Multiple Magnetic Transitions Research Articles

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.

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.

A new compound Na5Mn4(PO4)4F4·2H2O with a rarely mixed valence spin chain showing multiple magnetic transitions

A new mixed valence Mn3+/Mn2+ spin-chain compound Na5Mn4(PO4)4F4·2H2O shows multiple magnetic transitions at low temperature.

Single crystal growth and properties of the polar ferromagnet Mn1.05Bi with Kagome layers, huge magnetic anisotropy and slow spin dynamics

The synthesis, structure, and properties of single crystalline ${\mathrm{Mn}}_{1.05}\mathrm{Bi}$ in the polar space group $Fdd2$ are reported. ${\mathrm{Mn}}_{1.05}\mathrm{Bi}$ is isostructural to the previously reported ${\mathrm{Mn}}_{1.05}{\mathrm{Rh}}_{0.02}\mathrm{Bi}$, with both ordered interstitials and ordered vacancies of Mn leading to Kagome-like layers. The ordering of the interstitials breaks inversion symmetry and forces the material into a polar space group. DC magnetization reveals ferromagnetic properties with a huge magnetic anisotropy, with the magnetization pinned along the $a$ axis (the stacking axis), and multiple magnetic transitions which retain this anisotropy. AC measurements confirm these transitions and show very sluggish spin dynamics along the $a$ axis, with a very large temperature-dependent out-of-phase response. Heat-capacity measurements reveal the presence of Schottky defects, and resistivity measurement confirms the transitions and reveal the material to be dominated by magnetic scattering. Overall, ${\mathrm{Mn}}_{1.05}\mathrm{Bi}$ shows magnetic properties markedly different from hexagonal, NiAs-type MnBi, driven by ordered interstitials and vacancies of Mn, stabilizing a likely complex magnetic structure with strongly temperature-dependent spin dynamics. This is supported by density-functional theory calculations, which suggest a strongly anisotropic noncollinear ground state driven by Kagome layers and asymmetric Mn environments.

Multiple magnetic transitions and magnetocaloric effect of Tb4CoIn alloy

We report on the magnetic, magnetocaloric, thermal, and electrical transport properties of Tb4CoIn alloy, which crystallizes in two phases, Tb6Co2.1In0.8 (space group Immm) and Tb2In0.9Co0.1 (space group P63/mmc), respectively. The alloy reveals three successive magnetic transitions around T1 (163 K), T2 (50 K), and T3 (29 K), respectively, associated with paramagnetic to ferromagnetic transition and two sequential antiferromagnetic transitions. The low-temperature transition T3 follows the first-order magnetic behavior and exhibits the field-induced magnetic transition. Meanwhile, T2 and T1 are found to be second-order in nature which opens a possibility for hysteresis-free magnetocaloric application. The magnetocaloric properties are determined using different magnetocaloric figures of merits such as –ΔSM, ΔTad, RCP, and TEC (10). Additionally, the universal curve behavior in the isothermal entropy change unveils the variation in critical exponents around T1 and T2 due to the magnetic inhomogeneity in the alloy. Besides, the electrical transport properties of the metallic alloy denote the maximum magnetoresistance of −10% around T1.

Magnetic complexity, magnetodielectric effect and DFT calculations on correlation driven Gd2CoMnO6 insulator

In the family of Re2CoMnO6 manganite double perovskites, in contrast to parent La2CoMnO6 compound, Gd2CoMnO6 exhibits multiple magnetic transitions; ferromagnetic (FM) ordering, TC ∼ 112 K followed by AFM transition, TN ∼ 47 K, Gd spins ordering for T < 10 K and large isothermal entropy changes. A study of DC field-superimposed AC magnetic susceptibility measurements revealed the field-induced magnetic glassy behavior below TC and enhancement of FM correlations above TC. From the analysis of Almeida-Thouless behavior and dynamical power-law fit to frequency dependent AC susceptibility, Gd2CoMnO6 exhibits a volume spin glass-like nature below the freezing temperature, Tf ∼ 117.5 K. The isothermal field-dependent magnetic and dielectric permittivity data and temperature dependent Raman measurements (reported in ref. R. X. Silvaet al., J, Appl. Phys. 114 194,102 (2013)) confirms the spin-phonon coupling induced magnetodielectric effect. Further, the ground-state electronic structure and magnetic properties of Gd2CoMnO6 are investigated using DFT + U formalism with Vienna Ab-initio Simulation Package (VASP) code and predicted the material to be a correlation-driven insulator. The correlation value of the Hubbard U parameter at the 4f-Gd elements changes the stability of the magnetic state from Ferri to FM spin alignment for Ueff ≥ 3 eV and is correlated to the experimentally observed field-induced transformation of the short-range-order FiM/spin-glass-like phase into the long-range ordered FM phase.

Magneto-structural coupling induced multiple magnetic transitions and magnetocaloric effect of Ni43Mn46Sn9Ge2 alloy

Multiple magnetic and structural phase transitions and magnetocaloric effect of Ni43Mn46Sn9Ge2 Heusler alloy were detailedly investigated. The martensitic and inverse-martensitic transitions occur at temperatures slightly below room temperature, which induces a ferromagnetic - antiferromagnetic transition and large inverse magnetocaloric effect. A paramagnetic - ferromagnetic and antiferromagnetic - ferromagnetic transition was observed in high-temperature austenitic and low-temperature martensitic phase, respectively. The evident thermomagnetic irreversibility at low temperatures of the martensitic phase suggests a reentrant spin glass state, which originates from the frustration of the competing ferromagnetic and antiferromagnetic spins and results in the visible exchange bias, large coercivity and double-shifted hysteresis behaviors. A T-μ0H phase diagram was finally constructed.