Isothermal Magnetization Curves Research Articles

Critical behavior of quasi-two-dimensional ferromagnet Cr1.04Te2

Abstract The self-intercalation of Cr into pristine two-dimensional (2D) van der Waals ferromagnetic CrTe2, which forms chromium tellurides (Cr x Te2), has garnered interest due to their remarkable magnetic characteristics and the wide variety of chemical compositions available. Here, comprehensive basic characterization and magnetic studies are conducted on quasi-2D ferromagnetic Cr1.04Te2 crystals. Measurements of the isothermal magnetization curves are conducted around the critical temperature to systematically investigate the critical behavior. Specifically, the critical exponents β = 0.2399, γ = 0.859, and δ = 4.3498, as well as the Curie temperature T C = 249.56 K, are determined using various methods, including the modified Arrott plots, the Kouvel–Fisher method, the Widom scaling method, and the critical isotherm analysis. These results indicate that the tricritical mean-field model accurately represents the critical behavior of Cr1.04Te2. A magnetic phase diagram with tricritical phenomenon is thus constructed. Further investigations confirm that the critical exponents obtained conform to the scalar equation near T C, indicating their self-consistency and reliability. Our work sheds light on the magnetic properties of quasi-2D Cr1.04Te2, broadening the scope of the van der Waals crystals for developments of future spintronic devices operable at room temperature.

Role of Griffiths phase on magnetocaloric properties and critical behavior of half-doped manganites [La0.5Sr0.5-xCaxMnO3(x = 0, 0.25, 0.5)

In this article, a comprehensive study of the effect of calcium substitution on structural magnetic, magnetocaloric properties, and role of Griffiths phase on magnetocaloric properties of half-doped manganites La0.5Sr0.5-xCaxMnO3(x=0,0.25,0.5)] have been presented. A structural phase transition I4/mcm - Pbnm is observed in the whole series. The system exhibits two magnetic transitions for Ca-00 and Ca-25, whereas only one phase transition is observed for Ca-50. Paramagnetic (PM)-ferromagnetic (FM) transition is observed in the whole series and ferromagnetic (FM) - antiferromagnetic (AFM) phase transition is only observed in Ca-25. Interestingly, short range FM clusters exist in the PM matrix of Ca-50, which is a signature of Griffiths phase (GP). The confirmation of GP has been carried out by performing iso-field magnetization measurements at 200 Oe, 500 Oe, and 1 kOe, respectively. Further magnetocaloric properties have been discussed on the basis of isothermal magnetization curves recorded at certain temperature intervals. Calcium substitution favors the enhancement of magnetic entropy change in the series, especially for Ca-50, a magnetic entropy change of 4.5J/(kgK) with relative cooling power of 180J/kg under 5T magnetic field was observed. Iso-field magnetization and magnetocaloric effect along with critical behavior analysis have been carried out to probe the GP and other inhomogeneities present in the respective series.

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.

Paleomagnetism of the Rio Perdido mafic dike swarm (1110 Ma) and the paleogeography of Amazonia and its role for supercontinents Rodinia and Gondwana

The Rio Apa Terrane (RAT) is situated at the south end of the Amazonian Craton (AC) separated from it by the aulacogen Tucavaca belt. It encompasses basement rocks that evolved mainly during the Paleoproterozoic. Its relationship to the AC during Proterozoic is yet undefined, although geologic, geochronologic and isotopic evidence suggest it was close to the Ventuari-Tapajós and Rio Negro-Juruena Provinces at Paleoproterozoic and linked to southwestern AC at ca. 1320 Ma. Aiming to elucidate the paleogeographic relation of the RAT to the AC during the Proterozoic, we performed a paleomagnetic study of the 1110 Ma Rio Perdido mafic dike swarm that crosscut the RAT. These dikes strike preferentially WNW-ESE and are mostly undeformed and unmetamorphosed. Magnetic experiments (hysteresis curves, isothermal remanent magnetization (IRM) curves, thermomagnetic curves and first order reverse curves-FORCs) revealed pseudo-single domain (PSD) Ti-poor titanomagnetite as the main magnetic carrier in these dikes. Alternating field (AF) and thermal demagnetization were efficient in isolating southwestern and northeastern directions with low inclinations, whose mean direction (Dec = 51.8°, Inc = −0.8°, N = 14, α95 = 13.8°, k = 9.3) yielded the paleomagnetic pole (RP) at 34.8°S/197.3° (A95 = 10.9°). This pole passed a baked contact test and meets 6 out of 7 pole reliability criteria (R = 6). The Rio Perdido pole implies that RAT could be linked to the southwestern AC at 1110 Ma but rotated counterclockwise ∼ 110° related to its present position. The AC linked to RAT probably belonged to the 1100 Ma Umkondia megacontinent which later collided with Laurentia during the formation of Rodinia at ca. 1000–900 Ma. Also, paleomagnetic data suggest that the RAT and the southwestern AC (Paraguá Terrane) were linked to Ventuari-Tapajós and Rio Negro-Juruena provinces at ca. 1780 Ma and had a joint geological evolution during the Paleo- and Mesoproterozoic. Finally, during the amalgamation of West Gondwana, the RAT rotated clockwise to its present position.

Superconductivity-Electron Count Relationship in Heusler Phases-the Case of LiPd2Si.

We report superconductivity in the full Heusler compound LiPd2Si (space group Fm3̅m, No. 225) at a critical temperature of Tc = 1.3 K and a normalized heat capacity jump at Tc, ΔC/γTc = 1.1. The low-temperature isothermal magnetization curves imply type-I superconductivity, as previously observed in LiPd2Ge. We show, based on density functional theory calculations and using the molecular orbital theory approach, that while LiPd2Si and LiPd2Ge share the Pd cubic cage motif that is found in most of the reported Heusler superconductors, they show distinctive features in the electronic structure. This is due to the fact that Li occupies the site which, in other compounds, is filled with an early transition metal or a rare-earth metal. Thus, while a simple valence electron count-property relationship is useful in predicting and tuning Heusler materials, inclusion of the symmetry of interacting frontier orbitals is also necessary for the best understanding.

Study of the d-f magnetic interaction in V-doped RCrO4 (R[dbnd]Tb, Dy, Er and Yb) compounds

In this work, we have carried out a detailed study of the structural and magnetic properties of RVxCr1−xO4 (RTb, Dy, Er, and Yb; x = 0.0, 0.3, 0.5, 0.7 and 1.0) compounds obtained by the co-precipitation method. X-ray diffraction data using Rietveld refinement shows that all samples present a single phase consistent with the zircon-type structure (I41/amd space group (No. 141)). The lattice parameter changes as a function of both V-concentration and the rare earth ion. The analyses on T-dependent magnetic susceptibility indicate that RCrO4 samples are ferromagnetic while RVxCr1−xO4 ones are antiferromagnetic for x = 0.7 and 1.0. The increase of magnetic transition temperatures from 3 K (RVO4) to 20 K (RCrO4) can be an indicator that the R–Cr magnetic interaction takes an important role in the magnetic properties in these compounds. Isothermal magnetization curves measured at T = 2 K for all samples reinforce the ferromagnetic character of RCrO4 samples once they present remanence, coercivity, and magnetization saturation. However, the fact that the expected gJJ value for the full multiplet is not reached for all samples must be associated with the crystal electric field on the rare earth ion.

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.

Table-like magnetocaloric effect due to field-induced inter-cluster interactions in Eu0.5Sr0.5MnO3–EuMnO3 composites

The table-like behavior of the magnetic entropy change is generally observed in rare-earth-based alloys (e.g. La(Fe,Si)13, Gd50Co45Fe5, Gd56Ni15Al27Zr2, GdCo x Al y etc). Here, we report similar table-like behavior in a bulk perovskite Eu0.5Sr0.5MnO3–EuMnO3 composite system with a working temperature span of ∼80 K for a field change of ∼70 kOe. AC susceptibility and time-dependent DC magnetization relaxation measurements confirm the presence of interacting ferromagnetic clusters with a Vogel–Fulcher freezing temperature of 42.7 K. The Langevin function fittings of the isothermal magnetization curves show a non-monotonous variation of cluster size with temperature. We propose a model for the high-field dependency of the ferromagnetic cluster coupling in the composite system. This widens the transition temperature region of long-range order formation and hence gives rise to the table-like magnetocaloric effect in Eu0.5Sr0.5MnO3–EuMnO3 composite systems.

Tracing titanomagnetite alteration with magnetic measurements at cryogenic temperatures

SUMMARY Titanomagnetite containing up to 0.6–0.7 Ti atoms per formula unit is a primary magnetic mineral phase in submarine basalts and in some terrestrial volcanic rocks. On a geological timescale, it often undergoes alteration, forming new magnetic phases that may acquire (thermo)chemical remanent magnetization. The initial stage of this natural process can be modelled by prolonged laboratory annealing at moderately elevated temperatures. In this study, our goal is to characterize the alteration products resulting from annealing a submarine basalt containing homogeneous titanomagnetite Fe3−xTixO4 (x ≈ 0.46) at temperatures of 355, 500 and 550 °C for up to 375 hr, by examining their magnetic properties over a wide range of temperatures. The effect of extended annealing is most apparent in the low-temperature magnetic properties. In the fresh sample, a magnetic transition is observed at 58 K. Below the transition temperature, the field-cooled (FC) and zero-field-cooled (ZFC) saturation isothermal remanent magnetization (SIRM) curves are separated by a tell-tale triangular-shaped area, characteristic for titanomagnetites of intermediate composition. The room-temperature SIRM (RT-SIRM) cycle to 1.8 K in zero field has a characteristic concave-up shape and is nearly reversible. For the annealed samples, the magnetic transition temperature shifts to lower temperatures, and the shape of the curves above the transition changes from concave-up to concave-down. The shape of the RT-SIRM cycles also progressively changes with increasing annealing time. The SIRM loss after the cycle increases up to ∼30 per cent for the samples annealed for 375 hr at 355 °C, and for 110 hr at 500 and 550 °C. The Curie temperatures of the newly formed magnetic phases exceed the Curie temperature of the fresh sample (205 °C) by up to 350 °C. While this effect is most commonly attributed to extensive single-phase oxidation (maghemitization), the behaviour observed at cryogenic temperatures appears incompatible with the known properties of highly oxidized titanomaghemites. Therefore, we propose that, at least in the initial stage of the ‘dry’, that is, not involving hydrothermalism, alteration of titanomagnetite, temperature- and time-controlled cation reordering is the primary mechanism driving changes in both low- and high-temperature magnetic properties.

Effect of an aluminum layer deposited with magnetron sputtering on magnetic and remanence properties of Sr-hexaferrite

This work deals with the effect that aluminum deposited on the strontium hexaferrite has on the magnetic and remanence properties. The aluminum was deposited using magnetron sputtering and the deposit thickness was varied through two deposition times. The presence of the aluminum was corroborated by X-ray diffraction and scanning electron microscopy. The magnetic characterization showed an increment in remanence squareness (Mr/Ms), while the maximum energy product (BHmax) exhibited a large increment regarding the hexaferrite without aluminum. Isothermal remanent magnetization (IRM) and direct current demagnetization (DCD) curves were measured for two samples with different amounts of deposited aluminum and for the strontium hexaferrite without aluminum. The Henkel plots and δM curves were discussed in the Stoner-Wohlfarth framework. Results show a diminishing of demagnetizing-like interactions as the deposited aluminum increases on the hexaferrite surface. This behavior suggests that aluminum promotes the emergence of a type of exchange interaction with a magnetizing effect.

Multiple spin switching and magnetocaloric effects in orthoferrite Yb0.25Tb0.75FeO3 single crystal

YbFeO3 exhibits spin switching (SSW) and spin reorientation transition (SRT) at low temperatures, but its mediocre magnetocaloric properties limit its further applications. As for TbFeO3 showing a large magnetocaloric effect, its SSW is missing. Motivated by this, we chemically put Yb and Tb with a ratio of 1:3 on the rare-earth site. Potential applications of magnetic and magnetocaloric properties are both preserved in one single phase Yb0.25Tb0.75FeO3, which is exceptional among the rare-earth orthoferrites. Spin switching temperature (TSSW) in the field-cooled-cooling mode increases to around 100 K compared with YbFeO3. A novel multiple SSW emerges in the field-cooled-warming mode originating from the complex competing magnetic interactions between Yb/Tb and Fe sublattices. We also addressed the mechanism of spin modification of magnetic ions with temperatures. Arrott plots created from the isothermal magnetization curves demonstrate that SRT is a second-order phase transition. The negative entropy change (refrigeration capacity) vs. temperatures [−∆Sm(RC) vs. T] diagrams indicate that the −∆Sm(RC) are effectively increased compared with YbFeO3 by rare-earth doping. The pronounced magnetic refrigeration performance and SSW effect with a low-field dependence make it promising to be employed in both magnetic sensing and refrigeration devices.

On the magnetocaloric effect and the spin-phonon coupling in the multiferroic GdMn2O5

The spin-phonon coupling and the magnetocaloric effect (MCE) in polycrystalline GdMn2O5 are investigated by Raman spectroscopy and isothermal magnetization curves. The frequencies of 680 and 700 cm−1 modes show anomalous temperature variations suggesting a strong spin-phonon coupling below the Néel temperature TN ∼ 38 K. The frequency deviation from standard temperature dependence is quantitatively interpreted within a simplified theoretical model accounting for the modulation of the exchange interaction by phonon vibrations. A relatively large magnetic entropy change, ∆Smax = 9.8 J/(kg K), is also achieved with magnetic fields up to 70 kOe. We found that the refrigerant capacity values in GdMn2O5, at different magnetic fields, are quite similar to those of TbMn2O5 and HoMn2O5 in the polycrystalline average approximation. However, the low-cost fabrication of the polycrystalline samples of GdMn2O5 and their large electric polarisation makes this material more suitable for possible cooperative magneto-electrocaloric refrigeration.

Substantial enhancement in magnetic and magnetodielectric properties of 0.7(Bi2Fe4O9)-0.3(La0.67Sr0.33MnO3) composite

In pursuit of room-temperature magnetoelectric materials for numerous technological applications various materials are vigorously explored. Such is the motivation behind the synthesis of 0.7(Bi2Fe4O9)-0.3(La0.67Sr0.33MnO3) composite. The phase purity and structural analysis are examined through Rietveld refinement of room temperature X-ray diffraction (XRD) pattern, which shows that the composite has ‘Pbam + Pbnm’ phases. X-ray photoelectron spectroscopy confirmed the presence of mixed valence state of magnetic ions i.e. Fe2+ (41%), Fe3+ (45%), Fe4+ (14%) and Mn2+ (88%), Mn3+ (12%) favouring superexchange and double exchange interactions contributing to enhanced magnetizations. The presence of weak ferromagnetism in the composite is confirmed by large irreversibility in ZFC-FC data, isothermal magnetization curves and Arrott plots throughout the wide temperature range (10–300 K). High value of coercivity (Hc) is observed with an increase in temperature which indicates magnetic anisotropy in the system. Along with that, a plausible magnetodielectric (MD) coupling is evidenced in temperature dependent dielectric (ε′) and tan loss. Later, it is verified through intrinsic MD results carried out at higher frequency. At room temperature, the MD effect is found to be ∼2%. A contrasting behaviour in magnetic field variation of MD% is at 10 K and 300 K. However, a butterfly-shaped MD curve is evidenced where MD% ∼0.21% at 10 K. Lastly, Landau free energy expression confirmed that MD effect emerges from the coupling term ‘γP2M2′ where γ is ∼1.6 × 10−2 (emu/g)−2 and ∼1.1 × 10−2 (emu/g)−2 at 10 K and 300 K respectively. Thus, the above findings highlight the significance of the composite as a potential room temperature magnetoelectric material for device applications.

Structural, magnetic and magnetocaloric properties of Laves phase (Gd,Sm)Co[formula omitted] compound

In the present work, the structural, magnetic, and magnetocaloric properties of the intermetallic Gd1−xSmxCo2 (x=0.5,0.6 and 0.7) compounds have been systematically studied. Samples were prepared by arc melting under high pure argon and homogenized at 800 K to minimize the impurity phases. X-ray diffraction (XRD) coupled with Rietveld analysis has shown that all samples crystallize in the cubic MgCu2-type structure (Space group Fd-3 m). Refinement results show that the unit cell parameter increases with increasing Sm content. The magnetic measurement reveals that the Sm content reduces the Curie temperature TC from 404 (for x=0) to 263 K (for x=0.7). The magnetic entropy change of the samples as function of temperature and applied magnetic field were calculated from the isothermal magnetization curves using Maxwell relation. The relative cooling power RCP and the temperature-averaged entropy change (TEC) have been reported. Furthermore, the magnetocaloric behavior is studied using the scaling laws and the phenomenological universal curve.

Crystal growth of CeMn0.85Sb2: Absence of magnetic order of Ce-sublattice

Single crystals of CeMn0.85Sb2 have been successfully synthesized by using the Bi as flux. Analysis of single crystal x-ray diffraction data confirms that CeMn0.85Sb2 crystallizes in the HfCuSi2-type structure with the space group P4/nmm (No. 129). In the case of H||c, CeMn0.85Sb2 displays a robust antiferromagnetic transition at ∼160 K for Mn-sublattice, and there is no sign of magnetic order regarding Ce-sublattice. In the case of H ⊥ c, the Mn-sublattice shows signs of magnetic order at 160 K and 116 K, indicating a possible spin reorientation. There is no sign of magnetic order for the Ce-sublattice either, but, alternating current magnetic susceptibility measurements reveal a spin glass state below 18 K in the case of H ⊥ c. Isothermal magnetization curves measured below magnetic order with H ⊥ c show saturation and even large hysteresis at 2 K, indicating the presence of a ferromagnetic component. In addition, a field-induced spin-flop transition is observed in the case of H ⊥ c, indicating a field-induced spin reorientation of Mn spins. Electrical resistivity measurements indicate a metallic nature for CeMn0.85Sb2 and large anisotropy which is consistent with its quasi-two-dimensional layered structure.

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 ${T}_{N3,N2}&lt;T&lt;{T}_{N1}$ 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.

Structural, magnetic, and transport properties of Co2CrAl epitaxial thin film

We report the physical properties of Co2CrAl Heusler alloy epitaxial thin films grown on a single-crystalline MgO(001) substrate using a pulsed laser deposition technique. The x-ray diffraction pattern in the θ-2θ mode showed the film growth in a single phase B2-type ordered cubic structure with the presence of (002) and (004) peaks, and the film oriented along the MgO(001) direction. The ϕ scan along the (220) plane confirms the fourfold symmetry, and the epitaxial growth relation is found to be Co2CrAl(001)[100]||MgO(001)[110]. The thickness of about 12 nm is extracted through the analysis of x-ray reflectivity data. The isothermal magnetization (M–H) curves confirm the ferromagnetic (FM) nature of the thin film having significant hysteresis at 5 and 300 K. From the in-plane M–H curves, the saturation magnetization values are determined to be 2.1 μB/f.u. at 5 K and 1.6 μB/f.u. at 300 K, which suggest the soft FM behavior in the film having the coercive field ≈522 Oe at 5 K. The thermomagnetization measurements at 500 Oe magnetic field show the bifurcation between field-cooled and zero-field-cooled curves below about 100 K. The normalized field-cooled magnetization curve follows the T2 dependency, and the analysis reveals the Curie temperature around 335±11 K. Moreover, the low-temperature resistivity indicates semiconducting behavior with the temperature, and we find a negative temperature coefficient of resistivity (5.2×10−4/K).

Integrated experimental and theoretical studies on structural and magnetic properties of thin films of double perovskite ruthenates: Ba2DyRuO6 & Sr2DyRuO6.

Thin films of double perovskite ruthenates, viz., Ba2DyRuO6 (BDRO) and Sr2DyRuO6 (SDRO), have been successfully grown on a SrTiO3 substrate using the pulsed laser deposition technique. The BDRO samples crystallizes in cubic structure, while SDRO exhibits monoclinic structure as revealed in their X-Ray diffraction examination. Temperature-dependent magnetization measurements suggest the presence of ferromagnetism in BDRO, while paramagnetism is present for the SDRO thin film. Surprisingly, both films show canted antiferromagnetism at ∼T = 5 K as revealed in their isothermal magnetization curves. The inverse susceptibility has been fitted to the Curie-Weiss law for the SDRO sample, where the Curie temperature (TC ∼ -336.6 K) has been obtained, thus suggesting the prevalence of antiferromagnetic interactions. The existence of the canted magnetism at a lower temperature may be attributed to the Dzyaloshinskii-Moriya (D-M) interactions in the monoclinic SDRO sample due to structural distortion. However, the emergence of canted antiferromagnetism at lower temperatures (5 K) in the BDRO sample with cubic symmetry having no D-M interactions may be attributed to the various modifications at the surface of the thin films. Overall, a comparison made between the magnetic properties of both the thin films i.e., BDRO & SDRO, reveals the suppression of bulk magnetic ordering when compared to their bulk counterparts. The possible reason for the absence of any magnetic ordering in these thin films may be due to any modifications in superexchange interactions, any exchange bias, stress-strain, or uncompensated spins present in these types of thin films. UV-visible measurements for both the samples reveal a direct influence of the A-site element (Sr/Ba) on their band gaps, i.e., 3.66 eV and 2.59 eV for BDRO and SDRO samples, respectively, hence suggesting their insulating nature. We have also carried out first principles calculations with DFT using the CASTEP software to gain more insights into the experimental data. These thin films with insulating-antiferromagnetic properties may be crucial for "spintronics devices".

Влияние механической деформации на магнитные свойства и магнитокалорический эффект в пленках Gd

In W/Gd/W/MgO heterostructures, the dependence of mechanical stresses in the Gd film on the crystallographic orientation of the MgO substrate was revealed. Variations in the interplanar spacings in MgO in different orientations create tensile elastic stresses up to 0.22 GPa in the Gd film, which are transferred through the damping layer W. It is found that these stresses affect the isothermal magnetization curves, the corresponding change in the magnetic part of the entropy at the Curie point Tc = 293 K, and the relative cooling capacity (RCP). This allows us to consider mechanical stresses as a factor in controlling the magnetocaloric cycle, which increases the efficiency of the refrigeration machine, when mechanical loading is synchronized with the heating-cooling cycles of the ferromagnet.

Influence of mechanical deformation on magnetic properties and magnetocaloric effect in Gd films

In W/Gd/W/MgO heterostructures, the dependence of mechanical stresses in the Gd film on the crystallographic orientation of the MgO substrate was revealed. Variations in the interplanar spacings in MgO in different orientations create tensile elastic stresses up to 0.22 GPa in the Gd film, which are transferred through the damping layer W. It is found that these stresses affect the isothermal magnetization curves, the corresponding change in the magnetic part of the entropy at the Curie point T_c=293 K, and the relative cooling capacity (RCP). This allows us to consider mechanical stresses as a factor in controlling the magnetocaloric cycle, which increases the efficiency of the refrigeration machine, when mechanical loading is synchronized with the heating-cooling cycles of the ferromagnet. Keywords: magnetocaloric effect, entropy, microdeformations, microstresses.