Antiferromagnetic Transition Research Articles

Enhanced coercivity and emergent spin-cluster-glass state in 2D ferromagnetic material, Fe[formula omitted]GeTe[formula omitted

Two-dimensional (2D) van der Waals (vdW) magnetic materials with high coercivity and high TC are desired for spintronics and memory storage applications. Fe3GeTe2 (F3GT) is one such 2D vdW ferromagnet with a reasonably high TC, but with a very low coercive field, HC (≲100 Oe). Here we present a phase-engineered sample of F3GT with enhanced coercivity (7–10 times), without compromising its fundamental magnetic properties (TC≃ 210 K). The parent F3GT phase is infused with a small percentage of randomly embedded clusters of a coplanar FeTe (FT) phase, which serves as both mosaic pinning centers between grains of F3GT above its antiferromagnetic transition temperature (TC1∼ 70 K) and also as anti-phase domains below TC1. As a result, the grain boundary disorder and metastable nature are greatly augmented, leading to highly enhanced coercivity, cluster spin glass, and meta-magnetic behavior. The enhanced coercivity (≃1 kOe) makes F3GT-2 much more useful for memory storage applications.

Dark field X-ray microscopy below liquid-helium temperature: The case of NaMnO2

Dark field X-ray microscopy (DFXM) is an experimental technique employed to investigate material properties by probing their ‘mesoscale,’ or microscale structures, in a bulk-sensitive manner using hard X-rays at synchrotron radiation sources. However, challenges remain when it comes to applications of this technique to examine low-temperature phenomena in quantum materials, which exhibit complex phase transitions at cryogenic temperatures. One such material is NaMnO2, which hosts an antiferromagnetic transition at 45 K that is suspected to coincide with local structural transitions from its majority monoclinic phase to nanoscale triclinic domains. Direct observation of local heterogeneities and this effect at low temperatures in NaMnO2 is an important step in understanding this material, and serves as an ideal candidate study for expanding the DFXM experimental design space. This paper details a foundational high-resolution DFXM study, down to liquid‑helium temperature and below, conducted to explore phase transitions in NaMnO2. The outlined experiment ushers in the evaluation of other functional materials at low temperatures using this technique.

Antiferromagnetic order and its interplay with superconductivity in CaK(Fe1−x Mn x )4As4

The magnetic order for several compositions of CaK(FeMn x )4As4 has been studied by nuclear magnetic resonance (NMR), Mössbauer spectroscopy, and neutron diffraction. Our observations for the Mn-doped 1144 compound are consistent with the hedgehog spin vortex crystal (hSVC) order which has previously been found for Ni-doped . The hSVC state is characterized by the stripe-type propagation vectors and just as in the doped 122 compounds. The hSVC state preserves tetragonal symmetry at the Fe site, and only this SVC motif with simple antiferromagnetic (AFM) stacking along c is consistent with all our observations using NMR Mössbauer spectroscopy, and neutron diffraction. We find that the hSVC state in the Mn-doped 1144 compound coexists with superconductivity, and by combining the neutron scattering and Mössbauer spectroscopy data we can infer a quantum phase transition, hidden under the superconducting dome, associated with the suppression of the AFM transition temperature (T N) to zero for x ≈ 0.01. In addition, unlike several 122 compounds and Ni-doped 1144, the ordered magnetic moment is not observed to decrease at temperatures below the superconducting transition temperature (T c).

Multiple magnetic transitions and complex magnetic structures in Fe2SiSe4 with the sawtooth lattice

The sawtooth lattice shares some structural similarities with the kagome lattice and may attract renewed research interest. Here we report a comprehensive study on the physical properties of ${\mathrm{Fe}}_{2}{\mathrm{SiSe}}_{4}$, an unexplored member in the olivine chalcogenides with the sawtooth lattice of Fe. Our results show that ${\mathrm{Fe}}_{2}{\mathrm{SiSe}}_{4}$ is a magnetic semiconductor with band gap of 0.66 eV. It first undergoes an antiferromagnetic transition at ${\mathrm{T}}_{m1}=110$ K, then an ferrimagneticlike one at ${\mathrm{T}}_{m2}=50$ K, and finally a magnetic transition at ${\mathrm{T}}_{m3}=25$ K, which is likely driven by the thermal populations of spin-orbit manifold on the Fe sites. Neutron diffraction analysis reveals a noncollinear antiferromagnetic structure with propagation vector ${\mathbf{q}}_{\mathbf{1}}=(0,0,0)$ at ${\mathrm{T}}_{m2}<\mathrm{T}<{\mathrm{T}}_{m1}$. Interestingly, below ${\mathrm{T}}_{m2}$, an additional antiferromagnetic structure with ${\mathbf{q}}_{\mathbf{2}}=(0,0.5,0)$ appears, and ${\mathrm{Fe}}_{2}{\mathrm{SiSe}}_{4}$ exhibits a complex double-$\mathbf{q}$ magnetic structure which has never been observed in sawtooth olivines. Density functional theory calculations suggest this complex noncollinear magnetic structure may originate from the competing antiferromagnetic interactions for both intra- and interchain in the sawtooth lattice. Furthermore, band-structural calculations show that ${\mathrm{Fe}}_{2}{\mathrm{SiSe}}_{4}$ has quasi-flat-band features near the valence and conduction band structure. Our results have shown that ${\mathrm{Fe}}_{2}{\mathrm{SiSe}}_{4}$ could serve as a new material playground for further research on magnetic devices and the flat-band effect through chemical doping.

Structural and magnetic interplay in multiferroic Ho0.5Nd0.5Fe3(BO3)4

Rare-earth iron borates, $R{\mathrm{Fe}}_{3}{({\mathrm{BO}}_{3})}_{4}$ ($R$ = rare earth), are of considerable interest because of their structural and magnetic complexities due to the involvement of both $3d$ and $4f$ magnetic interactions in a helical lattice. Among them ${\mathrm{Ho}}_{0.5}{\mathrm{Nd}}_{0.5}{\mathrm{Fe}}_{3}{({\mathrm{BO}}_{3})}_{4}$ has attracted the most attention, as it exhibits a multiferroic property with a large, spontaneous, and magnetic-field-induced electric polarization ($P$) below the antiferromagnetic transition temperature (${\mathrm{T}}_{N}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}32$ K). This compound has been reported to be noncentrosymmetric (nonpolar) down to the lowest temperature, and the origin of spontaneous electric polarization below ${\mathrm{T}}_{N}$ is not known. By utilizing temperature-dependent synchrotron x-ray powder diffraction, we report here the observation of structural phase transition, i.e., the lowering of crystal symmetry from $R32$ to $P{3}_{1}21$ below ${\mathrm{T}}_{N}$ in ${\mathrm{Ho}}_{0.5}{\mathrm{Nd}}_{0.5}{\mathrm{Fe}}_{3}{({\mathrm{BO}}_{3})}_{4}$, which is further confirmed by single-crystal x-ray diffraction measurements as well as substantiated by dielectric and Raman spectroscopic results. With the help of x-ray resonant magnetic scattering, we have studied the element-specific magnetic ordering behavior, and by combining all the results, we show that the spontaneous electric polarization below the antiferromagnetic ordering transition emerges through the p-d hybridization mechanism associated with the ${\mathrm{FeO}}_{6}$ octahedra. The observations of subtle structural changes at low temperature and element-specific magnetic ordering behavior provide a comprehensive understanding of the multiferroicity in this family of compounds.

Study of low-temperature magnetic properties of the antiferromagnetic topological insulator Sm-doped MnBi2Te4

MnBi2Te4 is the first discovered intrinsic magnetic topological insulator. It has great research significance and is related to new phenomena such as topological magneto-electric effect and quantum anomalous Hall effect (QAHE). We report first doping of rare-earth elements in MnBi2Te4 crystals. MnBi2Te4 crystalline samples with different Sm doping ratios were synthesized, and Sm atoms may enter the lattice and replace Mn atoms. Low-temperature magnetization measurements show that, in addition to the antiferromagnetic (AFM) transition of MnBi2Te4, some doped samples undergo small-scale ferromagnetic transitions at around 15 K. Doping furthermore reduces the magnetic field required for the transition to the canted AFM (CAFM) state and slightly increases the Néel temperature of the crystal. Our results suggest that doping rare-earth elements may be a feasible method for tuning the magnetism of MnBi2Te4 and for future applications of magnetic topological insulators.

Observation of c -axis magnetization at low temperatures in the weak ferromagnet FeBO3 reveals a spin-reorientation transition

The weak ferromagnet $\mathrm{Fe}{\mathrm{BO}}_{3}$ is well known for being a unique system for modeling and testing magnetic dynamics primarily due to relatively simple and localized magnetic structure and its interesting spin wave dynamics. At room temperature, it has slightly canted iron moments lying in the $a\text{\ensuremath{-}}b$ plane that result in a strong antiferromagnetic moment and a weak ferromagnetic moment, which results in pronounced ferromagnetic and antiferromagnetic spin modes. However, some previous studies have shown unusual low-temperature behavior that suggests a phase transition. By performing low-temperature magnetization measurements, both in bulk and on the mesoscale, we have observed a low-temperature magnetic texture in this material in which a large $c$-axis magnetization occurs. Magnetic fields along the $c$ axis as high as 1300 Oe were observed close to the sample's surface. This presents evidence for the onset of a Morin transition or another type of spin-reorientation phase transition wherein the ${\mathrm{Fe}}^{3+}$ moments would acquire a $c$-axis component to their canting below a critical temperature. The observation of this $c$-axis magnetization suggests that there is a different ground state in this material than has been previously expected and could be due to as yet unexplored intricacies of the Dzyaloshinskii-Moriya interaction.

The magnetic ground state of Ba(Fe1/2Sn1/2)O3-δ: A potential giant dielectric material for technological applications

Ba(Fe1/2Sn1/2)O3-δ (BFSO) is a potential environmental friendly compound for miniaturization of electronic devices as it exhibits giant dielectric constant at room temperature. However, its magnetic ground state is not settled. We present here comprehensive investigation of the as-sintered and oxygen-annealed BFSO samples using x-ray diffraction, dielectric, x-ray photoelectron spectroscopy (XPS), dc magnetization (M(T, H, t)) and specific heat measurements. Both samples crystallize in a cubic Pm-3m symmetry. At room temperature, both samples show a giant dielectric constant of the order of ε' ∼104 and two low-temperature dielectric relaxations resulting from polaron-hoping and Maxwell-Wagner effect, respectively. The temperature-dependent dc magnetization and specific heat measurements on as-sintered and oxygen-annealed BFSO samples confirm the absence of long-range ordered antiferromagnetic transition at TN ∼55 K. Further, both samples show history-dependent irreversibility of zero-field cooled warming (ZFCW) and field cooled warming (FCW) M(T) curves at the irreversibility temperature (Tirr ∼18 K) with a peak in the ZFCW M(T) curve at the spin-glass freezing temperature Tf ∼16 K. In addition, the FCW M(T) curve of both samples show plateauing over a small temperature range before it starts increasing below Tf, a characteristic typically observed in cluster/spin-glass systems. The presence of long-time magnetic relaxation and aging effect in both samples further support the spin-glass behavior. We also discussed the impact of oxygen vacancies on the physical and magnetic properties and possible origin of the glassy ground state in BFSO.

Spin Seebeck effect and thermal properties of zigzag graphene nanoribbons with edge magnetism

Zigzag graphene nanoribbons (GNRs), demonstrating edge magnetism, are fascinating materials for electronic and spintronic applications. In this paper, we investigate with explicit consideration of electron-phonon scattering the Seebeck effect and thermal conductivity at various carrier densities in zigzag GNRs, which undergo antiferromagnetic, ferromagnetic, and paramagnetic transitions. Seebeck coefficients are spin dependent in ferromagnetic zigzag GNRs and can have opposite signs for the majority and the minority spin carriers, which enables the separation of spin carriers spatially under a thermal gradient. The electronic thermal conductivity is small compared to the lattice thermal conductivity, except for GNRs in the ferromagnetic state. A 100% increase in thermal conductivity is expected at antiferromagnetic to ferromagnetic transition. These results demonstrate that zigzag GNRs are also materials of high interest for spin caloritronics.

Direct and inverse magnetocaloric effects in the antiferromagnetic rare earth (RE) rich RE6Ni2.25Al0.75 (RE = Dy, Ho and Er) compounds

The magnetic refrigeration (MR) by utilizing the magnetocaloric effect (MCE) of magnetic solids has been considered a promising, environmentally benign, energy-efficient cooling technology. However, the lack of promising magnetic substances has slowed the development of its active application. To identify suitable candidate materials, we herein identified the structural and magnetic properties together with the MCE and magnetocaloric performances of rare earth (RE) rich RE6Ni2.25Al0.75 (RE = Dy, Ho and Er) compounds. All the RE6Ni2.25Al0.75 compounds are confirmed to crystallized in orthogonal Ho6Co2Ga-type structure and underwent paramagnetic to antiferromagnetic magnetic transitions. Moreover, large direct (conventional) and inverse MCEs have been observed in all the RE6Ni2.25Al0.75 compounds. The values of peak magnetic entropy changes, temperature-averaged magnetic entropy changes with 5 K-lift and relative cooling powers under magnetic field change of 0–7 T are evaluated to be − 4.44 J/kg-K, − 4.38 J/kg-K and 230.6 J/kg for Dy6Ni2.25Al0.75, to be − 12.68 J/kg-K, − 12.26 J/kg-K and 378.2 J/kg for Ho6Ni2.25Al0.75, and to be − 17.52 J/kg-K, − 17.33 J/kg-K and 465.7 J/kg for Er6Ni2.25Al0.75, respectively.

Spin-dependent high-order topological states and corner modes in a monolayer FeSe/GdClO heterostructure

We propose that a spin-dependent second-order topological insulator can be realized in monolayer FeSe/GdClO heterostructure, in which substrate GdClO helps to stabilize and enhance the antiferromagnetic order in FeSe. The second-order topological insulator is free from spin-orbit coupling and in-plane magnetic field. We also find that there exist two types of distinct corner modes residing in intersections of two ferromagnetic edges and two antiferromagnetic edges, respectively. The underlying physics for ferromagnetic corner mode follows a sublattice-chirality-kink picture. More interestingly, ferromagnetic corner mode shows spin-dependent property, which is also robust against spin-orbit coupling. Unexpectedly, antiferromagnetic corner mode can be taken as a typical emergent and hierarchical phenomenon from an array of ferromagnetic corner modes. Remarkably, antiferromagnetic corner modes violate general kink picture and can be understood as bound states of a one-dimensional Schrodinger equation under a connected potential well. Our findings not only provide a promising second-order topological insulator in electronic materials, but uncover some new properties of corner modes in high-order topological insulator.

Large anomalous Hall effect and intrinsic Berry curvature in magnetic Weyl semimetal NdAlGe

Weyl semimetals driven by both time-reversal (TRS) and inversion symmetries (IS) are rare and be a good platform to investigate the relationship between chiral current and magnetic order. NdAlGe compound, grown in a single crystalline form by the flux method, has a noncentrosymmetric I41md crystal structure, which breaks inversion symmetry. The magnetic susceptibility χ(T) shows anisotropic behavior; ferromagnetic with divergence of field cooling (FC) and zero field cooling (ZFC) in H∥c, and antiferromagnetic transition for magnetic field H⊥c. The band structure calculation has revealed that NdAlGe is the type-II Weyl semimetal with four types of Weyl nodes in the ab-plane with a probable Fermi surface nesting vector. The ferromagnetic spin alignment gives a significant anomalous Hall coefficient Rs and large anomalous Hall conductivity σxyA, for H∥c. The giant anomalous Hall conductivity σxyA, constant SH=σxyA/M (H = 50 kOe) value, and their Karplus and Luttinger (KL) analysis support that the giant AHE is associated with the intrinsic Berry curvature in NdAlGe compound. The intrinsic Berry curvature is also confirmed by the planar Hall effect over a wide temperature range, implying that the Weyl semimetallic property is not relevant with the magnetic order.

Enhanced multiferroicity of Ho0.95Co0.05Fe0.95Ti0.05O3 by co-doping in HoFeO3 nanoparticle system

Nanocrystalline HoFeO3 is a potential multiferroic and will be more useful if its multiferroicity can be enhanced by improving the magnetic and electric ordering. In this regard, co-doping with Co and Ti, was considered in HoFeO3 (HFO) to enhance its magneto-electric behavior and thus synthesize a new monophasic multiferroic, Ho0.95Co0.05Fe0.95Ti0.05O3 (HCFTO). Both the pristine and doped HFO nanoparticles were synthesized in sol–gel route. Rietveld analyses of X-ray diffractograms, confirmed the formation of pure orthorhombic (Pnma) phase of both bare and doped HFO. Presence of the canted antiferromagnetism of bare HFO at room-temperature with antiferromagnetic transition at ∼ 637 K was confirmed in susceptibility vs. temperature variation and by the nature of MH loops. Interestingly, substantial enhancement of magnetism was observed in HCFTO compared to that of bare one, where the room-temperature maximum magnetization is enhanced by 73%. Dielectric strength of HFO (∼48) is also enhanced highly (∼3.4 times) in HCFTO (∼165), and the loss factor is lowered to nearly half. Current density vs. electric field (J-E) curve suggests the presence of polarization at room temperature with negligible leakage loss. Lower leakage loss of HCFTO indicates better multiferroicity than HFO. Direct measurement of ferroelectric loop shows the room-temperature ferroelectricity of bare HFO (Pmax ∼ 0.0041 µc/cm2) well improved (∼1.5 times) in the doped HCFTO (Pmax ∼ 0.0061 µc/cm2) with lower hysteresis loss. Room-temperature magnetoelectric coupling measurements, shows a high value (∼2.47%) of magnetocapacitance in the doped system, which is much higher (∼4.94 times) than the bare one (∼0.5%). All these properties of the sample clearly confirm the co-doping in the HoFeO3 nanoparticle system results in a considerable improvement in its magnetoelectric behavior, and this co-doped Ho0.95Co0.05Fe0.95Ti0.05O3 system can be a promising and potential magnetoelectric multiferroic for device applications.

Proximate deconfined quantum critical point in SrCu2(BO3)2.

The deconfined quantum critical point (DQCP) represents a paradigm shift in quantum matter studies, presenting a "beyond Landau" scenario for order-order transitions. Its experimental realization, however, has remained elusive. Using high-pressure 11B nuclear magnetic resonance measurements on the quantum magnet SrCu2(BO3)2, we here demonstrate a magnetic field-induced plaquette singlet to antiferromagnetic transition above 1.8 gigapascals at a notably low temperature, Tc ≃ 0.07 kelvin. First-order signatures of the transition weaken with increasing pressure, and we observe quantum critical scaling at the highest pressure, 2.4 gigapascals. Supported by model calculations, we suggest that these observations can be explained by a proximate DQCP inducing critical quantum fluctuations and emergent O(3) symmetry of the order parameters. Our findings offer a concrete experimental platform for investigation of the DQCP.

Spin density wave and antiferromagnetic transition in EuFe2As2: a high field transport and heat capacity study

Abstract Here we reported structural, electrical, magnetic, and thermal transport properties of ternary pnictide bulk iron based compound EuFe2As2 (Eu-122). This compound (Eu-122) crystallized in ThCr2Si2-type tetragonal phase structure with space group I4/mmm at ambient temperature. A promising divalent state (Eu2+) of Eu-ions was observed in the studied EuFe2As2. Magnetic ordering of Eu2+ ions takes place at very low temperature at around T N = 20 K in EuFe2As2. The ferromagnetic interactions between Fe–Fe ions were established at higher temperature which was revealed from magnetic susceptibility measurements with negative value of the paramagnetic Curie temperature. Both magnetic phase transitions (20 K and 190 K) were clearly established the intrinsic magnetic nature revealed by both electrical transport and specific heat measurement. However the phase transition at low temperature corresponds to the magnetic ordering of Eu2+ ions while the high transition temperature is due to the itinerant moment of Fe. EuFe2As2 is the only compound among various parent compounds of iron pnictide superconductor’s family, in which both spin density wave (SDW) of Fe and A-type antiferromagnetic (AFM) ordering of the localized Eu2+ magnetic moments take place simultaneously. We observed here that the localized character of Eu anti-ferromagnetism dominated via RKKY interactions, despite the largely itinerant nature of Fe magnetic interactions. The resistivity with applied magnetic field revealed that the AFM ordering temperature of Eu2+ ions suppress with applied magnetic field. Also resistivity under hydrostatic pressure measurements shows the T SDW (Fe) transition of the Fe moments shifts towards the lower temperatures while AFM ordering of Eu2+ decreases with pressure and the same is completely disappears at 2 GPa.

Anomalous chemical pressure evolution in ThFePnN (Pn for pnictogens)

The layered compound ThFeAsN is the only member in the 1111-type iron-arsenides which exhibits superconductivity without chemical substitution or physical pressure. The unique properties of ThFeAsN were attributed to built-in chemical pressure. In this paper, we investigate the effects of iso-valent substitution of P/Sb for As in ThFePnN systems to modulate the chemical pressure. The physical properties are characterized by measuring magnetic susceptibility, electric resistivity, and specific heat. Our findings indicate that in the P-doped ThFeAs1−xPxN system, superconductivity disappears at x = 0.3, and we did not observe a second superconducting dome in the phase diagram. Instead, a possible low-temperature magnetic/charge ordering state emerges around the end member ThFePN. In the case of the Sb-doped ThFeAs1−ySbyN samples, superconductivity is gradually suppressed at y = 0.25, and the expected long-range antiferromagnetic transition does not occur thereafter. Thus, the physical properties of ThFePnN samples significantly differ from those of LaFePnO, regardless of P or Sb doping. Structural analysis reveals that the key parameters, such as the height of the pnictogens and the two-fold Fe-Pn-Fe bond angle, vary non-monotonically with doping. The inconsistency between ThFePnN and LaFePnO is discussed based on the crystal structure evolution.

Chemical pressure effects on Tm1-yRyMn0.3Co0.7O3 due to element substitution at A-site

To clarify the chemical pressure effects on TmMn0.3Co0.7O3 due to element substitution at an A-site, the crystal structure and magnetic properties of Tm1-yRyMn0.3Co0.7O3 (R = Y and Lu) were investigated. All the prepared samples possessed a perovskite-type orthorhombic structure with the Pnma space group, and the unit-cell volume V increased with the average radius of A-site ions 〈rR〉. From the effective magnetic moment Peff and M−H measurements, it was found that the electronic states of the ions in the samples were Tm3+, Mn4+, Co2+(high-spin state, S = 3/2), and Co3+(low-spin state, S = 0). The physical parameters including the canted antiferromagnetic transition temperature Tc increased with V. The field-cooled magnetization MFC below 30 K could be explained by the antiferromagnetic interaction between the paramagnetic Tm and the 3d metal sublattices. Since Tc and the fitting parameter of this two-sublattice model increased with V, these changes were considered to be attributed to the chemical pressure generated by element substitution at the A-site.

Magnetic phase diagram in the three-dimensional triangular-lattice antiferromagnet Sr3CoTa2O9 with small easy-axis anisotropy

We report the results of low-temperature magnetization and specific heat measurements of ${\mathrm{Sr}}_{3}{\mathrm{CoTa}}_{2}{\mathrm{O}}_{9}$ powder, in which ${\mathrm{Co}}^{2+}$ ions with effective spin-1/2 form a uniform triangular lattice in the $ab$ plane. It was found that ${\mathrm{Sr}}_{3}{\mathrm{CoTa}}_{2}{\mathrm{O}}_{9}$ undergoes successive antiferromagnetic transitions at ${T}_{\mathrm{N}1}=0.97\phantom{\rule{4pt}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{N}2}=0.79\phantom{\rule{4pt}{0ex}}\mathrm{K}$ at zero magnetic field. As the magnetic field increases, both ${T}_{\mathrm{N}1}$ and ${T}_{\mathrm{N}2}$ decrease monotonically. The obtained magnetic field vs temperature phase diagram together with a sharp magnetization anomaly at a saturation field of ${\ensuremath{\mu}}_{0}{H}_{\mathrm{s}}=2.3$ T indicates that ${\mathrm{Sr}}_{3}{\mathrm{CoTa}}_{2}{\mathrm{O}}_{9}$ is described as a spin-1/2 three-dimensional triangular-lattice antiferromagnet with a weak easy-axis anisotropy. We discuss the characteristics of the magnetic phase diagram, which approximates the phase diagram for the magnetic field perpendicular to the $c$ axis.

Doping-induced spin reorientation and magnetic phase diagram ofEuMn1−xZnxSb2 (0≤x≤1)

${\mathrm{EuMnSb}}_{2}$ is an intriguing magnetic topological semimetal containing two antiferromagnetic sublattices, and the interplay of magnetism between Eu and Mn sublattices leads to rich interesting transport phenomena. Here we report a comprehensive experimental study of the magnetic properties in ${\mathrm{EuMn}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{Sb}}_{2}$ (0 $\ensuremath{\le}x\ensuremath{\le}$ 1) by using structural, resistivity, magnetization, and specific heat measurements. The magnetic phase diagrams of ${\mathrm{EuMn}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{Sb}}_{2}$ along two magnetic field orientations are established based on magnetization and specific heat measurements, constituted by the antiferromagnetic ordering of Mn at high temperature, and successive magnetic transitions of Eu at low temperatures. The antiferromagnetic transition temperature of Mn is suppressed by Zn doping and cannot be detected by specific heat measurements when $x>$ 0.3. The antiferromagnetic transition temperature of Eu exhibits a weak nonmonotonic doping dependence with a significant anisotropy in the doping range of 0 $\ensuremath{\le}x\ensuremath{\le}$ 0.4. The spin orientation of Eu is gradually reoriented from the out-of-plane direction to the in-plane direction. It closely correlates with the Mn antiferromagnetic ordering, indicating a strong coupling between the Eu and Mn magnetism. Our study will be helpful for understanding the magnetic properties of compounds with two antiferromagnetic lattices and open an avenue for tuning the spin orientation through the interaction between the different magnetic lattices.

Structural and magnetic transitions in the Bi2Fe4O9/BiFeO3 composite

A Bi2Fe4O9/BiFeO3 composite with a percentage ratio of 67/33 has been synthesized, its morphological analysis has been carried out. The average crystallite sizes for each phase have been determined. The magnetization hysteresis has been established and the temperature of its disappearance has been found. Using the infrared absorption spectra, temperatures of the magnetic phase transitions in each phase have been determined from the magnetic susceptibility, magnetostriction constant, ultrasound damping coefficient, and phonon mode softening. The change of magnetostriction constant sign observed in the vicinity of the spin reorientation transition and antiferromagnetic transition in mullite has been attributed to the change of the sign of the magnetoelastic constants. The interaction between the phases in the composite and the correlation of its structural and magnetic properties have been established.