Metamagnetic Phase Transition Research Articles

Asymmetric magnetic relaxation behavior of domains and domain walls observed through the FeRh first-order metamagnetic phase transition

The phase coexistence present through a first-order phase transition means there will be finite regions between the two phases where the structure of the system will vary from one phase to the other, known as a phase boundary wall. This region is said to play an important but unknown role in the dynamics of the first-order phase transitions. Here, by using both x-ray photon correlation spectroscopy and magnetometry techniques to measure the temporal isothermal development at various points through the thermally activated first-order metamagnetic phase transition present in the near-equiatomic FeRh alloy, we are able to isolate the dynamic behavior of the domain walls in this system. These investigations reveal that relaxation behavior of the domain walls changes when phase coexistence is introduced into the system and that the domain wall dynamics is different to the macroscale behavior. We attribute this to the effect of the exchange coupling between regions of either magnetic phase changing the dynamic properties of domain walls relative to bulk regions of either phase. We also believe this behavior comes from the influence of the phase boundary wall on other magnetic objects in the system.

Reduced Annealing Time and Enhanced Magnetocaloric Effect of La(Fe, Al)13 Alloy by La-nonstoichiometry and Si-doping

LaFe13−xMx (M = Si, Al) alloys are promising for use in magnetic refrigeration. However, they require long annealing time (30 days) in order to optimize the magnetocaloric properties. Research has shown that the addition of extra La in off-stoichiometric alloys can greatly shorten the annealing time. Therefore, the purpose of this study is to investigate the influence of the extra addition of La on the annealing properties of a new off-stoichiometric La1.7Fe11.6Al1.4−xSix (x = 0, 0.1, 0.4) alloys. It was demonstrated that after a 36h annealing time, a large volume fraction of 1:13 magnetocaloric phase was obtained for all alloys. Further microstructural analysis of the off-stoichiometric La1.7Fe11.6Al1.4−xSix alloys revealed a facet-like grain morphology. The La1.7Fe11.6Al1.4 and La1.7Fe11.6Al1Si0.4 alloys were shown to contain large 1:13 phase precipitates separated in a La-rich matrix, while the La1.7Fe11.6Al1.3Si0.1 alloy had a continuous 1:13 phase matrix with a fine dispersion of La-rich precipitates throughout. When the magnetic field varied between 0 and 2 T, the corresponding magnetic entropy change and relative cooling capacity for the La1.7Fe11.6Al1.3Si0.1 specimen were determined as 4.58 J/kg K and 173.6 J/kg, respectively. More importantly, the La1.7Fe11.6Al1.3Si0.1 alloy displayed only a slight volume change when the meta-magnetic phase transition occurred, which is promising for cyclic use.

Competing magnetic orders in quantum critical Sr3Ru2O7

We investigated Sr$_3$Ru$_2$O$_7$, a quantum critical metal that shows a metamagnetic quantum phase transition and electronic nematicity, through density functional calculations. These predict a ferromagnetic ground state in contrast to the experimentally observed paramagnetism, raising the question of competing magnetic states and associated fluctuations that may suppress magnetic order. We did a search to identify such low energy antiferromagnetically ordered metastable states. We find that the lowest energy antiferromagnetic state has a striped order. This corresponds to the E-type order that has been shown to be induced by Mn alloying. We also note significant transport anisotropy in this E-type ordered state. These results are discussed in relation to experimental observations.

Interstitial Effects on the Magnetic Phase Transition and Magnetocaloric Effects in (Hf, Ta)Fe2 Kagome Phase

The effects of Ta substitution on the first-order phase transition have been firstly studied in Hf1-xTaxFe2 (x = 0.15, 0.165, 0.18) alloys with kagome-type lattice. Higher Ta substitution leads to the reduced metamagnetic transition temperature (Tt) from low-temperature ferromagnetism to high-temperature antiferromagnetism and paramagnetism. By doping C atoms, the Tt is gradually reduced and thermal hysteresis becomes widened in the alloys with higher Ta substitution. The critical field which triggers the metamagnetic phase transition is not substantially affected by interstitial C atoms. With increased Ta substitution, for the field change of 7 T, the maximum of magnetic entropy change (ΔSmax) of 3.7 J kg−1 K−1 is obtained at x = 0.15 and enhanced to 4 J kg−1 K−1 at x = 0.165 but reduced to ~ 3.21 J kg−1 K−1 in Hf0.82Ta0.18Fe2 alloy. By C addition, both Tt and the temperature where ΔS is maximized are shifted to a lower temperature, especially in the higher Ta-contained alloys.

Direct measurements of the magnetocaloric effect of Fe49Rh51 using the mirage effect

The magnetocaloric effect in the Fe49Rh51 alloy was systematically studied using three different approaches: in-field differential scanning calorimetry, standard direct measurement of the adiabatic temperature change, and a non-contact method based on a thermo-optical phenomenon, the mirage effect, which was able to directly test the magnetocaloric response induced by a fast magnetic field variation. The metamagnetic phase transition of Fe49Rh51 was studied in the temperature range of 290–330 K at magnetic fields up to 1.8 T through magnetic and calorimetric measurements. The estimated parameters of phase transition were comparable with the literature data. The values of adiabatic temperature change obtained with the three methods (calorimetry, standard direct measurement, and mirage-based technique), which explore three different time scales of the field variation (static field, 1 T s−1, 770 T s−1), were consistent, proving the absence of dynamic constraints in the first-order magnetostructural transition at the maximum field sweep rate.

Evidence for weak ferromagnetism and metamagnetic phase transitions in frustrated antiferromagnetic systems with octahedral structure

Possible source of the weak ferromagnetism and the metamagnetic phase transitions in the antiferromagnetic systems with octahedral structure, such as perovskites, is identified in the framework of the antiferromagnetic spin-1/2 Ising model on the octahedral recursive lattice. It is shown that the weak ferromagnetism of the studied antiferromagnetic model is directly related to the competition between two qualitatively different kinds of spin loops (frustrated and bipartite) realized within each elementary octahedron. The free energy of the model is found, the magnetization properties of the model are studied, and the phase diagram of the metamagnetic phase transitions in the external magnetic field is determined. The discrete system of the model ground states is found and discussed. The discontinuity of the susceptibility at the metamagnetic phase transitions is studied. The exact expression for the Néel temperature of the antiferromagnetic system is determined and compare to the Curie temperature of the ferromagnetic system.

Large Negative Thermal Expansion and Magnetoelastic Coupling in Metamagnetic Tetragonal (Mn, T)2Sb (T = Cr, V) Alloys

Metamagnetic phase transition of Mn2-xCrxSb (x = 0.07, 0.09, and 0.11) and Mn2-yVySb (y = 0.1, 0.15) alloys had been studied. More Cr and V substitutions lead into increased phase transition temperature, which is confirmed by differential scanning calorimetry (DSC) measurement. The maximized saturation magnetostriction (λs//) of − 1350 ppm and − 610 ppm under 7 T have been realized in Mn1.93Cr0.07Sb alloy and Mn1.9V0.1Sb alloy, respectively, and gradually decreased with more substitution. Giant negative thermal expansion (NTE) is triggered by metamagnetism. The highest linear coefficient of − 42.4 ppm/K is obtained in Mn1.93Cr0.07Sb alloy, but almost zero expansion is obtained in Mn1.85V0.15Sb alloy. The coincident highest ΔSmax associated with the maximized λs// in both Mn2-xCrxSb (x = 0.07, 0.09, and 0.11) and Mn2-yVySb (y = 0.1, 0.15) systems suggests that the strong magnetoelastic coupling is also beneficial to enhance the magnetic entropy change.

Electronic and magnetic properties of EuNi2−δSb2 structural variants

X-ray diffraction, magnetic susceptibility, magnetization, heat capacity and electrical resistivity results are reported for single crystals of two structural variants of EuNi2−δSb2 that crystallize in the CaBe2Ge2 and ThCr2Si2-type structures. While the former occurs with a stoichiometric ratio, the latter exhibits a Ni site vacancy (δ = 0.36). Both systems exhibit similar magnetic behavior at elevated temperatures, where there is an isotropic Curie–Weiss temperature dependence that indicates an antiferromagnetic exchange interaction between divalent europium ions, although it is stronger for the CaBe2Ge2-variant. At low temperatures, the differing structural environments that surround the Eu ions result in distinct ordering behavior. The CaBe2Ge2-variant orders antiferromagnetically near TN1 = 6.9 K and then undergoes a first order phase transition at TM = 4.6 K. The ThCr2Si2-variant exhibits simpler behavior, with antiferromagnetic ordering at TN2 = 5.6 K. For both compounds, an applied magnetic field suppresses the ordering temperatures and induce metamagnetic phase transitions, while applied pressure causes the ordering temperatures to increase. From these results, EuNi2−δSb2 emerges as a useful system in which to study the impact of structural variation on magnetism in a Eu-based metal.

Magnetic properties of a spin-2 antiferromagnet with metal-radical hybrid spins

We present an $S=2$ antiferromagnet composed of a Mn-verdazyl complex $[\mathrm{Mn}{(\mathrm{hfac})}_{2}]\phantom{\rule{0.16em}{0ex}}[o\text{\ensuremath{-}}\mathrm{Py}\text{\ensuremath{-}}\mathrm{V}\text{\ensuremath{-}}{(4\text{\ensuremath{-}}\mathrm{F})}_{2}]$. An analysis of the magnetic behavior reveals that the strong antiferromagnetic intramolecular interaction between spins on ${\mathrm{Mn}}^{2+}$ and the verdazyl radical forms an $S=2$ hybrid spin below approximately 100 K. In the low-temperature regions, the magnetic susceptibility and the specific heat indicate a phase transition to the three-dimensional order of the $S$ = 2 system. Below the transition temperature, the magnetization curve exhibits a metamagnetic phase transition. From the analysis of electron spin resonance modes, we evaluate the on-site biaxial anisotropy responsible for the anisotropic magnetic behavior.

Temperature-dependent lattice dynamics of antiferromagnetic and ferromagnetic phases of FeRh

We have investigated lattice dynamics of antiferromagnetic and ferromagnetic phases of cubic $(B2)$ FeRh at various temperatures from first principles using the temperature-dependent effective potential method. We have shown that already at low temperature the cubic structure of the antiferromagnetic phase becomes dynamically stable, which eliminates the contradiction between experimental observations and previous theoretical results showing its dynamical instability at temperature $T$ = 0 K. In addition, we have observed a significant difference in the temperature dependence of lattice vibrations of the ferromagnetic and antiferromagnetic phases. The phonon spectrum of the FM phase softens much stronger than that of the AFM phase, which provides additional contribution to the increase of vibrational entropy of the FM phase at high temperatures. The calculated difference between the vibrational entropies of the FM and AFM phases at a metamagnetic transition temperature (350 K) is 16 J/kg/K. This value is comparable with the experimental value of the total entropy change. We therefore conclude that the lattice dynamics plays a decisive role in the metamagnetic phase transition in FeRh and its remarkable magnetocaloric properties.

Topography dependence of the metamagnetic phase transition in FeRh thin films

The equiatomic alloy FeRh is of great scientific and technological interest due its highly unusual first-order antiferromagnetic (AF) to ferromagnetic (FM) phase transition. Here we report an exploration of the interplay between topography and phase evolution with a comprehensive magnetic force microscopy study of nominal 50 nm thick FeRh thin films and subtractively patterned wires of width 0.2 µm–2 µm. In continuous films where the surface morphology had not been optimised for smoothness, the topographical variation was observed to dominate the distribution of the magnetic transition temperatures and dictates the nucleation and growth of the magnetic phases. This observation was repeated for patterned elements, where the effects of surface morphology were more significant than those of spatial confinement. These results have clear implications for future studies of low-dimensional FeRh films, as surface topography must be considered when analysing and comparing the transition behaviour of FeRh thin films.

Synthesis, Structure and Magnetic Properties of Mn2Tb2 Tetranuclear Complex with p‐tert‐Butylthiacalix[4]arene

AbstractA new tert‐buthylthiacalix[4]arene‐based tetranuclear 3d‐4f metal complex with the Mn2Tb2 core has been synthesized and its molecular and crystal structures have been studied by X‐ray diffraction. The complex geometry is similar to that of the earlier synthesized tert‐buthylthiacalix[4]arene‐based M2Ln2 complexes with M=Mn(II), Co(II), and Ln=Gd, Pr, Eu, but unlike those systems, it exhibits intricated cooperative low‐temperature magnetic properties arising from the presence of intercluster interactions. At T<8.5 K the complex shows weak spin‐canted ferromagnetism and field induced metamagnetic phase transition. The paramagnetic behavior observed at temperatures higher than 8.5 K is similar to that previously reported for the Mn2Gd2 complex, this being indicative of the existence of competitive ferro‐ and antiferromagnetic intracluster interactions.

Entropy of Conduction Electrons from Transport Experiments

The entropy of conduction electrons was evaluated utilizing the thermodynamic definition of the Seebeck coefficient as a tool. This analysis was applied to two different kinds of scientific questions that can—if at all—be only partially addressed by other methods. These are the field-dependence of meta-magnetic phase transitions and the electronic structure in strongly disordered materials, such as alloys. We showed that the electronic entropy change in meta-magnetic transitions is not constant with the applied magnetic field, as is usually assumed. Furthermore, we traced the evolution of the electronic entropy with respect to the chemical composition of an alloy series. Insights about the strength and kind of interactions appearing in the exemplary materials can be identified in the experiments.

First order metamagnetic transition in Vanadium doped charge ordered Pr0.5Ca0·5MnO3

Magnetic properties of 5% non-magnetic V5+ (3 d0) substituted Pr0.5Ca0·5Mn0·95V0·05O3 (PCMVO) polycrystalline manganite have been studied in the temperature range 5–300 K and applied magnetic field up to 3 T. Magnetization study shows that the substitution of V at the Mn site drives the system towards a coexisting antiferromagnetic (AFM)-ferromagnetic (FM) ground state. The charge ordering and ferromagnetic phase transitions are observed at TCO = 240 K and TC = 43 K respectively. Non-saturation of magnetization below TC and a history dependent first order metamagnetic AFM-FM phase transition was observed too. During forward and reverse field sweeping a large irreversibility in magnetization indicates spin memory effect and a potential application of the sample in spintronics. These magnetic properties of the sample are attributed to the interplay between charge, orbital and magnetic ordering.

Magnetic field-induced metamagnetic, magnetocaloric and pyrocurrent behaviors of Eu2CoMnO6

In this paper, the structural, transport, pyrocurrent and magnetic behaviors of Eu2CoMnO6 (ECMO) sample are reported. It was prepared by the solid-state reaction method and crystallized in monoclinic crystal structure with a space group of P21/n. A systematic study of the temperature and magnetic field-dependent susceptibility revealed a complex magnetic behavior with field-induced type-II metamagnetic phase transition of the first-order. The multiple sharp jumps in the initial magnetization curve for T < 10 K could be attributed to structural distortion related to the martensite-like strains from E*-type antiferromagnetic to ferromagnetic ordering. The metastable magnetic behavior for T ≥ 60 K is ascribed to a transformation of the low-field disordered spin glass phase to long-range ordered ferromagnetic phase, induced by critical fields. These critical fields are quite sensitive to the direction and magnitude of the field-cooling process. The temperature-dependent magnetocaloric effect with maximum value of ~3.3 J kg−1K−1 at TC ~ 123 K and the electrical transport behavior of ECMO were studied. Further, temperature dependent pyroelectric current and polarization data of ECMO are investigated.

Magnetocaloric Effect in Alloy Fe49Rh51 in Pulsed Magnetic Fields up to 50 T

Magnetocaloric effect (MCE) in pulsed magnetic fields up to 50 T was directly studied in alloy Fe49Rh51. An inverse MCE ΔT ≈ –8 K is observed at different initial temperatures around the metamagnetic phase transition upon field rising to 20 T; further growth of the field to 50 T leads to a decrease in the absolute adiabatic temperature change by nearly 1 K, which is due to the direct MCE and proves that the whole sample undergoes a transition into the ferromagnetic phase. Upon the field decrease, the maximal absolute value of the adiabatic temperature change of |ΔT| = 9.8 K was revealed at 6 T when the initial temperature is 310 K.

Магнитокалорический эффект в сплаве Fe-=SUB=-49-=/SUB=-Rh-=SUB=-51-=/SUB=- в импульсных магнитных полях до 50 T

The direct magnetocaloric effect (MCE) was measured in pulsed magnetic fields up to 50 T in the Fe49Rh51 alloy. At different initial temperatures in the metamagnetic phase transition with an increase in the field up to 20 T, a reverse MCE ∆T ≈ -8 K is observed, while a further increase in the field to 50 T results in a decrease in the absolute value of the adiabatic temperature change by ~ 1 K, which is connected with direct MCE and indicates a complete transition of the sample into the ferromagnetic phase. The maximum of the absolute value of the adiabatic temperature change |∆Т| = 9.8 K with a decrease in the magnetic field of 6 T on initial temperature of 310 K was observed.

Beyond the isotropic Lifshitz endpoint

The puzzle of the disappearance of isotropic Lifshitz points in condensed matter physics is explained from the point of view of the Wilsonian renormalization group. In analogy to the commensurate ideas of metamagnetic phase transitions, we describe the physics of thermodynamic states beyond an isotropic Lifshitz endpoint. Such phenomenon may be understood in terms of a statistically isotropic environment of coexisting multiple helicoidal and non-helicoidal states. In addition to the magnetic and condensed matter discussions, we consider also an interesting example in the context of cosmic evolution.

Ab initio study of FeRh alloy properties

Abstract In this work the structural, energetic, thermodynamic, magnetic and thermoelectric properties of FeRh alloy have been studied using first-principles calculations. The structural and magnetic results obtained for the FM phase are in agreement with experimental and other theoretical calculated values (local magnetization of about 3 μB and 1 μB for Fe and Rh atoms respectively). The transition AFM to the FM state is accompanied by a 2.4% increase in the volume of the cell and by 9.6% in the Fe spin magnetic moment. The characterization of the AFM phase shows a distortion of the cubic and tetragonal cell to the orthorhombic solving the instabilities observed in the phonon band structures curves of the corresponding to cubic structure. The stability of the AFM configurations was corroborated with molecular dynamics (MD) simulations. The magnitude of the Seebeck coefficient increases with the temperature at a certain chemical potential. While the magnitude of the electrical conductivity does not present meaningful changes with the temperature in the selected values, the thermal conductivity increases with the temperature. Another consequence of the AFM to FM transition is the drop of the resistivity ρ in the FM phase as compared to the AFM state. Based on the results obtained using MD simulations from stable AFM configurations and the results of entropy changes, the configuration AFM-B (type I) could be identified as the most favorable in achieving the metamagnetic phase transition.

PNR study of the phase transition in FeRh thin films

The first order antiferromagnetic to ferromagnetic metamagnetic phase transition of equiatomic FeRh offers new opportunities for novel antiferromagnetic memories and spintronic devices with the caveat that it can be utilized in thin film structures (&amp;lt;50 nm). Here, we report a polarized neutron reflectivity (PNR) study for three representative film thicknesses (5, 20, and 50 nm) aimed at determining the physical and magnetic structure of FeRh at room temperature and partway through the transition. The PNR results are analyzed with reference to X-ray diffraction, X-ray reflectivity, and atomic force microscopy data which together provide a consistent description of the magnetic and physical state of the FeRh thin films. The data demonstrate that the nucleation of the ferromagnetic phase initiates at the MgO substrate, and results from structural and magnetic measurements demonstrate that the magnetic behavior and strain properties of FeRh correlate with the evolving topography of the three films investigated.