Small Magnetic Hysteresis Research Articles

Effect of synthesis method on structural and magnetic properties of La0.7Ca0.2Ba0.1MnO3

Abstract We study the effect of the synthesis method on the structural and magnetic properties of La0.7Ca0.2Ba0.1Mn03. The samples were synthesized by coprecipitation and solution combustion methods. X-ray diffraction and scanning electron microscopy were performed to investigate the crystallographic structure, showing that both methods produced La0.7Ca0.2Ba0.1Mn03 monophasic samples. From magnetization measurements a second-order, ferromagnetic to paramagnetic, phase transition was observed. The Curie temperature is found to be 272 K for the sample obtained by coprecipitation and 283 K for the sample obtained by solution combustion. There is a small magnetic hysteresis for both samples. The magnetocaloric parameters were obtained using a phenomenological model; the magnetic entropy change and relative cooling power factor are higher in the sample synthesized by combustion.

Magnetic and electrical properties of Co2Te3 single crystal

The Co-Te system has become a prominent field of research in recent times. CoTe2 is confirmed to be a Dirac semimetal, while Co2Te is predicted to host the quantum anomalous Hall effect. Here, we have successfully grown high-quality Co2Te3 single crystals using the solid-state reaction method and have characterized them using the energy dispersive X-ray spectroscopy, the X-ray diffraction and Laue diffraction. The X-ray rocking curve with a full-width at half-maximum of 0.067° shows Co2Te3 single crystals have good crystalline quality and mosaicity. Co2Te3 single crystals possess a hexagonal structure with the space group of P63/mmc. Resistivity measurements reveal typical metallic behavior with a transition from Non-Fermi liquid to low-temperature Landau Fermi-liquid behavior around 50 K, which can be fitted by the parallel resistance model. Magnetic measurements show no obvious anisotropy between the in-plane and out-of-plane directions with the presence of a small magnetic hysteresis at 1.8 K. Furthermore, Co2Te3 single crystals undergo a magnetic phase transition around 50 K and an antiferromagnetic transition modulated by the magnetic field below 8 K.

Tuning martensitic transformation and magnetocaloric effect with Bi substitution in MnCo1-xBixGe alloys

In this work, the substitution of Bi for Co atoms in MnCo1-xBixGe (x = 0.01, 0.02, 0.04, 0.06, 0.08, 0.1) alloys was prepared. The crystal structure, magnetic properties, and magnetocaloric effect have been analyzed. By tuning the Bi-content in MnCoGe alloys, the reduction of martensitic transformation (MT) temperature and the presence of a first-order magnetostructural transition (MST) were observed. Magnetic field-induced MT indicates that the magnetic field is much harder to drive MT compared to the temperature. With the Bi-content for 0.01 ≤ x ≤ 0.06, orthorhombic-type phase and hexagonal-type phase coexist. Furthermore, we observed an increase in the fraction of the hexagonal-type phase and a corresponding decrease in the fraction of the orthorhombic-type phase. It is beneficial to the refrigeration capacity for the isothermal magnetization curves M(H) on magnetization and demagnetization procedures with small magnetic hysteresis loss. With a magnetic field of 5 T, magnetocaloric effect (MCE) can be observed involving magnetic entropy change (-ΔSM) of 26.42 J kg−1 K−1 for x = 0.06 and refrigeration capacity (RC) of 259.78 J kg−1 for x = 0.01. Thus, this material is considered a fabulous candidate for magnetic refrigeration cooling applications at room temperature.

Enhanced magnetocaloric properties and reduced annealing time of off-stoichiometric La1.2Fe11.6Si1.4B0.75 melt-spun ribbons

The off-stoichiometric La1.2Fe11.6Si1.4B0.75 alloys with different solidification rate were prepared by the arc-melting and melt-spinning methods, and the microstructure, magnetic and magnetocaloric properties of the annealed samples were investigated. It is found that the extra La and refined microstructure (induced by rapid cooling technique) shortened the annealing time to 30 min at 1273 K. The B atoms partially dissolved in lattice interstice of 1:13 phase and brings about the lattice expansion, which improves the TC and enhances the MCE of the La1.2Fe11.6Si1.4B0.75 alloy. The high cooling rate contributes to the depression of thermal and magnetic hysteresis. In the annealed La1.2Fe11.6Si1.4B0.75 ribbon with wheel speed of 10 m/s, the mass fraction of 1:13 phase is 86.8 wt%, and a large maximum magnetic entropy change of 20.2 J·kg−1K−1 with small thermal and magnetic hysteresis can be obtained at 193 K under field change of 2 T.

Effect of annealing on microstructure and magnetocaloric properties of plastically deformed La0.7Ce0.3Fe13.68Mn0.2Si1.4 alloys

In this study, we have employed a near-net-shape hot forging deformation with ∼67% reduction ratio, and an annealing process at 1223–1423 K to prepare bulk La0.7Ce0.3Fe13.68Mn0.2Si1.4 alloys. The deformed samples are featured by a unique microstructure consisting of layered α-Fe and La-rich phases. These layered phases gradually degrade during the subsequent annealing, and eventually appear as the magnetocaloric phase (the 1:13 phase) matrix embedded mainly with the α-Fe particles. Upon annealing at 1323 K, the deformed sample has the largest 1:13 phase formation rate. Significant magnetic entropy change of 15.6 J/kg K and a relatively small magnetic hysteresis of 30.9 J/kg at 5 T are achieved in the current forged La-Ce-Fe-Mn-Si alloy on an optimal annealing condition, i.e., 1323 K for 24 h. The large magnetic entropy, rapid 1:13 phase formation rate and near-net shape make the hot-forged La-Ce-Fe-Mn-Si alloys promising magnetic refrigerants.

Room-Temperature Ferromagnetism in Mg1-xMn2+xAs2 with Layered Structure.

A series of Mg/Mn mixed intermetallic compounds Mg1-xMn2+xAs2 (x = 0.17, 0.48, 0.69) were synthesized by using metal flux reactions. Single-crystal X-ray diffraction measurements indicated that CaAl2Si2-type phases with Mn and Mg atoms located on the cation sites (Wickoff site: 1a) were obtained. The special structure of these Mg1-xMn2+xAs2 compounds corresponded to unique magnetic behavior, which led to increased divergence between zero-field-cooling (ZFC) and field-cooling magnetic susceptibilities with decreasing temperature. The small magnetic hysteresis loop measured at 300 K for Mg0.31(2)Mn2.69As2 revealed its room-temperature ferromagnetism, and its ZFC exchange bias behavior at low temperatures indicated the existence of both ferromagnetic (FM) and antiferromagnetic (AFM) interactions. Spin-polarized density functional theory calculations were also performed to verify the magnetic ground state, and these were consistent with the experimental results.

Spin-up conversion, exchange-interactions, and tailored magnetic properties in core-shell La2NiMnO6 of small crystallites

La2NiMnO6—a ferromagnetic (FM) insulator offers tunable charge carriers and spins useful to devise its multiple properties and applications. In this view, we studied a core-shell La2NiMnO6 (2–3 nm shell on 65 – 80 nm core) of a Ni2+/Ni3+(d7) to Mn4+/Mn3+ (d4) spin-up conversion— revived a new FM phase-2, raising a spin-density σ s = 0.7 s a− 1 over the Ni2+/Mn4+ species (phase-1), σ s = 0.5 s a− 1, i.e. 2.12 μB /f.u. larger spin moment. HRTEM images studied with x-ray diffraction characterizing core-shell structure that plays a crucial role in tuning the high spin FM phase-2 of profound properties. Below 110 K, the dc magnetization and ac magnetic susceptibility χ(ω, T) reveal a metastable magnetic behavior on an antiferromagnetic canting of a spin-glass nature. The results follow a Vogel–Fulcher type relaxation with a relaxation time τ 0 ∼ 10−13 s, confirming a spin-glass freezing behavior. Uniquely, FM field of phase-1 controls magnetics of phase 2 of a coupled magnet, modulating joint features with small thermal magnetic hysteresis on heating-cooling cycles.

Direct evidence of ferromagnetism in MnSb2Te4

We report the magnetic imaging of ferromagnetic domains in the van der Waals single crystal MnSb2Te4 from two different sources using cryogenic magnetic force microscopy. The magnetic field dependence of the domains reveals very weak pinning of domain walls in MnSb2Te4, resulting in a negligibly small magnetic hysteresis loop. The temperature dependence of the domain contrast reveals a mean field like behavior, in good agreement with that of bulk magnetization measurements.

Observation of table-like magnetocaloric effect and large refrigerant capacity in Nd6Fe13Pd1–xCux compounds

The table-like magnetocaloric effect is significant for the magnetic refrigeration applications above 20 K based on the Ericsson cycle. Herein, we prepared a series of Nd6Fe13Pd1–xCux (x = 0.05, 0.1, 0.15) compounds by the arc-melting method. These compounds show the single crystalline phase in the tetragonal Nd6Fe13Si-type structure with the space group I4/mcm. A magnetic phase transition from ferromagnetism to antiferromagnetism and a metamagnetic transition from the antiferromagnetic state to the ferromagnetic state are observed in each of the compounds. The compounds exhibit table-like magnetocaloric effects with large refrigerant capacities. A constant ΔSM in a temperature span of 40 K in the Nd6Fe13Pd0.85Cu0.15 compound are observed. For a field change of 0–5 T, the peak values of –ΔSM for the Nd6Fe13Pd0.95Cu0.05, Nd6Fe13Pd0.90Cu0.10, and Nd6Fe13Pd0.85Cu0.15 compounds are estimated to be 4.8, 4.6 and 4.4 J/(kg·K) with corresponding refrigerant capacity values of 323, 331 and 316 J/kg, respectively. The obtained table-like magnetocaloric effects with large refrigerant capacities as well as fairly small thermal and magnetic hysteresis deem these series of compounds good candidates for single-phase magnetic refrigeration based on the Ericsson cycle.

Microstructure and magnetocaloric properties in melt-spun and high-pressure hydrogenated La0.5Pr0.5Fe11.4Si1.6 ribbons* *Project supported by the National Natural Science Foundation of China (Grant No. 51771197), the Fund from the Chinese Academy of Sciences (Grant No. KJZD-EW-M05), and the Liaoning Revitalization Talents Program, China (Grant No. XLYC1807122).

The effects of wheel speeds and high-pressure hydrogen treatment on phase evolution, microstructure, and magnetocaloric properties in La0.5Pr0.5Fe11.4Si1.6 melt-spun ribbons are studied in this work. The results reveal that the increase of wheel speed is beneficial to the formation of cubic NaZn13-type phase and the grain refinement. The optimized wheel speed for microstructural and magnetocaloric properties is 30 m/s. The largest entropy change of 18.1 J/kg⋅K at 190 K under a magnetic field change of 0 T–5 T is obtained in La0.5Pr0.5Fe11.4Si1.6 ribbons melt-spun at 30 m/s. After a high-pressure hydrogen treatment of 50 MPa, the Curie temperature of the ribbons prepared at 30 m/s is adjusted to about 314 K and the large –ΔS M of 17.9 J/kg⋅K under a magnetic field change of 0 T–5 T is achieved at room temperature with almost none hysteresis loss. The small thermal and magnetic hysteresis and the large –ΔS M make the La0.5Pr0.5Fe11.4Si1.6 hydride ribbons appropriate for magnetic refrigerant applications around room temperature.

Large magnetocaloric effect in rapidly quenched Mn50− x Co x Ni40In10 nanomaterials

The effect of Co addition on magnetic hysteresis, martensitic transformation temperature, and magnetic entropy change of rapidly-quenched Mn50−x Co x Ni40In10 alloy nanomaterials has been investigated. The melt-spun Mn50Ni40In10 sample exhibits a small magnetic hysteresis which is further reduced by Co doping as measured between 0 and 2 T. The martensitic transformation temperature increases linearly with the electron concentration in the alloy from 195 K for Mn50Ni40In10 to 378 K for Mn45Co5Ni40In10. The Mn47Co3Ni40In10 alloy, which has phase-transition temperature close to room temperature, exhibits a substantial peak entropy change of 29.7 J kg−1 K−1 at magnetic field change of 2 T. Our results demonstrate that Mn47Co3Ni40In10 nanomaterial exhibits promising magnetocaloric properties for near-room-temperature magnetic refrigeration.

Influence of Mn substitution on crystal structure and magnetic properties of Y2Zr1-xTi1-xMn2xO7 (x = 0.0, 0.05, 0.10) family of pyrochlore oxides

The present paper deals with the effect of Mn doping on structural and magnetic properties of Y2Zr1-xTi1-xMn2xO7 (x = 0.0, 0.05, 0.10) compounds. All the samples are single phase and crystallize in the cubic system with Fd-3m space group. Both lattice parameter a and cell volume V decrease with Mn substitution because of the smaller ionic radius of Mn4+ than Zr4+ and Ti4+. No significant differences between zero field-cooled (ZFC) and field-cooled (FC) curves are evident, demonstrating that the samples exhibit no magnetic ordering or spin glass-like transition. Both the Mn-doped phases exhibit antiferromagnetic behavior, which may possibly be due to the presence of super-exchange (SE) Mn4+–O2−–Mn4+ interactions. Small magnetic hysteresis loops are observed for the Mn-doped phases suggesting the presence of weak ferromagnetic interactions.

Evolution of Crystal Structure and Magnetic Properties of Y2Zr2−xMnxO7 (x = 0.0, 0.1, 0.2) Family of Pyrochlore Oxides

The present article reviews the structural and magnetic properties of Y2Zr2−xMnxO7 compounds with respect to the extent of Mn doping. All the samples are single phase and crystallize in the cubic system with Fd-3m space group. The stability of the pyrochlore structure was established by Rietveld structural refinements. The lattice parameter and cell volume decrease with Mn substitution because of the smaller ionic radius of Mn4+ than Zr4+. The zero field-cooled (ZFC) and field-cooled (FC) curves for Mn-doped samples diverge at low temperature which is possibly due to spin-glass transition. Both the Mn-doped phases exhibit anti-ferromagnetic behavior, which could be due to the presence of super-exchange (SE) Mn4+–O2−–Mn4+ interactions. Moreover, small magnetic hysteresis loops are observed for the Mn-doped phases suggesting the presence of weak ferromagnetic interactions.

Magnetic Properties and Magnetocaloric Effect of Binary Compound NdPd

The crystal structure, magnetic and magnetocaloric properties of the binary NdPd compound were investigated by X-ray diffraction and the physical property measurement system in detail. The NdPd compound with a CrB structure exhibits a second-order magnetic phase transition from ferromagnetic to paramagnetic states at the Curie temperature TC = 15.5 K. For a magnetic field change of 0–5 T, the peak value of magnetic entropy change (− ΔSM) is evaluated to be 12.2 J/kg K, and the corresponding refrigerant capacity (RC) reaches its maximal value of 94 J/kg. The relatively small thermal hysteresis and magnetic hysteresis with the considerable magnetocaloric effect indicate that NdPd is an anticipated material for the low-temperature magnetic refrigeration.

Structural evolution and magnetic properties of high-entropy CuCrFeTiNi alloys prepared by high-energy ball milling and spark plasma sintering

A powder of equiatomic CuCrFeTiNi high-entropy alloy (HEA) was prepared by short-term (30 min) high-energy ball milling (HEBM). Our structural and chemical analysis showed that micron sized particles of bcc CuCrFeTiNi consisting of nanosized crystalline grains (∼6 nm) could be obtained after 30 min of HEBM. The influence of milling time (30 ÷ 240 min) on structural and magnetic transformations of CuCrFeTiNi powder mixture was investigated. The HEA powders were thermally stable up to 500°С based on DSC results. The HEA powder was subsequently consolidated by spark plasma sintering at 700 °C resulting in a consolidated bulk HEA with co-existing bcc and fcc phases. The as-milled CuCrFeTiNi powder blend contained a solid solution with bcc (Im3m) structure. Annealing at 600°С (t = 180 min) increased the crystallinity of the α-phase (bcc) and gave rise to formation of the γ-phase (fcc, Fm3m) whose amount grew with increasing dwell time. Between 800 and 1000°С, a tetragonal intermetallic σ-phase – most likely FeCr - appeared and subsequently vanished. At 1000°С, the final product was found to contain two solid solutions based on the γ-phase (fcc). The Vickers hardness HvHEBM = 7.7 GPa of the SPS consolidated CuCrFeTiNi alloy (milled for t = 180 min) was markedly higher than the one of SPS-produced ones without HEBM (Hv = 2.1 GPa). Paramagnetic behavior at room temperature with a small ferromagnetic contribution at low fields was observed for as-milled powder after 180 min of HEBM. A small magnetic hysteresis was observed at 5 K and 300 K with a coercive field of around 16 kA/m. Above 100 K, the inverse susceptibility of a HEA powder ball-milled for t = 240 min showed a clear paramagnetic response. The Curie temperature TC ∼50 K was found.

The effect of Sb doping for Mn on structure, magnetic properties and magnetocaloric effect of Mn1−xSbxCoGe alloys

The effect of Sb doping on the structure, magnetic properties and magnetocaloric effect of Mn1−xSbxCoGe (x = 0, 0.01, 0.02, 0.04, 0.06) alloys have been investigated. The doping of Sb for Mn results in the decrease of the structural transition temperature (Tt). For compound with x ≤ 0.01, the coupling of the magnetic and structural transitions occurs, leading to so called first-order magnetostructural transition (MST). Continually increasing x to 0.02 leads to decoupling of the magnetic and structural transitions. For $$x \geqslant 0.04$$ , an interesting phenomenon is appearance of single transition with ferromagnetic transition temperature (TC). For Mn0.99Sb0.01CoGe sample, the maximal value of the magnetic entropy change $$(\left| {\Delta {S_{\text{M}}}} \right|)$$ attains about $$17.7\,{\text{J}}/{\text{kg}}\,{\text{K}}$$ , and the refrigerant capacity (RC) can reach about 204 J/kg under a field change of 5 T. The small magnetic hysteresis, and large RC with MST near room temperature would make this alloy system prospectively put into use for room-temperature magnetic refrigeration materials.

Observation of Room-Temperature Range Magnetocaloric Effect in PrSr1−xPbxMn2O6 (0.4 ≤ x ≤ 0.6) Double-Perovskite Manganite System

The Pr(Sr1−xPbx)Mn2O6 (0.4 ≤ x ≤ 0.6) double-perovskite manganite samples have been produced by using a sol-gel method. The Rietveld refinement method has been used to analyse the structural properties, and the results show that all samples are crystallized in monoclinic structure with P21/n space group without any impurity phase. The temperature dependence of magnetization measurement shows that samples exhibit paramagnetic to ferromagnetic phase transition by decreasing temperature. The values of the $T_{\mathrm {C}}$ are determined as 286, 280 and 278 K for $x =$ 0.4, 0.5 and 0.6 in Pr(Sr1−xPbx)Mn2O6 samples, respectively. Isothermal applied magnetic field-dependent magnetization curves are used to determine both order of magnetic phase transition and magnetic entropy change (ΔSM) value. $-$ ΔSM values are found as 3.68, 3.15 and 2.85 J kg− 1 K− 1 for PSPM-4, PSPM-5 and PSPM-6 samples, respectively. Additionally, magnetic phase transition of the samples is identified as second-order magnetic phase transition that indicates accompanying small thermal and magnetic hysteresis to the samples during the phase transition. Relative cooling power (RCP) values are determined as 282, 233 and 268 J kg− 1 for PSPM-4, PSPM-5 and PSPM-6 samples, respectively.

Tuning of a Vertical Spin Valve with a Monolayer of Single Molecule Magnets

AbstractThe synthesis and the chemisorption from solution of a terbium bis‐phthalocyaninato complex suitable for the functionalization of lanthanum strontium manganite (LSMO) are reported. Two phosphonate groups are introduced in the double decker structure in order to allow the grafting to the ferromagnetic substrate actively used as injection electrode in organic spin valve devices. The covalent bonding of functionalized terbium bis‐phthalocyaninato system on LSMO surface preserves its molecular properties at the nanoscale. X‐ray photoelectron spectroscopy confirms the integrity of the molecules on the LSMO surface and a small magnetic hysteresis reminiscent of the typical single molecule magnet behavior of this system is detected on surface by X‐ray magnetic circular dichroism experiments. The effect of the hybrid magnetic electrode on spin polarized injection is investigated in vertical organic spin valve devices and compared to the behavior of similar spin valves embedding a single diamagnetic layer of alkyl phosphonate molecules analogously chemisorbed on LSMO. Magnetoresistance experiments have evidenced significant alterations of the magneto‐transport by the terbium bis‐phthalocyaninato complex characterized by two distinct temperature regimes, below and above 50 K, respectively.

Magnetocaloric Effect with Very Small Magnetic Hysteresis Losses of CoMn1−x Ti x Ge Alloys

The effects of Ti substitution for Mn and heat treatment on structural, magnetic, and magnetocaloric properties of CoMnGe alloy have been investigated using electron microscopy, X-ray diffraction, calorimetric, and magnetic measurements. According to X-ray diffraction measurements, CoMn1−x Ti x Ge alloys are in a single phase hexagonal structure at room temperature. It is found that the as-cast CoMn0.95Ti0.05Ge alloy shows a magnetostructural phase transition close to room temperature. The transition shows a large magnetic entropy change and a small hysteresis in the isothermal magnetic field-dependent magnetization measurements. After annealing, the phase transition temperature decreases slightly and the magnetization is sharply decreasing at Curie temperature. The sharp change of magnetization at phase transition temperature is accompanied by a significant increase in the magnetic entropy change, i.e., magnetic entropy change value for the magnetic field change of 1 T was increased from −3.3 to −6.3 J kg−1 K−1. Moreover, after annealing, hysteresis losses reduced significantly for ∆H = 7 T. Accordingly, the heat treatment has a significant effect on magnetocaloric properties of the CoMn0.95Ti0.05Ge alloy.

Rare-earth high-entropy alloys with giant magnetocaloric effect

In this paper, we report the development of rare-earth high-entropy alloys (RE-HEA) with multiple principle elements randomly distributed on a single hexagonal close-packed (HCP) lattice. Our work demonstrated that it is the entropy, rather than other atomic factors such as enthalpy, atomic size and electronegativity, that dictates phase formation in the current rare-earth alloy system. The high configuration entropy stabilized the crystalline structure from phase transformation during cooling, whereas a second-order magnetic phase transition occurred at its Neel temperature. The quinary RE-HEA exhibited a small magnetic hysteresis and the largest refrigerant capacity (about 627 J kg−1 at the 5 T magnetic field) reported to date, along with respectable mechanical properties. Our analysis indicates that the strong chemical disorder resulted from the high configuration entropy makes magnetic ordering in the HEA difficult, thus giving rise to a sluggish magnetic phase transition and enhanced magnetocaloric effect. Our findings evidenced that RE-HEAs have great potential to be used as magnetic refrigerants and the alloy-design concept of HEAs can be employed to develop novel high-performance magnetocaloric materials.