This work presents the development of template-based, biodegradable microactuators composed of poly-L-lactic acid and magnetic nanorods. They exhibit a magnetoelectric effect, converting external magnetic fields into localized electrical stimuli. The template-based fabrication enables the creation of uniform polymer microactuators with complex morphologies, directional actuation, enhanced energy transfer efficiency, and integrated multifunctionality.

The direct measurements of the adiabatic temperature change under cyclic conditions have been carried out for Fe48Rh52 alloys obtained by different heat treatment protocols. Furthermore, the magnetocaloric long-term performance has been estimated. The results demonstrate that the degradation of the magnetocaloric properties observed in FeRh can depend on the microstructure of the alloys. Besides, the selection of the cycling temperature can affect the performance as well. The magnetic measurements carried out after the cyclic experiment revealed a shift of the transition towards lower temperatures, which can be correlated to the possible stress that was accumulated during the repetitive magnetostructural transition. Then, it has been shown that the degraded material can be healed by a low temperature annealing those results in the recovery of the magnetostructural transition. The outcome can give a hint for the efficient design of magnetocaloric alloys and the selection of the working temperature in order to diminish the degradation effects.

A model of a “smart” composite based on a thermosensitive PNIPAM polymer deposited on a FeRh substrate with a modified periodic microstructure was proposed. The initial parameters of the model were determined from the properties of the actual composite sample and its components. Cooling of the sample using a magnetic field was shown by two independent methods, and at ~37 °C, it was −5.5 °C when a magnetic field of 1.8 T was applied. Based on experimental data, models of traditional and modified PNIPAM/FeRh composites were constructed. Calculations show that surface modification allows for an increase in the activation time for a polymer layer that is 20 µm thick from ~20 ms for a conventional composite to ~60 ms for a modified composite. Modification of the surface in the form of wells can be used to more effectively implement the idea of loading and releasing drugs for potential biomedical applications.

The smart thermoresponsive composite of PNIPAM/FeRh by chemical grafting of PNIPAM polymer on substrate of FeRh alloy were fabricated and studied. The characteristic peaks at 1690 (C=O), 2480–3000 (CH), and 3280 (N–H) observed on IR-FTIR spectra of PNIPAM/FeRh corresponded to the functional groups of PNIPAM and confirmed grafting of the polymer on the surface of FeRh substrate. The measurements of wetting demonstrated the changes of contact wetting angle from 69.3±1.5° at 27 °C to 76.9±1.2° at 40 °C attributed with transformation of PNIPAM polymer from the hydrated to the dehydrated state due phase transition with lower critical temperature at ~32 °C. The changes in surface topography of PNIPAM polymer in results of phase transition with lower critical solution temperature in PNIPAM were observed using atomic force microscopy measurements in temperature range 30–50 °C in heating and cooling.

FeRh-based alloys are unique objects, the study of which allows us to identify new features of first-order magnetic phase transitions. Doping of an alloy often leads to significant changes in its magnetic properties. This paper examines the structural, magnetic, transport and caloric properties of iron-rhodium alloys with different cobalt doping with varying cobalt content (0-1.8 at%). Doping the alloy with less than 2 at% cobalt resulted in a decrease in the phase transition temperature by 200 K. Based on the results obtained, a relationship was established between the magnetic properties and the heterogeneity of the elemental composition of the samples. It was also demonstrated that significant changes in the parameters of the magnetic phase transition of the alloy upon alloying are largely determined by the electronic properties. Considering the sensitivity of the alloy properties to the cobalt content, we develop a novel methodology for quantifying local compositional variations using temperature-dependent measurements, demonstrating its superior sensitivity compared to conventional techniques. The strong correlation between magnetocaloric response and cobalt concentration highlights the importance of precise composition control for applications.

Mono and multicaloric effects in Fe48Rh52 alloy under applied magnetic field, uniaxial tension and their combination were studied by direct method. It was found that for single cases, the inverse caloric effect was observed with delta TAD = -2.9 K (1T) at 330 K in the case of the magnetocaloric effect and delta TAD = -0.5 K (104 MPa) at 328 K in the case of the elastocaloric effect. The combination co-application of the external 1 T magnetic field and a 104 MPa tensile results to the observation of a synergistic effect with delta TAD = -3.4 K at 330 K when a, which exceeds similar values for mono caloric effects. As was shown from comparison of calculation and experiments multicaloric effect it is not a sum of mono caloric effects and several factors as geometry of the sample as well the protocol for applying external fields should be taken into account. It was shown that the distribution of mechanical stresses in the Fe48Rh52 sample with a geometry in the shape of a plate with holes is heterogeneous, which should be taken into account when measuring calorific effects using tension through holes

Materials with a first-order magnetic phase transition demonstrate colossal changes in physical properties near the phase transition temperature. However, the mechanisms of phase transition occurrence are not fully understood. In this work, using the Fe48Rh52 alloy as an example, we study the near-surface magnetic and structural properties of the alloy near the phase transition temperature. Analysis of images obtained using the magnetooptic Kerr effect at different temperatures allowed us to separate the contributions from nucleation and growth of the ferromagnetic phase during the phase transition. Approximation of experimental data by the proposed model allowed us to estimate the surface energy of ferromagnetic clusters with different micromagnetic structures. The work also shows the influence of microscopic features on the formation of macroscopic properties of the alloy.

The ability to control by physical properties of the thermoresponsive polymer of PNIPAM by magnetocaloric effect was demonstrated by in-situ experiments on PNIPAM/FeRh smart composite. The concept of drug release loaded in smart composite by applying of 3 T magnetic field was demonstrated using an example of doxorubicin. Released results of the magnetic field applying the drug were detected using IV-VIS and Raman spectroscopy. In vitro, studies have demonstrated a high degree of PNIPAM/FeRh scaffold biocompatibility for primary mouse embryonic fibroblasts (PMEF) cell culture. PMEFs effectively ad-hered to the PNIPAM/FeRh scaffold surface and showed high metabolic and proliferative activity for 72 h after seeding.

The magnetic and magnetocaloric properties of gaudefroyite minerals were studied. The magnetocaloric effect was investigated by direct and indirect methods in the temperature range 4.2-40 K and magnetic field up to 10 T. The magnetization was measured in a low magnetic field (200 Oe) with zero-field cooled and field cooling protocol and previous observation of typical spin glass behavior was confirmed. The giant magnetic entropy changes with anisotropic behavior and maximums |Delta Delta Sm|= m |= 17 J kg- 1 K-1 (H||c) at 18 K and |Delta Sm|= Delta S m |= 20 J kg- 1 K-1 (H||ab) at 12 K at an applied magnetic field 10 T were observed. The direct measurements of the magnetocaloric effect demonstrated the maximum of adiabatic temperature changes of Delta T ad = 11 K at a magnetic field change of 10 T (H||ab) at 11.5 K. Obtained values of magnetocaloric parameters for the mineral of gaudefroyite are comparable to promising materials for magnetic crycooling technologies (for example, hydrogen (LH2) 2 ) liquefaction) and have an advantage for the absence of rare-earth elements in the gaudefroyite.

The magnetic and magnetocaloric properties of a MnAs single crystal have been studied along different crystallographic directions in the temperature range of the first-order magnetic phase transition. The constants of magnetocrystalline anisotropy, K-1 and K-2, were determined below the transition temperature by the Sucksmith-Thompson method. It was found that the energy of magnetocrystalline anisotropy decreases with increasing temperature. The results highlighted the impact of shape anisotropy and the magnetic prehistory of the sample on the maximum value of -Delta S-m. The anisotropy of the -Delta S-m value was observed for different crystallographic directions; the -Delta S-m value reaches its maximum of 35 J center dot kg(-1)center dot K-1 in the [001] direction, while 29 J center dot kg(-1)center dot K-1 in the [110] direction. The probability of overestimating the Delta S-m(T) values when using Maxwell's equation instead of the Clausius-Clapeyron formula is shown.

The possibility observation of the electric field controlled multicaloric response through quasi-isostatic compression as a result of the converse piezoelectric effect was demonstrated on the cylindrical type magnetoelectric composite MnAs/PZT. It was shown that an electric voltage of 100 V corresponding to an electric field of E similar to 0.3 kV/mm applied to the walls of the piezoelectric component PZT of the MnAs/PZT composite contributes to an increase in the maximum adiabatic temperature change by 0.2 K in the temperature range of the magnetostructural phase transition of MnAs similar to 317 K at a magnetic field change of 1.8 T. Numerical analysis using the finite element method has shown that an electric field voltage of 100 V is capable of creating a quasi-isostatic mechanical stress in the region inside a cylindrical PZT tube of similar to 3 MPa. Moreover, in the region of weak pressures up to 10 MPa, the contribution to the total adiabatic temperature change from piezo-mechanical compression linearly depends on the electrical voltage that can be used for control by magnetic and caloric properties of multicaloric materials. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Accurate measuring the temperature of materials, especially in high pulsed and alternating magnetic fields, represents a major challenge in magnetic and, in particular, magnetocaloric research. The disadvantages of the used contact temperature sensors (microthermocouples and film thermistors) are: (1) the effect of electromagnetic interference on their indications, which is proportional to the time derivative of the magnetic field, (2) their relatively long response time due to thermal inertia, and (3) the impossibility of accurate measurement temperatures of thin and microstructured samples. The described difficulties can be avoided by using non-contact optical methods for measuring the temperature of magnets in high magnetic fields. In this review, we describe non-contact optical methods for measuring the magnetocaloric effect using known materials as an example, and provide a comparative analysis of the main characteristics of these methods, such as: maximal magnetic field, sampling frequency, time constant and spectral range of the detector, and temperature error and resolution.

Using commercially available components, a compact laboratory-type prototype has been developed and assembled to demonstrate single and multicaloric effects arising from single and cyclic applications of magnetic fields and uniaxial mechanical loads. Using the example of the LaFe11.4Mn0.3Si1.3H1.6 alloy with a first-order phase transition near room temperature, the possibility of observing magnetocaloric, elastocaloric, and multicaloric effects is demonstrated. It is shown that by selecting protocols for applying combined external influences: magnetic field and mechanical load, it is possible to observe a synergistic effect for adiabatic temperature change, which amounts to 1.17 K (0.31 T and 19 MPa) at a temperature of 291.5 K for the multicaloric effect, which exceeds the corresponding value of |ΔT| = 0.75 K (0.31 T) at a temperature of 291.65 K for the magnetocaloric effect. The proposed approaches and obtained results can be used for the development of new prototypes of multicaloric cooling systems and the optimization of current ones.

β-tricalcium phosphate (β-TCP) is a promising material in regenerative traumatology for the creation of bone implants. Previously, it was established that doping the structure with certain cations can reduce the growth of bacterial activity. Recently, much attention has been paid to co-doped β-TCP, that is explained by their ability, on the one hand, to reduce cytotoxicity for cells of the human organism, on the other hand, to achieve a successful antibacterial effect. Sr, Cu-co-doped solid solutions of the composition Ca9.5–xSrxCu(PO4)7 was obtained by the method of solid-phase reactions. The Rietveld method of structural refinement revealed the presence of Sr2+ ions in four crystal sites: M1, M2, M3, and M4. The M5 site is completely occupied by Cu2+. Isomorphic substitution of Ca2+ → (Sr2+and Cu2+) expands the concentration limits of the existence of the solid solution with the β-TCP structure. No additional phases were formed up to x = 4.5 in Ca9.5–xSrxCu(PO4)7. Biocompatibility tests were performed on cell lines of human bone marrow mesenchymal stromal cells (hMSC), human fibroblasts (MRC-5) and osteoblasts (U-2OS). It was demonstrated that cytotoxicity exhibited a concentration dependence, along with an increase in osteogenesis and cell proliferation. Ca9.5–xSrxCu(PO4)7 powders showed significant inhibitory activity against pathogenic strains Escherichia coli and Staphylococcus aureus. Piezoelectric properties of Ca9.5–xSrxCu(PO4)7 were investigated. Possible ways to achieve high piezoelectric response are discussed. The combination of bioactive properties of Ca9.5–xSrxCu(PO4)7 renders them multifunctional materials suitable for bone substitutes.

Samples of composites with different porosity and surface roughness based on LaFe11.4Mn0.3Si1.3H1.6 (LFMSH) alloy powders were obtained, their magnetocaloric properties were studied by the direct method in cyclic magnetic fields of μ0H = 1.2 T with a frequency of 2 Hz. The maximal value of the adiabatic temperature change in pure LFMSH powder was ΔT = 3 K at T0 = 287 K in the sample cooling regime, and for composite samples, this value was approximately two times lower than that in the powder. The effect of Mn and H atoms on the electronic structure and local magnetic characteristics of the initial La(Fe,Si)13 alloy was studied using electron density functional theory. Replacement of some Fe atoms with Mn reduces the total magnetic moment and somewhat lowers the Curie temperature. In contrast, hydrogenation leads to an increase in exchange interactions between Fe atoms located at the vertices of the icosahedron and an increase in the Curie temperature.

The possibility of electric field control of magnetocaloric effect through quasi-isostatic compression as a result of the converse piezoelectric effect was demonstrated on cylindrical type magnetoelectric composite MnAs/PZT. It was shown that an electric voltage of 100 V corresponding to an electric field of E  0.3 kV/mm applied to the walls of the piezoelectric component PZT of the MnAs/PZT composite contributes to an increase in the maximum adiabatic temperature change by 0.2 K in the temperature range of the magnetostructural phase transition of MnAs  317 K at magnetic field change of 1.8 T. Calculations using the finite element method have shown that an electric field voltage of 100 V is capable of creating a quasi-isostatic mechanical stress in the region inside a cylindrical PZT tube of  3 MPa. Moreover, in the region of weak pressures up to 10 MPa, the contribution to the MCE from piezo compression linearly depends on the electrical voltage that can be used for control the MCE

The new xMnAs/(1 − x)PMN–PT (x = 0.2, 0.3) multicaloric composites, consisting of the modified PMN–PT-based relaxor-type ferroelectric ceramics and ferromagnetic compound of MnAs were fabricated, and their structure, magnetic, dielectric properties, and caloric effects were studied. Both components of the multicaloric composite have phase transition temperatures around 315 K, and large electrocaloric (~0.27 K at 20 kV/cm) and magnetocaloric (~13 K at 5 T) effects around this temperature were observed. As expected, composite samples exhibit a decrease in magnetocaloric effect (<1.4 K at 4 T) in comparison with an initial MnAs magnetic component (6.7 K at 4 T), but some interesting phenomena associated with magnetoelectric interaction between ferromagnetic and ferroelectric components were observed. Thus, a composite with x = 0.2 exhibits a double maximum in isothermal magnetic entropy changes, while a composite with x = 0.3 demonstrates behavior more similar to MnAs. Based on the results of experiments, the model of the multicaloric effect in an MnAs/PMN–PT composite was developed and different scenario observations of multicaloric response were modeled. In the framework of the proposed model, it was shown that boosting of caloric effect could be achieved by (1) compilation of ferromagnetic and ferroelectric components with large caloric effects in selected mass ratio and phase transition temperature; and (2) choosing of magnetic and electric field coapplying protocol. The 0.3MnAs/0.7PMN–PT composite was concluded to be the optimal multicaloric composite and a phase shift ∆φ = −π/4 between applied manetic fields can provide a synergetic caloric effect at a working point of 316 K.

Nowadays, magnetoelectric nanomaterials are on their way to finding wide applications in biomedicine for various cancer and neurological disease treatment, which is mainly restricted by their relatively high toxicity and complex synthesis. This study for the first time reports novel magnetoelectric nanocomposites of CoxFe3−xO4-BaTiO3 series with tuned magnetic phase structures, which were synthesized via a two-step chemical approach in polyol media. The magnetic CoxFe3−xO4 phases with x = 0.0, 0.5, and 1.0 were obtained by thermal decomposition in triethylene glycol media. The magnetoelectric nanocomposites were synthesized by the decomposition of barium titanate precursors in the presence of a magnetic phase under solvothermal conditions and subsequent annealing at 700 °C. X-ray diffraction revealed the presence of both spinel and perovskite phases after annealing with average crystallite sizes in the range of 9.0–14.5 nm. Transmission electron microscopy data showed two-phase composite nanostructures consisting of ferrites and barium titanate. The presence of interfacial connections between magnetic and ferroelectric phases was confirmed by high-resolution transmission electron microscopy. Magnetization data showed expected ferrimagnetic behavior and σs decrease after the nanocomposite formation. Magnetoelectric coefficient measurements after the annealing showed non-linear change with a maximum of 89 mV/cm*Oe with x = 0.5, 74 mV/cm*Oe with x = 0, and a minimum of 50 mV/cm*Oe with x = 0.0 core composition, that corresponds with the coercive force of the nanocomposites: 240 Oe, 89 Oe and 36 Oe, respectively. The obtained nanocomposites show low toxicity in the whole studied concentration range of 25–400 μg/mL on CT-26 cancer cells. The synthesized nanocomposites show low cytotoxicity and high magnetoelectric effects, therefore they can find wide applications in biomedicine.

The performance parameters for characterizing the electrocaloric effect are isothermal entropy change and the adiabatic temperature change,respectively.This paper reviews the electrocaloric effect of ferroelectric materials based on different theoretical models.First,it provides four different calculation scales(the first-principle-based effective Hamiltonian,the Landau-Devonshire thermody-namic theory,phase-field simulation,and finite element analysis)to explain the basic theory of calculating the electrocaloric effect.Then,it comprehensively reviews the recent progress of these methods in regulating the electrocaloric effect and the generation mechanism of the electrocaloric effect.Finally,it summarizes and anticipates the exploration of more novel electrocaloric materials based on the framework constructed by the different computational methods.

The effect of a high magnetic field up to 12 T and a high hydrostatic pressure up to 12 kbar on the stability of the metamagnetic isostructural phase transition and the multicaloric effect of Fe49Rh51 alloy has been studied. The phase transition temperature shifts under the magnetic field and the hydrostatic pressure on with the rates of dTm/μ0dH = −9.2 K/T and dTm/dP = 3.4 K/kbar, respectively. The magnetocaloric and multicaloric (under two external fields) effects were studied via indirect method using Maxwell relations. The maximum of the entropy change is increasing toward the high temperature region from ∆S~2.5 J/(kg K) at 305 K to ∆S~2.7 J/(kg K) at 344 K under simultaneously applied magnetic field of 0.97 T and hydrostatic pressure of 12 kbar. The obtained results were explained using the first-principle calculations of Gibbs energies and the phonon spectra of the ferromagnetic and the antiferromagnetic phases. Taking into account the low concentration of antisite defects in the calculation cells allows us to reproduce the experimental dTm/dP coefficient.