Multiple Magnetic Transitions Research Articles

Multiple Magnetic Phase Transitions and Giant Refrigerant Capacity in a GdDyHoErTm High-Entropy Alloy.

Magnetocaloric high-entropy alloys (HEAs) have recently garnered significant interest owing to their potential applications in magnetic refrigeration, offering a wide working temperature range and large refrigerant capacity. In this study, we thoroughly investigated the structural, magnetic, and magnetocaloric properties of equiatomic GdDyHoErTm HEAs. The as-cast alloy exhibits a single hexagonal phase, a randomly distributed grain orientation, and complex magnetism. In particular, multiple magnetic phase transitions occur over a wide temperature range in this rare-earth HEA, which is attributed to the diverse magnetic properties of the constituent rare-earth elements. Accordingly, a table-like magnetocaloric effect (the maximum magnetic entropy change of 7.5 J/kg K at 5 T) is achieved in the temperature range of 27-175 K, leading to a giant refrigerant capacity of 923 J/kg and relative cooling power of 1110 J/kg. Our findings in the rare-earth HEAs with multiple magnetic phase transitions open up a pathway to further develop high-performance magnetocaloric materials in the field of cryogenic magnetic refrigeration.

Multiple magnetic transitions and anomalous magnetocaloric effect in an arc melting TbMn2 compound

Magnetic properties of Mn-base alloys are obviously influenced by Mn-content. In this work, multiple magnetic transitions and anomalous magnetocaloric effect of an arc melting TbMn2 intermetallic compound were measured and discussed. TbMn2 shows paramagnetic properties at room temperature. The small bulge at ∼ 230.3 K suggests the rise of a Griffiths phase. The long-range ferromagnetic ordering is established at TC ∼ 60.0 K. The observed antiferromagnetic transition at TN ∼ 45.0 K is caused by the collapse of Mn moments. At ∼ 20.2 K, an unexpected spin reorientation transition is probably due to the arrangement of the sublattice of rare earth. The field induced metamagnetic transition below TN results in an anomalous magnetocaloric effect.

Crystal growth and magnetic properties of atom K embedded in Na5Co15.5Te6O36

In this paper, we report the structural, magnetic and specific heat properties of a new compound Na2.67K1.33Pb0.67Co15.33Te6O36 (NKPCTO). The compound can be regarded as a new system charactered by the K and Pb atom embedded in the Kagome system Na5Co15.5Te6O36 (NCTO). In the new structure, we find that the disordered occupations of the Na and Co(3) atoms is irrelevant to K atom site, and Pb has same site with K. The ground state is proposed to have an effective S = 1/2 due to the 3d7 Co2+ ion in octahedral coordination and considerable spin–orbit coupling. Magnetic and specific heat data uncover that only an antiferromagnetic phase transition develops in NKPCTO at 49 K. There are also ferromagnetic correlations above the Neel temperature, as well as anomalous hysteresis loops and multiple field-induced magnetic transitions at low temperatures.

Direct and inverse magnetocaloric effects in magnetostrictive GdMn2Ge2 with field-induced metamagnetic transition

Heavy rare-earth-based ternary intermetallic compounds with the formula RT2X2 have drawn great interest because of their multiple magnetic transitions and various magnetic structures. Here, anisotropic magnetic behaviors, magnetocaloric effects (MCEs), and magnetostriction effects in single-crystalline GdMn2Ge2 are studied in two different directions. Experiments show a magnetic transition characterized by a sudden decrease in magnetization for μ0H//a and a sharp increase for μ0H//c at Tt. The transition is driven by lower temperatures for μ0H//a, contrasting that for μ0H//c with an increase in the magnetic field. An inverse MCE is observed for μ0H//a with a maximum magnetic entropy change (−ΔSMmax) of −7.4 J kg−1 K−1 (μ0ΔH = 6 T), while a direct MCE is obtained for μ0H//c with an −ΔSMmax of 8.0 J kg−1 K−1 under the same magnetic field change. Moreover, a remarkable field-induced metamagnetic transition and a magnetostriction effect are observed simultaneously at Tt, indicating strong magneto-lattice coupling. The T-μ0H phase diagrams are constructed based on the magnetic properties. The coexistence of direct and inverse MCEs is discussed and is due to the spin-flop of Mn and anisotropic magnetic properties under magnetic fields in different directions.

Magnetism in the axion insulator candidate Eu5In2Sb6

Eu5In2Sb6 is a member of a family of orthorhombic nonsymmorphic rare-earth intermetallics that combines large localized magnetic moments and itinerant exchange with a low carrier density and perpendicular glide planes. This may result in special topological crystalline (wallpaper fermion) or axion insulating phases. Recent studies of Eu5In2Sb6 single crystals have revealed colossal negative magnetoresistance and multiple magnetic phase transitions. Here, we clarify this ordering process using neutron scattering, resonant elastic x-ray scattering, muon spin-rotation, and magnetometry. The nonsymmorphic and multisite character of Eu5In2Sb6 results in coplanar noncollinear magnetic structures with an Ising-like net magnetization along the a axis. A reordering transition, attributable to competing ferro- and antiferromagnetic couplings, manifests as the onset of a second commensurate Fourier component. In the absence of spatially resolved probes, the experimental evidence for this low-temperature state can be interpreted either as an unusual double-q structure or in a phase separation scenario. The net magnetization produces variable anisotropic hysteretic effects which also couple to charge transport. The implied potential for functional domain physics and topological transport suggests that this structural family may be a promising platform to implement concepts of topological antiferromagnetic spintronics. Published by the American Physical Society 2024

Multiple magnetic transition and magnetocaloric properties in the mixed valence Eu8CuNi2.5Si42.5 type I clathrate compound

We investigated the magnetocaloric and electrical transport properties of the Eu8CuNi2.5Si42.5 clathrate compound, synthesized by an arc melting and annealing method. X-ray photoemission spectroscopy revealed a mixed valence state of Eu2+ and Eu3+. The low-field and low-temperature magnetic measurements indicated a multiple magnetic transition, from ferromagnetic near 35 K to antiferromagnetic at 25 K. Increasing the magnetic field led to the broadening of antiferromagnetic peaks and a final ferromagnetic state under high magnetic fields, indicative of spin reorientation. The transition from a ferromagnetic to an antiferromagnetic state was further corroborated by specific heat measurements. We noted spontaneous magnetization at low temperatures via magnetic hysteresis and Arrott plot analysis. The coexistence of an antiferromagnetic ground state (attributed to the Eu2+ ions) and ferromagnetic clusters (associated with the Ni2+ ions) was supported by spontaneous magnetization at low temperatures in the antiferromagnetic state. The magnetocaloric analyses revealed a high spin entropy change over a broad temperature range for Eu8CuNi2.5Si42.5, which implies its potential as a robust low-temperature magnetocaloric material, distinguished by its high refrigerant capacity.

Unusual multiple magnetic transitions and anomalous Hall effect observed in antiferromagnetic Weyl semimetal, Mn2.94Ge (Ge-rich).

We report on the magnetic and Hall effect measurements of the magnetic Weyl semimetal, Mn2.94Ge (Ge-rich) single crystal. From the magnetic properties study, we identify unusual multiple magnetic transitions below the Ne'el temperature of 353 K, such as the spin-reorientation (TSR) and ferromagnetic-like transitions. Consistent with the magnetic properties, the Hall effect study shows unusual behavior around the spin-reorientation transition. Specifically, the anomalous Hall conductivity increases with increasing temperature, reaching a maximum atTSR, which then gradually decreases with increasing temperature. This observation is quite in contrast to the Mn3+δGe (Mn-rich) system, though both compositions share the same hexagonal crystal symmetry. This study unravels the sensitivity of magnetic and topological properties on the Mn concentration.

Er-driven incommensurate to commensurate magnetic phase transition of Fe in the spin-chain compound BaErFeO4

Magnetic phase transitions and structures of the spin-chain compound BaErFeO4 were investigated by measurements of magnetic properties (specific heat, magnetic susceptibility) and neutron diffraction. The lattice geometry of the orthorhombic crystal structure (space group ) of the BaRFeO4 compounds (R=Dy–Yb, Y) supports frustrations which lead to multiple magnetic phase transitions with complex magnetic structures. BaErFeO4 undergoes three successive magnetic phase transitions at TN1=49K, TN2=33.4K, and TN3=3.4K. In contrast with the previously investigated BaRFeO4 (R=Y, Tm, Yb) compounds, all with incommensurate magnetic propagation vectors k1=(0,0,kz), BaErFeO4 is the first member in this series that shows a phase transition from an incommensurate (k1 below TN1) to a commensurate magnetic structure with k2=(12,0,12) below TN2. In the crystal structure, all magnetic ions (Fe1, Fe2, Er1, and Er2) are part of chains propagating along the b axis. Below TN1, strong antiferromagnetic (AFM) Fe-Fe spin-exchange coupling between square pyramidal (Fe1) and octahedral (Fe2) centers generates a collinear AFM structure with a constant size of the ordered Fe moments and a constant magnetic phase inside each chain of Fe3+ cations. Exchange coupling between the Fe chains is much weaker. At TN2, 3d−4f exchange interactions induce an ordered moment at the Er3+ ions, which results in a change of the direction of the ordered Fe moments from the b direction (above TN2) to inside the ac plane (below TN2) and a change from an incommensurate (k1 above TN2) to a commensurate (k2 below TN2) AFM structure. Toward lower temperature, 4f−4f exchange interactions become stronger and create at TN3 a constant magnetic phase inside each chain of Er3+ cations. At TN2 and TN3, the magnetic susceptibility shows sharp decreases that coincide with large increases of the correlation length of the magnetic structure. The unique magnetic structures of BaErFeO4 are compared with those of other BaRFeO4 compounds by considering experimental and theoretical aspects. ©2024 American Physical Society 2024 American Physical Society

Alloying effect of rare-earth tritellurides on the charge density wave and magnetic properties

Among many van der Waals materials rare-earth tritellurides (RTe3) allow studying several phenomena like magnetic, superconducting, and charge density wave (CDW). These studies show the effect of cationic alloying of antiferromagnetic RTe3 for fully tunable near room-temperature CDW properties. DyxGd1−xTe3 and DyxTb1−xTe3 alloys were synthesized through a chemical vapor transport technique, and the rare-earth element composition was controlled by changing the ratio of rare-earth metal reagents. The results show that the lattice parameters can be continuously tuned with the composition of the rare-earth cations leading to the variation of the internal chemical pressure. Temperature-dependent Raman spectroscopy and electric transport measurement show that the CDW transition temperature (TCDW) of RTe3 alloys varies with lattice parameters/chemical pressure spanning across 300–380 K. Additional magnetism studies offer the first insights into the magnetic ordering in RTe3 alloys. The emergence of multiple magnetic transitions implies complex magnetic interactions that arise from interactions between different rare-earth elements. Overall findings introduce ways to control the CDW behavior and provide valuable insights into the magnetic ordering in RTe3 alloys, contributing to further investigation and a better understanding of their properties.

Spin-phonon coupling driven magnetodielectric effect in low-dimensional complex magnetic BaGdFeO4 system

In this report, we have investigated the detailed magnetodielectric properties associated with spin-phonon coupling in the BaGdFeO4 polycrystalline compound, X-ray diffraction study confirms the orthorhombic crystal structure with a space group of Pnma. The DC magnetization measurements indicate the complex magnetic behavior with multiple magnetic transitions at TN1 = 62 K and TN2 = 31 K. In the field-dependent magnetization study, field-induced metamagnetic transitions and their temperature dependence have been attributed to the competing magnetic interactions of two magnetic sub-lattices with rare-earth (Gd3+) and Fe3+ magnetic spins. Dielectric measurements have revealed the correlation of observed dielectric anomalies with the magnetic transitions. The frequency-independent and magnetic field-dependent dielectric anomalies, along with the corresponding magnetic transitions, thus corroborate the subtle magnetodielectric coupling studied by temperature-dependent magnetodielectric measurements. We discuss possible origins for the magnetodielectric behavior in terms of weak spin-phonon interactions, as confirmed by the temperature-dependent Raman spectra measurements.

Multiple magnetic transitions, metamagnetism, and large magnetoresistance in GdAuGe single crystals

Multiple magnetic transitions, metamagnetism, and large magnetoresistance in GdAuGe single crystals

Effect of synthesis temperature on crystal structure, optical and magnetic properties of SmCuO3-δ ceramic phosphor

Effect of synthesis temperature on crystal structure, optical and magnetic properties of SmCuO3-δ ceramic phosphor is investigated in this work. The SmCuO3-δ ceramic has been synthesized using a sol-gel method. Rietveld analysis reveals that SmCuO3-δ ceramic crystallizes into coexisting tetragonal (I4/mmm) and monoclinic (C2/c) crystal structures. The phase fraction of the tetragonal and monoclinic phases strongly depends on the synthesis temperature. The crystallite size and particle size increase with increasing calcination temperature. The X-ray photoelectron spectroscopic spectra reveal the presence of (Cu2+, Cu3+) and (Sm2+, Sm3+) ions alongwith the oxygen vacancy centres in the phosphor. The SmCuO3-δ ceramic shows multiple magnetic phase transitions. The FTIR spectra show the presence of vibrational bands due to Cu-O and Sm-O groups. The optical band gap of the SmCuO3-δ phosphor decreases with an increase in calcination temperature and crystallite size. The photoluminescence excitation spectra show the peaks at 363, 402, 505 and 542 nm at the fixed emission wavelength of 609 nm, whereas the photoluminescence emission spectra contain peaks at 465, 515 and 609 nm at the fixed excitation wavelength of 402 nm. The photoluminescence emission intensity of the sample increases with the rising calcination temperature upto 900 °C and finally, it quenches at 1000 °C. Therefore, the SmCuO3-δ ceramic phosphor may be useful for solid state lighting, LEDs and magnetic devices.

Multiple magnetic transitions induced by Mn-doping in orthochromite HoCrO3

It has been established that both hybridization with magnetic rare earth cation and crystal field originating from structural anisotropy can affect the spin orientation of magnetic transition metal perovskite. In this work, we have systematically studied the crystal structure, magnetization, and magnetic structure of Mn-doped rare earth orthochromites HoCr1−xMnxO3 (x = 0–0.85) by means of X-ray diffraction, magnetometry, and neutron powder diffraction. With increasing Jahn–Teller active Mn3+-substitution for Cr3+, the crystallographic distortion is gradually enhanced and causes a systematic evolution of magnetism. With doping, the Cr(Mn) ordering temperature is gradually suppressed, and multiple magnetic configurations Γ2, Γ1, and Γ4 phases appear consecutively. The rich transition phenomena are ascribed to a competition between increased structural anisotropy and weakened Ho-Cr(Mn) hybridization with doping. In a low doping regime with x = 0.1–0.5, Γ2 phase is predominant in low temperature, and a magnetization reversal is observed, reflecting the opposite sign of Cr-Mn DMI coefficient with respect to the Cr-Cr and Mn-Mn interaction. In the high doping range with x = 0.6–0.8, the long-range order of Cr(Mn) sublattice is gradually suppressed while a short-range order becomes dominant. For x = 0.85, a magnetic structure resembling o-HoMnO3 is observed.

Impact of strain on the magnetocaloric effect of oxide heterostructures

We report a detailed study of the magnetocaloric effect in heterostructures of La2NiMnO6 and La2/3Sr1/3MnO3. The shape, width and magnitude of the temperature dependence of the magnetic entropy change (ΔSm) for these multilayer samples are affected by their layout with a clear impact from epitaxial strains on each layer. A large ΔSm over a wide temperature range which goes beyond room temperature is observed in all samples. We observe a temperature-independent table-top-like ΔSm over a temperature range as large as 100K in the trilayer samples. La2NiMnO6 double perovskite with multiple magnetic phase transitions sensitive to strain is the key to tuning and shaping the temperature dependence of the magnetic entropy changes to suit the requirements of several cooling cycles.

Multiple Magnetic Phase Transitions and Critical Behavior in Single-Crystal SmMn2Ge2

Magnetic materials with noncollinear spin configurations have engendered significant interest in condensed matter physics due to their intriguing physical properties. We direct our attention towards the magnetic properties and critical behavior of single-crystal SmMn2Ge2, an itinerant magnet with numerous temperature-dependent magnetic phase transitions. Notably, SmMn2Ge2 displays significant magnetic anisotropy with easy magnetization direction switching from the c axis to the ab plane as temperature decreases. The critical behavior of the ferromagnetic transition occurring above room temperature is thoroughly examined. Reliable and self-consistent critical exponents, including β = 0.292(2), γ = 0.924(8), and δ = 4.164(6), along with the Curie temperature T c = 347 K, are extracted through various methods, which provide evidence for the coexistence of multiple magnetic interactions in SmMn2Ge2. Further analysis reveals that the magnetic interaction of SmMn2Ge2 is a long-range type with the interaction distance decaying as J(r) ∼ r −4.35.

The modulation of magnetism and charge carrier in magnetic topological insulator MnBi4Te7 by Pb and Sb co-doping

The intrinsic magnetic topological insulator (MTI) MnBi2Te4 family containing magnetic order and nontrivial topology are fantastic materials for studying exotic topological states, such as quantum anomalous Hall effect, but the strong antiferromagnetic (AFM) coupling hinders potential practical applications. Here, we carry out magnetic and transport measurements on (Mn(1−x)Pbx)Bi4Te7 (0 ≤ x ≤ 0.52) single crystals. As x increases from 0 to 0.45, the AFM exchange interaction is gradually weakened by the dilution of magnetic moments. When x reaches up to 0.52, the AFM coupling is completely suppressed and it turns into a ferromagnetic -like ground state. Additionally, Sb substitutions on Bi sites in this system can not only alter the charge carriers but also further influence the magnetism and bring multiple magnetic phase transitions under low temperatures. Our results demonstrate a MTI candidate with adjustable magnetic ground state and charge carriers in Pb and Sb co-doped MnBi4Te7, which provides a promising platform to study rich topological quantum phases and benefits the potential applications in the future.

Magnetic and Magnetotransport Properties of the Magnetic Topological Nodal‐Line Semimetal TbSbTe

AbstractThe magnetic properties, magneto‐resistivity, Hall resistivity, Seebeck coefficient, and heat capacity are investigated for a magnetic topological nodal‐line semimetal TbSbTe. The calculated energy‐band structures of TbSbTe show two nodal rings on the kx‐ky planes, and the Fermi surface possesses one electron pocket with an enclosure of one hole pocket around the Γ point. The multiple magnetic phase transitions are induced at critical magnetic fields of Hc1 ≈ 10.5 kOe, Hc2 ≈ 20.8 kOe, and Hc3 ≈ 38.2 kOe at 2 K for the H // ab plane. Temperature dependence of electrical resistivity displays a hump‐like feature around 240 K, a general positive slope above TN = 6 K but a negative slope below TN. The magnetoresistance exhibits a conversion from the semi‐classical H2 dependence at weak fields to the linear‐field dependence at high fields, indicating the presence of a Dirac linear energy dispersion. TbSbTe may provide an ideal platform for studying topological physics and designing devices based on topological quantum materials.

Low-temperature and elastic properties of the 1/1 Tsai-type quasicrystal approximant GdCd6 investigated by ultrasonic measurements

Low-temperature and elastic properties of the quasicrystal approximant GdCd6 have been investigated by means of an ultrasonic measurement. Salient elastic anomalies were observed in the temperature and magnetic field dependence of the principal elastic constants, most probably being associated with the successive multiple magnetic phase transitions showing up at low temperatures. Based on the experimental data, a magnetic field vs temperature phase diagram was constructed. In a zero magnetic field, at least four phases appear to exist. However, the phase diagram both for the magnetic field applied for H// and H// is richer, and interestingly some phase boundaries correspond to the development of field-induced phases, leading to the intricate magnetic phase diagram possibly with multiple ordered phases. We discuss the elastic and electronic properties at low temperatures, and also the nature of the multiple magnetic phase transitions of GdCd6.

Sawtooth lattice multiferroic BeCr2O4 : Noncollinear magnetic structure and multiple magnetic transitions

Noncollinear magnetic structures and multiple magnetic phase transitions in a sawtooth lattice antiferromagnet consisting of ${\mathrm{Cr}}^{3+}$ are experimentally identified in this work, thereby proposing the scenario of magnetism-driven ferroelectricity in a sawtooth lattice. The title compound, ${\mathrm{BeCr}}_{2}{\mathrm{O}}_{4}$, displays three magnetic phase transitions at low temperatures---at ${T}_{N1}\ensuremath{\approx}7.5$ K, at ${T}_{N2}\ensuremath{\approx}25$ K, and at ${T}_{N3}\ensuremath{\approx}26$ K---revealed through magnetic susceptibility, specific heat, and neutron diffraction in this work. These magnetic phase transitions are found to be influenced by externally applied magnetic fields. Isothermal magnetization curves at low temperatures below the magnetic transitions indicate the antiferromagnetic nature of ${\mathrm{BeCr}}_{2}{\mathrm{O}}_{4}$ with two spin-flop-like transitions occurring at ${H}_{c1}\ensuremath{\approx}29$ kOe and ${H}_{c2}\ensuremath{\approx}47$ kOe. Our high-resolution x-ray and neutron diffraction studies, performed on single crystal and powder samples, unambiguously determined the crystal structure as orthorhombic $Pbnm$. By performing the magnetic superspace group analysis of the neutron diffraction data at low temperatures, the magnetic structure in the temperature range ${T}_{N3,N2}<T<{T}_{N1}$ is determined to be the polar magnetic space group $P21nm.{1}^{\ensuremath{'}}(00g)0s0s$ with a cycloidal magnetic propagation vector ${\mathbf{k}}_{1}=(0,0,0.090(1))$. The magnetic structure in the newly identified phase below ${T}_{N1}$ is determined as $P21/b.{1}^{\ensuremath{'}}[b](00g)00s$ with the magnetic propagation vector ${\mathbf{k}}_{2}=(0,0,0.908(1))$. The cycloidal spin structure determined in our work is usually associated with electric polarization, thereby making ${\mathrm{BeCr}}_{2}{\mathrm{O}}_{4}$ a promising multiferroic belonging to the sparsely populated family of sawtooth lattice antiferromagnets.

Interplay of magnetic and electric coupling across the spin density wave to conical magnetic ordering in a BaHoFeO4 spin-cluster chain compound

In this study, we performed a detailed analysis of the magnetoelectric properties of a polycrystalline BaHoFeO4 system. Rietveld refinement of the synchrotron x-ray powder diffraction pattern (SXRD) with space group Pnma confirmed that the orthorhombic crystal structure was preserved down to the lowest temperature (T) = 15 K. The DC magnetization indicated complex magnetic behavior with multiple magnetic transitions at TN1 = 49 K, TN2 = 36 K, and TN3 = 7 K. The complex interplay of 3d and 4f magnetic sublattices, and the competing interactions of two different Fe-sites can explain the field (H)-induced metamagnetic behavior in BaHoFeO4 at T < TN3 and TN3< T < TN2, respectively. A strong anomaly in the dielectric constant (ε′) was observed near TN2 and TN3, which exemplified the coupling between magnetism and dielectric properties. The magnetodielectric (MD) coupling measurements via ε′ (T, H) under different H confirmed the unprecedented magnetoelectric (ME) nature with MD sign changes at the onset of TN1, TN2, and TN3 magnetic transitions; subsequently, the ME H-T phase diagram was constructed. Furthermore, the thermal variation in the lattice parameters exhibited minute changes at TN2. Spin-spiral calculations demonstrated that the spin moments of the Fe atoms are modulated in the ab-plane, whereas the spin moments of the Ho atoms can point in any direction. Our results demonstrate that the interplay between the complex magnetic modulation of Ho and Fe magnetic sublattices may play a vital role in the ME properties of BaHoFeO4.