Successive Magnetic Transitions Research Articles

Inverse and conventional dual magnetocaloric effects in Ni substituted Y-type Sr2Zn2-xNixFe12O22 hexaferrites

The effects of Ni substitution on magnetic and magnetocaloric effect (MCE) are investigated in polycrystalline Y-type hexaferrites of Sr2Zn2-xNixFe12O22 (x = 0.0, 0.8, and 2.0). With the increasing of temperature, the M-T curves indicate successive magnetic structure transitions exist in Sr2Zn2-xNixFe12O22 (x = 0.0, 0.8, and 2.0), which play significant roles in MCE behaviors. As the Ni2+ doping ratio increases, the shape of −ΔSM−T curves near room temperature evolves gradually from a table-like to a peak-like form. Particularly, a significant contrast between CMCE and IMCE is observed below 100 K, whose behavior can be inherently exploited for heat sink in magnetic refrigeration applications. Among the samples in this series, Sr2Zn1.2Ni0.8Fe12O22 plays the best CMCE and IMCE performances, with the maximum magnetic entropy change (−ΔSMmax) values of 0.78 J/kg K at 354 K and −0.56 J/kg K at 16 K for ΔH=50kOe , respectively. Our work demonstrates that Sr2Zn2-xNixFe12O22 hexaferrites have great potential to be tailored for magnetic refrigeration with special needs such as different operating temperature zones, Ericsson cycle or heat sink at refrigeration.

Magnetic exchange interactions and non-Debye relaxation in spin-3/2 frustrated Kagomé magnet Co3V2O8

We report the experimental determination of the magnetic exchange parameter ( J/kB = 2.88 ± 0.02 K) for the Spin-3/2 ferromagnetic (FM) Kagomé lattice system: Co3V2O8 using the temperature dependence of dc-magnetic susceptibility χ(T) data by employing the fundamental Heisenberg linear chain model. Our results are quite consistent with the theoretically reported nearest neighbor dominant FM exchange coupling strength Jex−NN∼ 2.45 K. Five different magnetic phase transitions (6.2–11.2 K) and spin-flip transitions (9.6–7.7 kOe) have been probed using the ∂ ( χT )/ ∂T vs. T, heat capacity (CP -T) and differential isothermal magnetization curves. Among such sequence of transitions, the prominent ones being incommensurate antiferromagnetic (AFM) state at 11.2 K, commensurate AFM state at 8.8 K, and commensurate FM state across 6.2 K. All the successive magnetic phase transitions have been mapped onto a single H-T plane through which one can easily distinguish the above-mentioned different phases. The magnetic contribution of the CP -T near TN (11.2 K) has been analyzed using the power-law expression CM = A|T — TN|−α resulting in the critical exponent α = 0.18 ± 0.01 (0.15 ± 0.003) for T < TN (T > TN ), respectively for the Co3V2O8. It is interesting to note that non-Debye type dipole relaxation is quite prominent in Co3V2O8 and was evident from the Kohlrausch–Williams–Watts analysis of complex modulus and impedance spectra (0 ⩽β⩽ 1). Mott’s variable-range hopping of charge carriers process is evident through the resistivity analysis ( ρac -T −1/4 ) in the temperature range 275 ∘C–350 ∘C. Moreover, the frequency-dependent analysis of σac (ω) follows Jonscher’s power law yielding two distinct activation energies ( Ea∼ 0.37 and 2.29 eV) between the temperature range 39 ∘C–99 ∘C and 240 ∘C–321 ∘C.

J_{eff}=1/2 Hyperoctagon Lattice in Cobalt Oxalate Metal-Organic Framework.

We report the magnetic properties of a cobalt oxalate metal-organic framework featuring the hyperoctagon lattice. Our thermodynamic measurements reveal the J_{eff}=1/2 state of the high-spin Co^{2+} (3d^{7}) ion and the two successive magnetic transitions at zero field with two-stage entropy release. ^{13}C-NMR measurements reveal the absence of an internal magnetic field in the intermediate temperature phase. Multiple field-induced phases are observed before full saturation at around 40T. We argue the unique cobalt oxalate network gives rise to the Kitaev interaction and/or a bond frustration effect, providing an unconventional platform for frustrated magnetism on the hyperoctagon lattice.

Successive magnetic transitions and frustrated magnetism in Fe2(HPO3)3 ⋅ 4H2O

AbstractWe report the magnetic and optical properties of Fe2(HPO3)3 ⋅ 4H2O. By combined magnetic susceptibility and specific heat measurements, we find two antiferromagnetic (AFM) transitions (TN1=9 K, TN2=5 K) which originate from the AFM exchange interactions mediated by the (HPO3)2− anions. Compared with the non‐hydrated compound Fe2(HPO3)3, the magnetic interaction strength and ordering temperature of Fe2(HPO3)3 ⋅ 4H2O are both reduced by a factor of ~2. Through density functional theory (DFT) analysis we find almost degenerate AFM states in Fe2(HPO3)3 ⋅ 4H2O which are close in energy. The competition of these AFM states might lead to the two successive AFM phase transitions at low temperature. The low ordering temperature as well as competing AFM states both imply frustrated magnetism in Fe2(HPO3)3 ⋅ 4H2O, probably originating from the complex competing AFM interactions. The optical properties of Fe2(HPO3)3 ⋅ 4H2O are also investigated by photoluminescence and infrared spectroscopies.

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

Successive magnetic transitions and magnetocaloric effects in intermetallic compounds RE5Pt3 (RE = Dy, Ho)

The structure, low-temperature magnetic transition behaviors, and magnetocaloric properties of rare-earth-based binary compounds RE5Pt3 (RE = Dy, Ho) were studied. Both of the compounds crystallize in the Mn5Si3 hexagonal structure with a P63/mcm space group. With the decrease of temperature, the compounds undergo a phase transition from the paramagnetic (PM) state to the ferromagnetic (FM) state, followed by a spin reorientation. In the paramagnetic region, the reciprocal magnetic susceptibilities of RE5Pt3 obey the Curie-Weiss law. The effective paramagnetic magnetic moment values were determined to be 10.59 μB/Dy3+ and 10.40 μB/Ho3+, respectively, with the corresponding paramagnetic Curie temperatures of 30.0 K and 16.4 K. The maximum magnetic entropy changes (-ΔSM) of RE5Pt3 (RE = Dy, Ho) were calculated to be 8.2 J/kg K and 9.1 J/kg K for a field change of 0–5 T. In addition, it is confirmed that the successive magnetic phase transition enlarges the magnetic entropy change and the working temperature region by Lorentz bimodal fitting. Evidently, the RE5Pt3 (RE = Dy, Ho) compounds with reversible MC effect are expected to have effective applications in the low-temperature range.

Enhanced magnetocaloric effect accompanying successive magnetic transitions in TbMn2Si2-xGex compounds

The lack of magnetic refrigeration (MR) materials with high magnetocaloric effect (MCE) and large relative cooling power (RCP) in the temperature range required for hydrogen liquefaction (20 K–77 K) is a bottleneck for practical applications of MR cooling systems. The present investigation of TbMn2Si2-xGex compounds (x = 0.1, 0.2) by variable temperature neutron and synchrotron X-ray diffraction, magnetization and heat capacity measurements, establish that substitution of Si with Ge in TbMn2Si2 leads to a significant enlargement of the unit cell and modification of the magnetic properties. Two consecutive ferromagnetic first-order transitions occur below 77 K with the third transition from paramagnetism to a collinear antiferromagnetic state being determined around 500 K. The resultant plateau-like MCE with large RCP below 77 K in these designed compounds offers scope for application for hydrogen liquefaction. Detailed neutron investigation confirm that four magnetic states exist within the temperature range 5 K to 500 K, with two successive first-order magnetic transitions below 77 K responsible for the large MCE. Our specific heat studies provide evidence of strong contributions from the nuclear specific heat and the corresponding nuclear specific heat coefficients of A = 430 ± 50 mJ mol−1 K and A = 418 ± 60 mJ mol−1 K have been determined for TbMn2Si2-xGex with x = 0.1 and x = 0.2, respectively. The overlapping entropy curves near these successive transitions lead to a plateau-like magnetothermal effect as well as a large reversible MCE for both samples (e.g. ΔSMmax = 14.0 J/kg K and ΔTmax = 7.6 K; RCP = 379 J/kg for TbMn2Si1.9Ge0.1 for an applied field of 5 T) indicating that the material can operate over a wide temperature range – particularly for hydrogen liquefaction.

Wolframite-type MnMoO4: Magnetization, sintering by Cool-SPS, and magnetodielectric effect

Dense ceramic samples of wolframite-type MnMoO4 (w-MnMoO4) have been prepared by Cool-SPS (Spark Plasma Sintering) for the first time with the goal of investigating the magnetic, dielectric, and magneto-electric properties of this thermally fragile polymorph of MnMoO4. Earlier studies found that w-MnMoO4 converts to the structurally different α-MnMoO4 phase if heated in air at 873 K, thus hindering fabrication of w-MnMoO4 ceramics by conventional high-temperature sintering. Unsintered powder samples, which were prepared via a hydrothermal method, and dense ceramics elaborated by Cool-SPS have the same magnetic properties. Magnetic susceptibilities display Curie-Weiss behaviour, χ = C/(T-θ), with effective moments for Mn2+ ion μeff ≈ 5.9 μB/Mn-atom and negative Weiss temperatures θ ≈ - 96 to - 98 K. Unlike the isostructural multiferroic compounds MnW1-xMoxO4 (0 ≤ x < 0.3) which exhibits at least two successive magnetic transitions below 15 K, w-MnMoO4 undergoes only one paramagnetic-to-antiferromagnetic transition at TN ≈ 32 K. The field-dependent magnetization at 2 K shows a spin-flop transition at μ0HSF ≈ 2 T. Capacitance and dielectric losses obtained for a ceramic between 2 and 300 K in zero field and in a field of 9 T reveal several weak anomalies. Dielectric anomalies are observed at the magnetic phase transition, suggesting a magnetoelectric coupling. Qualitatively different dielectric and magnetodielectric behaviours occur in α-MnMoO4 ceramics at low temperature.

Magnetic and magnetocaloric properties of Tb1.4Dy0.6In compound

This work summarizes the magnetic, thermal, magnetocaloric, and electrical transport properties of Tb1.4Dy0.6In and its critical behavior. First, we find that 60% Dy at the 2d (1/3, 2/3, 3/4) lattice sites of Tb2In (hexagonal Ni2In -type (space group- P63/mmc (No. 194))) leads to the formation of Tb1.4Dy0.6In, which undergoes a ferromagnetic transition at 155 K (T1) followed by an antiferromagnetic transition around 75 K (T2). Successive second-order magnetic transitions at T1 and T2 demonstrate a table-like hysteresis-free magnetocaloric effect around natural gas's liquefaction temperature (55–196 K). To understand the efficiency of Tb1.4Dy0.6In as a coolant, various cooling figures of merits such as isothermal entropy change, adiabatic temperature change, relative cooling power, the temperature averaged entropy change, and coefficient of refrigerant performance were determined. Along with the studies of magnetic properties, the critical exponent analysis endorses mean–field model that concord with the indirect long-range RKKY interaction between the rare-earth atoms in Tb1.4Dy0.6In. Furthermore, first-principle calculations indicate that the most hybridized dp states lie below the Fermi energy level and support the second-order magnetic nature of the transition. Overall, this study provides insights into the magnetocaloric properties of Dy-doped Tb2In and highlights its potential as an efficient coolant.

Synthesis, structure and properties of RNiBN (R = rare-earth elements)

We report the structural and physical properties of new nitridoborates RNiBN (R = Nd, Sm, Gd, Tb, Dy, Ho, and Er). These compounds crystallize in a tetragonal LaNiBN-type structure with two-dimensional Ni2B2 and RN layers. The physical properties measurements indicate that they are antiferromagnetic metals. For R = Gd and Ho, a successive magnetic transition was observed below N é el temperature, possibly associated with spin re-orientation due to Ruderman-Kittel-Kasuya-Yosida interaction. A giant magnetocaloric effect was measured in the R = Er and Ho compounds, which is related to a field-induced first-order metamagnetic transition from antiferromagnetic to ferromagnetic state. Our results indicate that RNiBN (R = Er and Ho) may be promising candidates for low temperature magnetic refrigeration

Large table-like magnetocaloric effect in boron-doped Er5Si3B0.5 compound

In this work, Er5Si3B0.5 compound with the Mn5Si3-type hexagonal structure was synthesized, and the structure, magnetic properties, and the magnetocaloric effect were investigated theoretically and experimentally. The magnetic measurement results show a complex successive magnetic transition below TN. However, the magnetization of the Er5Si3B0.5 compound below TN is saturated under lower magnetic field relative to the Er5Si3 compound. Theoretical calculation indicates that this was attributed to the enhanced inter-orbital exchange interaction after doping B element. The complicated successive magnetic transitions contribute to the table-like magnetocaloric effect observed in the Er5Si3B0.5 compound with a wide temperature region. The maximum magnetic entropy change and the temperature averaged entropy change (30) are 10.1 and 9.02 J/kg K for the Er5Si3B0.5 compound under varying magnetic fields from 0 to 5 T, respectively. The temperature averaged entropy change (30) is reduced by just 11% compared to the maximum magnetic entropy change. While presenting an ideal magnetic refrigeration material with a large table-like magnetocaloric effect for hydrogen liquefaction, our work also demonstrates the feasibility of regulating magnetic behavior through enhanced orbital exchange interactions to develop magnetic refrigeration materials with outstanding performance.

Structure, magnetism and magnetocaloric effects in Er5Si3B x (x = 0.3,0.6) compounds

We investigate the structure, magnetic properties, magnetic phase transitions and magnetocaloric effects (MCEs) of Er5Si3B x (x = 0.3, 0.6) compounds. The Er5Si3B x (x = 0.3, 0.6) compounds crystalize in a Mn5Si3 type hexagonal structure (space group: P63/cm) and exhibit a successive complicated magnetic phase transition. The extensive magnetic phase transitions contribute to the broad temperature range of MCEs exhibiting in Er5Si3B x (x = 0.3, 0.6) compounds, with maximum magnetic entropy change () and refrigeration capacity of 10.2 J⋅kg−1⋅K−1, 356.3 J/kg and 11.5 J⋅kg−1⋅K−1, 393.3 J/kg under varying magnetic fields 0–5 T, respectively. Remarkably, the δT FWHM values (the temperature range corresponding to ) of Er5Si3B x (x = 0.3, 0.6) compounds were up to 41.8 K and 39.6 K, respectively. Thus, the present work provides a potential magnetic refrigeration material with a broad temperature range MCEs for applications in cryogenic magnetic refrigerators.

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 $x&gt;$ 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.

Cycloidal spiral magnetic structures in the spin-chain compounds BaRFeO4 ( R=Yb and Tm): Ordered Yb versus partly ordered Tm

$\mathrm{Ba}R\mathrm{Fe}{\mathrm{O}}_{4}$ compounds containing magnetic rare-earth ions ($R=\mathrm{Yb}$, Tm) were prepared by a conventional solid-state method in air. We present detailed measurements of magnetic properties (specific heat, magnetic susceptibility) to demonstrate the presence of three successive magnetic phase transitions (at ${T}_{\mathrm{N}1}$, ${T}_{\mathrm{N}2}$, and ${T}_{3}$) in both compounds and employed neutron diffraction to determine the magnetic structures. Both compounds are isostructural (orthorhombic space group $Pnma$) and magnetic ions form rings and chains along the $b$ direction. All magnetic structures are incommensurate with a propagation vector $\mathbf{k}=(0,\phantom{\rule{0.28em}{0ex}}0,\phantom{\rule{0.28em}{0ex}}{k}_{z})$. Magnetic ordering of ${\mathrm{Fe}}^{3+}$ ions occurs at ${T}_{\mathrm{N}1}$ and ${T}_{\mathrm{N}2}$, where two different irreducible representations (irreps) order. Below ${T}_{\mathrm{N}1}$, there is a collinear spin-density wave with ordered ${\mathrm{Fe}}^{3+}$ moments along the chain direction ($b$ axis). Below ${T}_{\mathrm{N}2}$, this component remains stable and an additional component inside the $ac$ plane appears. Each Fe chain adopts a collinear antiferromagnetic structure with a constant magnetic phase. The two Fe rings in the unit cell have a different chirality and a noncollinear coupling. The mixing of two irreps leads to a cycloidal spiral magnetic structure that allows spin-induced ferroelectric polarization at ${T}_{\mathrm{N}2}$. With the presence of modulated components both perpendicular and along the propagation vector $\mathbf{k}$, the magnetic structure can be viewed as a sum of a helix and a cycloid structure. For ${\mathrm{BaTmFeO}}_{4}$, the magnetic structure has a larger cycloidal contribution and the dielectric constant \ensuremath{\epsilon} exhibits a small peak at ${T}_{\mathrm{N}2}$. ${\mathrm{Yb}}^{3+}$ moments order at ${T}_{3}$ with each Yb chain having a constant magnetic phase and a collinear antiferromagnetic structure stabilized by $4f\ensuremath{-}4f$ electron-exchange interactions. In contrast, no constant magnetic phase is observed at the Tm chains. Below ${T}_{3}$, magnetic order of Tm2 ions is induced by $3d\ensuremath{-}4f$ electron-exchange interactions and Tm1 ions remain disordered down to the lowest measured temperature $T=1.6\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ due to frustration of magnetic exchange interactions. The obtained magnetic structures are compared with those of ${\mathrm{BaYFeO}}_{4}$.

Electronic signatures of successive itinerant, antiferromagnetic transitions in hexagonal La2Ni7

We use high-resolution angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations to study the electronic and magnetic properties of La2Ni7, an itinerant magnetic system with a series of three magnetic transition temperatures upon cooling, which end in a weak antiferromagnetic ground state. Our APRES data reveal several electron and hole pockets that have hexagonal symmetry near the Γ point. We observe significant reconstruction of the band structure upon successive magnetic transitions at T 1 ∼ 61 K, T 2 ∼ 57 K and T 3 ∼ 42 K. Several features observed in ARPES data were reasonably well reproduced by DFT calculations, while others were not. In particular, the flat band near E F predicted by DFT in antiferromagnet (AFM) state, was seemingly absent in ARPES data. Our results detail the effects of magnetic ordering on the electronic structure in a Ni-based weak AFM and highlight challenges of current computational methods.

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.

Polyhedral Distortions and Unusual Magnetic Order in Spinel FeMn2O4.

Spinel compounds AB2X4 consist of both tetrahedral (AX4) and octahedral (BX6) environments with the former forming a diamond lattice and the latter a geometrically frustrated pyrochlore lattice. Exploring the fascinating physical properties and their correlations with structural features is critical in understanding these materials. FeMn2O4 has been reported to exhibit one structural transition and two successive magnetic transitions. Here, we report the polyhedral distortions and their correlations to the structural and two magnetic transitions in FeMn2O4 by employing the high-resolution neutron powder diffraction. The cation distribution is found to be (Mn0.92+Fe0.13+)A(Mn3+Fe0.93+Mn0.12+)BO4. While large trigonal distortion is found even in the high-temperature cubic phase, the first-order cubic-tetragonal structural transition associated with the elongation of both tetrahedra and octahedra with shared oxygen atoms along the c axis occurs at TS ≈ 750 K, driven by the Jahn-Teller effect of the orbital active B-site Mn3+ cation. Strong magnetoelastic coupling is unveiled at TN1 ≈ 400 K as manifested by the appearance of Néel-type collinear ferrimagnetic order, an anomaly in both tetrahedral and octahedral distortions, as well as an anomalous decrease of the lattice constants c and a weak anomaly of a. Upon cooling to TN2 ≈ 65 K, it evolves to a noncollinear ferrimagnetic order accompanied by the different moments at the split magnetic sites B1 and B2. Only one-half of the B-site Mn3+/Fe3+ spins, i.e., the B2-site spins in the pyrochlore lattice, are canted, which is a unique magnetic order among spinels. The canting angle between A-site and B2-site moments is ∼25°, but the B1-site moment stays antiparallel to the A-site moment even at 10 K. This noncollinear order is accompanied by a modification of the O-B-O bond angles in the octahedra without significant change in lattice constants or tetrahedral/octahedral distortion parameters, indicating a distinct magnetoelastic coupling. We demonstrate distinct roles of the A-site and B-site magnetic cations in the structural and magnetic properties of FeMn2O4. Our study indicates that FeMn2O4 is a wonderful platform to unveil interesting magnetic order and to investigate their correlations with polyhedral distortions and lattice.

Investigation of crystal structure and magnetic properties in magnetic composite of soft magnetic alloy and hard magnetic ferrite

The structural and magnetic properties have been investigated in the magnetic composites of hard magnetic Barium hexaferrite (BHF) and soft magnetic Ni–Mn–Sn Heusler alloy. The magnetic composites undergo two distinct ferromagnetic to paramagnetic and ferrimagnetic to paramagnetic phase transitions corresponding to alloy and BHF phases, respectively. Magnetic biasing between the hard and soft magnetic phases has been observed in the composites when both the phases are in the ferromagnetic ordering i.e., a squeezing in the magnetic hysteresis curve is observed around H = 0. The squeezing effect may be used in the magnetic memory device application where an optimum coercivity, high remanent magnetization, and high squareness ratio are required. On the other hand, the composites show high magnetocaloric effect with a constant high value of magnetic entropy changes between the two successive magnetic transitions. This gives an advantage with wide working temperature in the magnetocaloric application.

A cascade of magnetic phase transitions and a 1/3-magnetization plateau in selenite-selenate Co3(SeO3)(SeO4)(OH)2 with kagomé-like Co2+ ion layer arrangements: the importance of identifying a correct spin lattice.

We prepared a new compound, Co3(SeO3)(SeO4)(OH)2, having layers in a kagomé-like arrangement of Co2+ (spin S = 3/2) ions. This phase crystallizes in the orthorhombic space group Pnma (62) with unit cell parameters a = 11.225(9) Å, b = 6.466(7) Å and c = 11.530(20) Å. Its layers, parallel to the ab-plane, are made up of Co1O5 square pyramids and Co2O6 and Co3O6 octahedra. As the temperature is lowered, Co3(SeO3)(SeO4)(OH)2 undergoes three successive magnetic transitions at 27.5, 19.4 and 8.1 K, and the magnetization of Co3(SeO3)(SeO4)(OH)2 measured at 2.4 K exhibits a 1/3-magnetization plateau between 7.8 and 19.9 T. TheH-Tmagnetic phase diagram constructed for Co3(SeO3)(SeO4)(OH)2from ac and dc magnetic susceptibility, specific heat and magnetization measurements contains three magnetic phases I, II and III. Phase I is antiferromagnetic, while phases II and III are ferrimagnetic and responsible for the 1/3-magnetization plateau. To interpret these complex magnetic properties, we identified the correct spin lattice for Co3(SeO3)(SeO4)(OH)2 by evaluating its intralayer and interlayer spin exchanges based on spin-polarized DFT+U calculations.

Influence of Ga-substitution to the structural and magnetic properties of (Mn,Fe)-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- bixbyite

To study the dependence of the properties of ternary oxides (Mn,Fe,Ga)2O3 with the bixbyite structure on the composition, the temperature dependences of the magnetization and ac magnetic susceptibility of two single-crystal samples of different compositions obtained using the flux method were analyzed. A detailed study of the structure was carried out using single-crystal X-ray diffraction analysis, and the changes in structural parameters depending on the composition were analyzed. The dc magnetization and ac magnetic susceptibility of Fe1.1Mn0.76Ga0.14O3 and Fe0.65Mn1.1Ga0.26O3 bixbyites have been studied. Despite the qualitatively similar behavior of the magnetic properties, significant differences were also found, despite a small difference in the Mn/Fe/Ga ratio in the samples under study. It is shown that both compounds experience two successive low-temperature magnetic phase transitions from the paramagnetic phase at T=20-32 K as the temperature is lowered. Calculations of the Mydosh parameter for the detected phase transitions showed different degrees of ordering in the compounds under study. Keywords: transition metal oxides, magnetic phase transitions, spin glass state, bixbyite.