First-order Magnetic Phase Transition Research Articles

The magnetic phase transition and magnetocaloric effect in Sm0.58Sr0.42MnO3 nanoparticles

It is known that Sm0.58Sr0.42MnO3 (SSMO) with a first-order magnetic phase transition exhibits colossal magnetoresistance and magnetocaloric effects around the Curie temperature (TC). However, the effects just occur in a narrow temperature range due to the first-order nature. This work points out that its phase transition width and magnetocaloric effect is easily modified upon the fabrication of SSMO nanoparticles (NPs). Our detailed studies also demonstrate a clear tendency of the magnetic phase transformation from first to second order when the crystallite size (d) of NPs are reduced below 65nm. Though the d decrease usually leads to the suppression of the TC, magnetization, and magnetic-entropy change, the phase transition width is increased remarkably, thus widening the application range of SSMO. These interesting features are related to changes of the lattice strain, surface defect density, and electronic structure of Mn ions in NPs.

Magnetic lock-in phase transition in Tb0.95Er0.05Ni5 driven by low magnetic fields

The magnetic properties of a mixed inter-metallic compound, Tb0.95Er0.05Ni5, were investigated using a neutron diffraction method at low temperatures. These compounds were known to have a successive magnetic phase transition from the paramagnetic state at high temperature to a lock-in phase at low temperature through intermediate phases, i.e., PM(paramagnetic)–FM(ferromagnetic)–IC(incommensurate)–L(lock-in) in reverse order of temperature. A meta-magnetic phase transition between an IC phase and a FM phase at 9K was observed with the critical field, HMT~200mT. A new magnetic phase between the new phase (lock-in phase) and an IC phase has been observed. From the field dependence of the Bragg reflections and their satellite peaks at low temperatures (3–12K), weak field driven first-order magnetic phase transitions were recorded at six fixed temperatures. The critical magnetic field decreases exponentially with the temperature. From these experimental results, we obtained a magnetic phase diagram of Tb0.95Er0.05Ni5 at a low temperature region for the first time.

Rounding of a first-order magnetic phase transition in La0.7Ca0.3Mn0.85Ni0.15O3

We prepared a polycrystalline sample of orthorhombic La0.7Ca0.3Mn0.85Ni0.15O3, and then studied its critical behavior. Based on the Landau phase-transition theory and Banerjee's criteria, we have found the sample undergoing a second-order magnetic phase transition. This continuous transition is characterized by critical parameters of TC = 170 K, β = 0.320 ± 0.009, γ = 0.990 ± 0.082, and δ = 4.09 ± 0.17 determined from modified Arrott plots. With these values, the magnetization-field-temperature (M-H-T) behaviors of La0.7Ca0.3Mn0.85Ni0.15O3 below and above TC are well described by an equation of state M(H,ε)=εβf±(H/εβ+γ), where ε=(T−TC)/TC, f+ for T > TC and f− for T < TC. Having compared to the theoretical models, the critical-exponent values determined in our case are close to those expected for the 3D Ising model and mean-field theory. This indicates an existence of ferromagnetic short-range interactions in the system below TC. The nature of the transformation from first-order to second-order phase transitions related to the Ni doping is discussed in detail.

Effect of substrate temperature on the crystallographic structure and first-order magnetic phase transition of FeRh thin films

Abstract

Moving Domain Boundary and the Spontaneous Flow of Thermal Current Controlled by Magnetic Field in Spinel MnV2O4

Heat conduction in the system that releases or absorbs latent heat caused by the first-order phase transition gives rise to an intriguing problem. A typical example is seen in the system showing melting and solidification, where the domain boundary between the liquid and solid phase moves with time, known as moving boundary problems. We report in the present paper that a similar moving domain boundary is observed in an all-solid-state system, spinel MnV2O4, where there is a first-order magnetic phase transition and the transition temperature changes with applied magnetic field. We found that in the sample attached to a heat bath with a constant temperature, thermal current flows (without external heat source) when the magnetic field is increased or decreased, associated with the release or absorption of the latent heat. We also found that the magnitude of the spontaneous heat current depends on the sweep rate of the magnetic field. We show that the experimental results, which have a nonlinear nature, can ...

Field-induced magnetic phase transition in Pr3+ doped Sm0.5Sr0.5MnO3 manganites

Magnetic properties of Pr3+ doped Sm0.5Sr0.5MnO3 manganite with the variation of particle size down to 30 nm have been investigated in detail. We have critically examined the magnetic field (H) dependence of the order of the ferromagnetic (FM) to paramagnetic (PM) phase transition in this Sm0.35Pr0.15Sr0.5MnO3 manganite. It has been shown that all the particle sizes (bulk to nano) exhibit first order FM → PM phase transition under low magnetic field accompanied by magnetization with thermal hysteresis in the field cooled cooling and warming cycle. However, the samples exhibit a second order magnetic phase transition above a critical field HCR. Again with decreasing the particle size, the ferromagnetic transition temperature, the thermal hysteresis width in the magnetizations, and the critical field HCR significantly decrease, which indicate that the ferromagnetism is weakened and the first-order magnetic phase transition is softened. We have also used the Banerjee criteria to distinguish the first-order magnetic phase transition from the second-order one. A detailed analysis of the magnetization measurements of this manganite reveal the disorder-induced softening of the first order phase transition in this phase separated manganite.

Giant atomic displacement at a magnetic phase transition in metastable Mn3O4

We present x-ray, neutron scattering, and heat capacity data that reveal a coupled first-order magnetic and structural phase transition of the metastable mixed-valence postspinel compound Mn${}_{3}$O${}_{4}$ at 210 K. Powder neutron diffraction measurements reveal a magnetic structure in which Mn${}^{3+}$ spins align antiferromagnetically along the edge-sharing $a$ axis, with a magnetic propagation vector $k=[1/2,0,0]$. In contrast, the Mn${}^{2+}$ spins, which are geometrically frustrated, do not order until a much lower temperature. Although the Mn${}^{2+}$ spins do not directly participate in the magnetic phase transition at 210 K, structural refinements reveal a large atomic shift at this phase transition, corresponding to a physical motion of approximately 0.25 \AA{}, even though the crystal symmetry remains unchanged. This ``giant'' response is due to the coupled effect of built-in strain in the metastable postspinel structure with the orbital realignment of the Mn${}^{3+}$ ion.

Pressure-induced successive structural transitions and high-pressure tetragonal phase of Fe1.08Te

We report the effects of hydrostatic pressure on the temperature-induced phase transitions in Fe1.08Te in the pressure range 0-3 GPa using synchrotron powder x-ray diffraction (XRD). The results reveal a plethora of phase transitions. At ambient pressure, Fe1.08Te undergoes simultaneous first-order structural symmetry-breaking and magnetic phase transitions, namely from the paramagnetic tetragonal (P4/nmm) to the antiferromagnetic monoclinic (P2_1/m) phase. We show that, at a pressure of 1.33 GPa, the low temperature structure adopts an orthorhombic symmetry. More importantly, for pressures of 2.29 GPa and higher, a symmetry-conserving tetragonal-tetragonal phase transition has been identified from a change in the c/a ratio of the lattice parameters. The succession of different pressure and temperature-induced structural and magnetic phases indicates the presence of strong magneto-elastic coupling effects in this material.

Phase diagram of Ba1−xKxFe2As2

We report the results of a systematic investigation of the phase diagram of the iron-based superconductor Ba${}_{1\ensuremath{-}x}$K${}_{x}$Fe${}_{2}$As${}_{2}$ from $x$ $=$ 0 to $x$ $=$ 1.0 using high-resolution neutron and x-ray diffraction and magnetization measurements. The polycrystalline samples were prepared with an estimated compositional variation of $\ensuremath{\Delta}x$ $\ensuremath{\lesssim}$ 0.01, allowing a more precise estimate of the phase boundaries than reported so far. At room temperature, Ba${}_{1\ensuremath{-}x}$K${}_{x}$Fe${}_{2}$As${}_{2}$ crystallizes in a tetragonal structure with the space group symmetry of $I$4/mmm, but at low doping, the samples undergo a coincident first-order structural and magnetic phase transition to an orthorhombic (O) structure with the space group Fmmm and a striped antiferromagnet (AF) with the space group ${F}_{\mathrm{c}}mm$\ensuremath{'}$m$\ensuremath{'}. The transition temperature falls from a maximum of 139 K in the undoped compound to 0 K at $x$ $=$ 0.252, with a critical exponent as a function of doping of 0.25(2) and 0.12(1) for the structural and magnetic order parameters, respectively. The onset of superconductivity occurs at a critical concentration of $x$ $=$ 0.130(3), and the superconducting transition temperature grows linearly with $x$ until it crosses the AF/O phase boundary. Below this concentration, there is microscopic phase coexistence of the AF/O and superconducting order parameters, although a slight suppression of the AF/O order is evidence that the phases are competing. At higher doping, superconductivity has a maximum ${T}_{\mathrm{c}}$ of 38 K at $x$ $=$ 0.4 that falls to 3 K at $x$ $=$ 1.0. We discuss reasons for the suppression of the spin density wave order and the electron--hole asymmetry in the phase diagram.

Hysteresis and magnetocaloric effect at the magnetostructural phase transition of Ni-Mn-Ga and Ni-Mn-Co-Sn Heusler alloys

Hysteresis features of the direct and inverse magnetocaloric effect associated with first-order magnetostructural phase transitions in Ni-Mn-X (X $=$ Ga, Sn) Heusler alloys have been disclosed by differential calorimetry measurements performed either under a constant magnetic field, $H$, or by varying $H$ in isothermal conditions. We have shown that the magnetocaloric effect in these alloys crucially depends on the employed measuring protocol. Experimentally observed peculiarities of the magnetocaloric effect have been explained in the framework of a model that accounts for different contributions to the Gibbs energy of austenitic ${g}_{A}$ and martensitic ${g}_{M}$ phases. Obtained experimental results have been summarized by plotting a phase fraction of the austenite ${x}_{A}$ versus the driving force ${g}_{M}\ensuremath{-}{g}_{A}$. The developed approach allows one to predict reversible and irreversible features of the direct as well as inverse magnetocaloric effect in a variety of materials with first-order magnetic phase transitions.

A first-order magnetic phase transition near 15 K with novel magnetic-field-induced effects in Er5Si3

We present magnetic characterization of a binary rare-earth intermetallic compound Er5Si3, crystallizing in Mn5Si3-type hexagonal structure, through magnetization, heat capacity, electrical resistivity and magnetoresistance measurements. Our investigations confirm that the compound exhibits two magnetic transitions with decreasing temperature, the first one at 35 K and the second one at 15 K. The present results reveal that the second magnetic transition is a disorder-broadened first-order transition, as shown by thermal hysteresis in the measured data. Another important finding is that, below 15 K, there is a magnetic-field-induced transition with a hysteretic effect with the electrical resistance getting unusually enhanced at this transition and the magnetoresistance is found to exhibit intriguing magnetic-field dependence, indicating novel magnetic phase coexistence phenomenon. It thus appears that this compound is characterized by interesting magnetic anomalies in the temperature–magnetic-field phase diagram.

Magnetocaloric effect in layered NdMn2Ge0.4Si1.6

A giant magnetocaloric effect has been observed in NdMn2Ge0.4Si1.6 associated with the first-order magnetic phase transition from antiferromagnetism to ferromagnetism around TC=36K. The magnetic entropy change –ΔSM and adiabatic temperature change ΔTad have been determined from magnetization and specific heat measurements (B=0–5 T) with –ΔSM calculated by the Maxwell relation and Clausius–Clapeyron method. The values –ΔSMmax=12.3 J kg−1 K−1 and refrigerant capacity ∼95 J/kg for ΔB=0–2 T as derived from the Maxwell relation, together with the small hysteresis (thermal <0.5 K; magnetic field <0.1 T), indicate the potential of NdMn2Ge0.4Si1.6 for refrigeration applications.

Current-induced magnetic and thermal effects in materials with combined magnetic and resistive transitions

Current-induced effects in materials for which the first-order magnetic phase transition is accompanied by a strong change in electric resistivity are theoretically analyzed. An approach is developed that describes the magnetization and conductivity of thin film systems based on such material, for the temperature interval where two magnetic phases coexist. The changes in magnetic state and system temperature, originating from the Joule heating, are analyzed for the steady-state condition of the heat exchange with the surrounding medium. A way to achieve the temperature stabilization effect in the system is suggested. The possibility of tuning the system temperature by changing the external magnetic field is demonstrated.

Giant reversible anisotropic magnetocaloric effect in an antiferromagnetic EuFe2As2 single crystal

Here, we report the characterization of a giant reversible anisotropic magnetocaloric effect in a EuFe2As2 single crystal. The magnetic properties of EuFe2As2 single crystals are quite interesting; they display a small magnetic hysteresis, anisotropy, and a first-order magnetic phase transition. The maximum magnetic entropy change in in-plane magnetic-field direction was 14.6 J/kg K around 20 K and out-of-plane was 10.3 J/kg K around 20 K as a result of changing the magnetic field from 0 to 5 T. These results suggest the possibility of using EuFe2As2 single crystals in magnetic refrigeration applications.

Phase domain structures in cylindrical magnets under conditions of a first-order magnetic phase transition

The magnetic and resonance properties of cylindrical magnets at first-order phase transition from paramagnetic to ferromagnetic state were theoretically studied. It has been shown that in the external magnetic field directed perpendicularly to the rotation axis, formation of a specific domain structure of paramagnetic and ferromagnetic layers can be energetically favorable. The parameters of cylindrical phase domains as well as their dependences on temperature, magnetic field and material characteristics have been calculated. Peculiarities of the magnetic resonance spectra appearing as a result of the phase domain formation have been considered. Dependence of the resonance field of the system of ferromagnetic domains on magnetization and temperature has been obtained.

Clear correspondence between magnetoresistance and magnetization of epitaxially grown ordered FeRh thin films

Magnetoresistance and magnetization of the CsCl-type ordered FeRh epitaxial thin films grown on MgO(001) substrates are investigated as a function of temperature and film thickness. All the films show a clear first-order magnetic phase transition from the antiferromagnetic state to the ferromagnetic state at around 380 K. A large negative variation in the field-dependent magnetoresistance of the FeRh thin films, which is accompanied by the field-induced magnetic phase transition, is found to be well scaled with the magnetization squared M2. The results indicate that the magnetoresistance primarily arises from spin-dependent scattering through the s–d exchange interactions between conduction electrons and the localized magnetic moments.

Recent advances in the microstructure design of materials for near room temperature magnetic cooling (invited)

Successful operation of a magnetic cooling device depends crucially on the performance of active magnetic refrigerant material. Extensive research activity has been concentrated on optimizing the magnetic properties of these materials by chemical composition modification. Here, it is shown how the design of appropriate microstructure can be used to control the magnetic properties as well as mechanical stability of refrigerant materials experiencing a first-order magnetic phase transition. In particular, introducing porosity in LaFe13−xSix alloys provides long-term stability by sacrificing only a small fraction of the magnetocaloric effect and results in the desired reduction of the magnetic and thermal hysteresis by a factor of 5, as compared to bulk alloys. Reducing crystallite size down to the nanometer range is shown to substantially lower magnetic hysteresis. On the other hand, the magnetocaloric effect is weakened by about 40% and 60% in alloys with grain size of 70 and 44 nm, respectively.

The influence of the magnetoelastic interaction on the magnetocaloric effect inferrimagnetic systems: a theoretical investigation

In this work the magnetocaloric effect is theoretically investigated considering amicroscopic model Hamiltonian, which describes a magnetic system formed by twosublattices of different magnetic ions coupled by exchange and magnetoelasticinteractions. We analyze systematically several profiles of the ferrimagnetic arrangementsthat were studied earlier without the magnetoelastic interaction. The influence ofchanging the magnetoelastic parameters on the magnetization, isothermal entropychange and adiabatic temperature change curves are investigated. Depending onthe model parameters, the magnetic system shows a first-order magnetic phasetransition leading to high direct and inverse magnetocaloric effect, besides twosimultaneous first-order magnetic phase transitions which were predicted. A constantΔST = 0.4 J mol − 1 K − 1 is obtained in the simulated system in a temperature interval of 50 K, around110 K.

ChemInform Abstract: Magnetic Phase Transitions in Nanoclusters and Nanostructures

AbstractReview: 20 refs.

Improvement of refrigerant capacity of La 0.7Ca 0.3MnO 3 material with a few percent Co doping

The influence of first and second order magnetic phase transitions on the magnetocaloric effect (MCE) and refrigerant capacity or relative cooling power (RCP) of La 0.7Ca 0.3MnO 3 and La 0.7Ca 0.3Mn 0.95Co 0.05O 3 materials has been investigated. Large low-field-induced magnetic entropy changes are observed in La 0.7Ca 0.3MnO 3 and La 0.7Ca 0.3Mn 0.95Co 0.05O 3 materials. The La 0.7Ca 0.3MnO 3 material experiences a large entropy change with a first-order magnetic phase transition at the Curie temperature, T C . On the other hand, La 0.7Ca 0.3Mn 0.95Co 0.05O 3 displays a smaller entropy change with a second order phase transition. While a first-order magnetic transition material induces a larger MCE (7.528 J/kg K at 5 T) at T C , this is limited to a narrow temperature range, resulting in a relatively small RCP (218 J/kg), while the Co-doped second-order magnetic transition material induces a smaller MCE (7.14 J/kg K for 5 T), but it is spread over a broader temperature range, resulting in a larger RCP (308 J/kg). The maximum magnetoresistance (MR, defined as ρ(0)/ ρ( H)–1) under a field of 5 T is about 206% and 333% for La 0.7Ca 0.3MnO 3 and La 0.7Ca 0.3Mn 0.95Co 0.05O 3, respectively. The refrigeration capacity (RCP) is enhanced in La 0.7Ca 0.3Mn 0.95Co 0.05O 3 (by about 41%) due to small changes from Co doping. The magnetocaloric features of these materials at lower magnetic fields (MCE=3.163 for La 0.7Ca 0.3Mn 0.95Co 0.05O 3 and 4.63 J/kg K for La 0.7Ca 0.3MnO 3 at 1 T), and the high RCP and MR can provide some ideas for exploring novel magnetic refrigerants that can operate with permanent magnets rather than superconducting ones as the magnetic field source.