneous magnetization, corroborating previous magnetic measurements. Magnetization measurements in a pulsed-magnetic field revealed a transition to a weak-ferromagnetic phase at 37 T (100 K) and above 50 T (4.2 K), with spontaneous magnetization approximating 0.3–0.5 μB/f.u. This phase transition could potentially be attributed to a transition to a canted antiferromagnetic phase, which is brought about by the reduction in structural symmetry due to magnetostriction.

Magnetoresistance Features at the Magnetic Field-Induced Phase Transition in FeRh Thin Films

The causes of the appearance of first-order magnetic phase transitions remain a mystery. FeRh alloy is a classical material where a first-order magnetic phase transition occurs. The authors of this article studied the phase transition from the antiferromagnetic state to the ferromagnetic state in FeRh alloy. Comparison of the magnetometry and transport properties results allowed us to determine a number of differences in the mechanisms of the phase evolution during magnetic field and temperature induced transition. This article notes the priority of the rearrangement of the micromagnetic structure of the ferromagnetic phase as a result of the induction of a phase transition by a magnetic field. The main feature of the magnetic field induced phase transition compared to the temperature induced one is the change in the micromagnetic structure of the ferromagnetic phase. The growth of a ferromagnetic phase with less scattering fields leads to asymmetric behavior when a phase transition is induced near the metastable state. We also focused on the importance of taking into account the effect of magnetostriction when analyzing the evolution of the phase transition, which leads to the irreversibility of the phase transition near a zero magnetic field.

Field-induced anisotropic magnetic phase transitions and tricritical phenomena in GdCr6Ge6

Field-induced anisotropic magnetic phase transitions and tricritical phenomena in GdCr6Ge6

Large reversible magnetocaloric effect in antiferromagnetic Er3Si2C2 compound

The magnetic properties, magnetic phase transition and magnetocaloric effects (MCE) of Er3Si2C2 compound were investigated based on theoretical calculations and experimental analysis. Based on the first principles calculations, the antiferromagnetic (AFM) ground state type in Er3Si2C2 compound was predicted and its electronic structure was investigated. The experimental results show that Er3Si2C2 compound is an AFM compound with the Néel temperature (TN) of 7 K and undergoes a field-induced first-order magnetic phase transition from AFM to ferromagnetic (FM) under magnetic fields exceeding 0.6 T at 2 K. The magnetic transition process of Er3Si2C2 compound was investigated and discussed. The values of the maximum magnetic entropy change (−ΔSMmax) and the refrigeration capacity (RC) are 17 J/(kg·K) and 193 J/kg under changing magnetic fields of 0–5 T, respectively. As a potential cryogenic magnetic refrigerant, the Er3Si2C2 compound also provides an interesting research medium to study the magnetic phase transition process.

Magnetic field induced reentrant multipolar ordering in the distorted kagome-lattice antiferromagnet Dy3Ru4Al12

We report on ultrasonic and magnetocaloric-effect measurements of the hexagonal antiferromagnet ${\mathrm{Dy}}_{3}{\mathrm{Ru}}_{4}{\mathrm{Al}}_{12}$ having a distorted kagome lattice. We observed a pronounced softening of the transverse modulus, ${C}_{44}$, above 30 T applied along [100], indicating an as-yet-unidentified magnetic field induced phase transition. We determined the field-temperature phase diagrams using pulsed magnetic fields up to 55.2 T, applied along [100] and [001]. Optimizing crystal-electric-field parameters within the mean-field approximation, we conclude that the enhancement of the field induced phase-transition temperature is due to electric quadrupolar and magnetic octupolar mediated interactions. We propose that the order parameter of the magnetic field induced phase transitions is the electric quadrupole ${O}_{zx}$, facilitated by octupole-mediated interactions.

Multiple metamagnetic transitions induced by high magnetic field in DyBi

The rare-earth monopnictide compounds have recently received considerable attention in condensed matter physics because of their correlation between magnetism, crystallographic structure, and transport. Here, we report experimental observations of high-magnetic-field-induced multiple metamagnetic transitions and magnetic structures in DyBi single crystals. The external field up to 32 T is applied in three distinct crystallographic directions as $H//[001]$, $H//[011]$, and $H//[111]$, which reveals anisotropic magnetism as well as multiple metamagnetic transitions. Two field-induced magnetic phase transitions at 3.7 T and 4.9 T along $H//[001]$, two at 3.8 T and 24 T along $H//[011]$, and one at 3.8 T along $H//[111]$ are identified. In order to unveil the nature of magnetic interaction in DyBi, the critical behavior analysis for $H//$[001], a direction with typical magnetism and transitions, is performed. The yielded critical exponents $\ensuremath{\beta}=0.234(8)$, $\ensuremath{\gamma}=0.904(3)$, and $\ensuremath{\delta}=5.03(2)$ agree well with the theoretical prediction of a tricritical mean-field model, indicating a field-induced tricritical phenomenon in this system. Comprehensive magnetic phase diagrams for $H//[001]$, $H//[011]$, and $H//[111]$ are constructed based on detailed magnetization measurement and scaling, which reveal multiple phases such as NiO-type antiferromagnetic (AFM), HoP-type AFM, forced ferromagnetic (FFM), and paramagnetic (PM) phases. Two tricritical points (TCPs) are determined at the intersections of the AFM, FFM, and PM phases, with TCP = (8.6 K, 85 kOe) for $H//$[001] and (16.8 K, 243 kOe) for $H//$[011]. The recognition of multiple phases suggests delicate and complex competition and balance between variable couplings in this system.

Crystal Growth, Structural Transition, and Magnetic Properties of Ho5Pd4Sn12.

Single crystals and polycrystalline samples of Ho5Pd4Sn12 have been synthesized using flux and arc-melting methods, respectively. Single-crystal X-ray diffraction studies indicate that Ho5Pd4Sn12 crystallizes in a tetragonal structure (I4/m) at room temperature and transforms into a monoclinic structure (C2/m) below ∼194 K. This structural transition is further supported by a transmission electron microscopy study and an anomaly at ∼194 K in the specific heat data. Temperature-dependent resistivity data also show a kink around the structural transition temperature. Ho5Pd4Sn12 is antiferromagnetically ordered below 7 K. Ho5Pd4Sn12 shows magnetic anisotropy, and the isothermal magnetization curve (H⊥c) at 2 K exhibits a field-induced magnetic phase transition around 22.8 kOe.

Static magnetic and ESR spectroscopic properties of the dimer-chain antiferromagnet BiCoPO5

We report a comprehensive study of the static susceptibility, high-field magnetization and high-frequency/high-magnetic field electron spin resonance (HF-ESR) spectroscopy of polycrystalline samples of the bismuth cobalt oxy-phosphate BiCoPO$_5$. This compound features a peculiar spin system that can be considered as antiferromagnetic (AFM) chains built of pairs of ferromagnetically coupled Co spins and interconnected in all three spatial directions. It was previously shown that BiCoPO$_5$ orders antiferromagnetically at $T_{\rm N} \approx 10$ K and this order can be continuously suppressed by magnetic field towards the critical value $\mu_0H_{\rm c} \approx 15$ T. In our experiments we find strongly enhanced magnetic moments and spectroscopic $g$ factors as compared to the expected spin-only values, suggesting a strong contribution of orbital magnetism for the Co$^{2+}$ ions. This is quantitatively confirmed by ab initio quantum chemical calculations. Within the AFM ordered phase, we observe a distinct field-induced magnetic phase transition. Its critical field rises to $\sim 6$ T at $T \ll T_{\rm N}$. The HF-ESR spectra recorded at $T\ll T_{\rm N}$ are very rich comprising up to six resonance modes possibly of the multimagnonic nature that soften towards the critical region around 6 T. Interestingly, we find that the Co moments are not yet fully polarized at $H_{\rm c}$ which supports a theoretical proposal identifying $H_{\rm c}$ as the quantum critical point for the transition of the spin system in BiCoPO$_5$ to the quantum disordered state at stronger fields.

Investigating field-induced magnetic order in Han purple by neutron scattering up to 25.9 T

BaCuSi$_2$O$_6$ is a quasi-two-dimensional (2D) quantum antiferromagnet containing three different types of stacked, square-lattice bilayer hosting spin-1/2 dimers. Although this compound has been studied extensively over the last two decades, the critical applied magnetic field required to close the dimer spin gap and induce magnetic order, which exceeds 23 T, has to date precluded any kind of neutron scattering investigation. However, the HFM/EXED instrument at the Helmholtz-Zentrum Berlin made this possible at magnetic fields up to 25.9 T. Thus we have used HFM/EXED to investigate the field-induced ordered phase, in particular to look for quasi-2D physics arising from the layered structure and from the different bilayer types. From neutron diffraction data, we determined the global dependence of the magnetic order parameter on both magnetic field and temperature, finding a form consistent with 3D quantum critical scaling; from this we deduce that the quasi-2D interactions and nonuniform layering of BaCuSi$_2$O$_6$ are not anisotropic enough to induce hallmarks of 2D physics. From neutron spectroscopy data, we measured the dispersion of the strongly Zeeman-split magnetic excitations, finding good agreement with the zero-field interaction parameters of BaCuSi$_2$O$_6$. We conclude that HFM/EXED allowed a significant extension in the application of neutron scattering techniques to the field range above 20 T and in particular opened new horizons in the study of field-induced magnetic quantum phase transitions.

The tuning of oxalato-bridge on magnetic interaction and field-induced phase transition in Ba2Co2Cl2(C2O4)3·4H2O

The crystal structure of the oxalato-bridged compound Ba2Co2Cl2(C2O4)3·4H2O has C2/c symmetry and contains two types of oxalate-bridged modes. We have investigated the magnetization behavior of the Ba2Co2Cl2(C2O4)3·4H2O sample with both the static and pulsed magnetic fields. The Bleaney-Bowers fitting for the temperature dependence of magnetization shows that there are two different spin-dimers with the different intra- and inter-dimer interactions. Using the high field sweep rate of the pulsed magnetic field, magnetization measurements show four continuous phase transitions (with four different critical magnetic fields) in a smaller magnetic field range from 5.5 to 7 T, which also confirms there are two different dimers. Based on the structure analysis, the four phase transitions might result from four different magnetic exchange interactions (J1, J'1, J2 and J'2) in the two different dimers. Thus, in the design of the molecular-based magnetic materials, the oxalato-bridged and its various bridging modes can be used to mediate the magnetic interaction of the intra- and inter-dimers, the electronic effect between the metal ions and induce new phases.

Interesting magnetic response of the nuclear fuel material UO2

ABSTRACT We report results of dc magnetization measurements on UO2. Our study reveals a deviation from standard Curie-Weiss (CW) paramagnetic behavior below 280 K, and that is followed by a transition to antiferromagnetic state with marked thermomagnetic irreversibility below TN = 30.6 K. The zero field cooled (ZFC) magnetization exhibits distinct structures not usually observed in the antiferromagnets, whereas field cooled (FC) magnetization looks more like a ferromagnet. The thermomagnetic irreversibility continues to exist in a subtle way even in the paramagnetic regime well above TN . This behavior along with the deviation from CW law highlight non-standard nature of the paramagnetic state. Magnetic response below TN changes significantly with the increase in the applied magnetic field. In the isothermal magnetic field variation of magnetization, a subtle signature of a magnetic field-induced phase transition is observed. All these experimental results highlight the non-trivial nature of the magnetic state in UO2.