Narrow Thermal Hysteresis Research Articles

Spectroscopic Detection and Theoretical Description of Spin‐Crossover Effect in Co(II)‐terpyridine System

Spin‐crossover (SCO) effect on octahedral Co(II) centers is much rarer and less known than in the case of Fe(II) complexes, although it is no less promising for the development of fundamental research, sophisticated memories, and sensors. The representative compound [Co(terpy)2]I2·2H2O (terpy = 2,2′:6′,2′′‐terpyridine) was synthesized, and its physicochemical properties were studied both experimentally and theoretically. Magnetic experiments revealed a very gradual SCO between a low‐spin state (SCo(II)‐LS = 1/2) and a high‐spin state (SCo(II)‐HS = 3/2) for the pristine sample and an abrupt SCO with a narrow thermal hysteresis around 130 K for the desolvated sample. Moreover, temperature‐dependent vibrational and electronic spectroscopy were employed to track the evolution of spectroscopic features related to SCO and desolvation processes. Additionally, quantum chemical calculations were utilized to determine the electronic structure, molecular orbitals, and vibrations for different spin states at various temperatures, offering a more comprehensive understanding of the compound's spectroscopic and magnetic behaviors. These extensive investigations provide valuable insights into Co(II)‐based SCO materials and their theoretical underpinnings, paving the way for the application of their thermometric properties.

Activating a high-spin iron(II) complex to thermal spin-crossover with an inert non-isomorphous molecular dopant.

[Fe(bpp)2][ClO4]2 (bpp = 2,6-bis{pyrazol-1-yl}pyridine; monoclinic, C2/c) is high-spin between 5-300 K, and crystallises with a highly distorted molecular geometry that lies along the octahedral-trigonal prismatic distortion pathway. In contrast, [Ni(bpp)2][ClO4]2 (monoclinic, P21) adopts a more regular, near-octahedral coordination geometry. Gas phase DFT minimisations (ω-B97X-D/6-311G**) of [M(bpp)2]2+ complexes show the energy penalty associated with that coordination geometry distortion runs as M2+ = Fe2+ (HS) ≈ Mn2+ (HS) < Zn2+ ≈ Co2+ (HS) ≲ Cu2+ ≪ Ni2+ ≪ Ru2+ (LS; HS = high-spin, LS = low-spin). Slowly crystallised solid solutions [FexNi1-x(bpp)2][ClO4]2 with x = 0.53 (1a) and 0.74 (2a) adopt the P21 lattice, while x = 0.87 (3a) and 0.94 (4a) are mixed-phase materials with the high-spin C2/c phase as the major component. These materials exhibit thermal spin-transitions at T½ = 250 ± 1 K which occurs gradually in 1a, and abruptly and with narrow thermal hysteresis in 2a-4a. The transition proceeds to 100% completeness in 1a and 2a; that is, the 26% Ni doping in 2a is enough to convert high-spin [Fe(bpp)2][ClO4]2 into a cooperative, fully SCO-active material. These results were confirmed crystallographically for 1a and 2a, which revealed similarities and differences between these materials and the previously published [FexNi1-x(bpp)2][BF4]2 series. Rapidly precipitated powders with the same compositions (1b-4b) mostly resemble 1a-4a, except that 2b is a mixed-phase material; 2b-4b also contain a fraction of amorphous solid in addition to the two crystal phases. The largest iron fraction that can be accommodated by the P21 phase in this system is 0.7 ± 0.1.

Prediction of narrow HT-SMA thermal hysteresis behaviour using explainable machine learning

The ability to tailor narrow high-temperature thermal hysteresis behaviour in Ti-Ni-based high-transformation temperature shape memory alloys (HT-SMAs) is crucial for the development of the next-generation actuators intended for use in extreme conditions. Equally, the need and the development of tools to accurately predict shape memory alloys (SMA) transformation temperatures also becomes emergent. As such, the purpose of this study is to curate a small dataset from the experimental peer-reviewed literature and develop a practical data-driven machine learning (ML) based model to predict narrow hysteresis in HT-SMA transformations. This study compiles a small dataset based on experimental data and develops at least twelve candidate models using common machine learning and artificial neural network algorithms. Our results show that the XGBoost-based model exhibits the best performance in predicting the narrow thermal hysteresis behaviour in Ti-Ni-based HT-SMAs (i.e., the highest R2 = 0.893 and the lowest RMSE = 5.4). Further, using preselected case studies, the study demonstrates the utility of the relative feature importance, the accumulated local effects (ALE), and the SHapley Additive exPlanations (SHAP) model-agnostic techniques to interpret predicted outcomes and establish a more transparent relationship between the input materials composition descriptors and the predictions. These analyses demonstrate that the explainable ML approach offers practitioners a more transparent design tool, not only to predict the narrow hysteresis behaviour in HT-SMA transformations, but also a deeper understanding of how the input materials composition descriptors can contribute to its magnitude and/or directionality of the narrowing hysteresis.

Actuating Bimorph Microstructures with Magnetron-Sputtered Ti-Ni-Cu Shape Memory Alloy Films.

The generation of microactuation using narrow thermal hysteresis Ti-Ni-Cu shape-memory alloy films deposited on non-metallic substrates as the active element is studied based on a model previously developed for Ni-Ti/Si bimorphs. To this end, the compositional range in which the B2 (monoclinic) → B19 (orthorhombic) martensitic phase transformation occurs was considered, and films were deposited by magnetron sputtering on heated Si and Kapton substrates. Ultra-fine grains were observed for the 550 °C deposition temperature. The selected composition was close to Ti50Ni35Cu15, so the narrowing of the thermal hysteresis is not associated with a significant reduction in shape recovery capability. The microstructure and composition of the target materials and as-deposited films used in our experiments were characterized by X-ray diffraction and scanning electron microscopy, whereas the temperature dependence of the volume fraction of the martensite phase was derived using differential scanning calorimetry records for the target materials and from the temperature dependence of the electrical resistance data for the films. An original model was used to predict the actuation of cantilever-type bimorphs with Kapton and Si substrates.

Spin-Crossover in a New Iron(II)/Di(pyrazolyl)pyridine Complex with a Terpyridine Embrace Lattice. Thermally Induced Excited Spin State Trapping and Clarification of a Structure–Function Correlation

The complex salts [FeL2]X2 (1X2; L = 2,6-di{4-fluoropyrazol-1-yl}pyridine; X– = BF4– or ClO4–) exhibit abrupt spin-transitions with narrow thermal hysteresis, at T1/2 = 164 K (X– = BF4–) and 148 K (X– = ClO4–). The transition in 1[ClO4]2 is complicated by efficient thermally induced excited spin-state trapping (TIESST) of its high-spin state below ca. 120 K, and the fully low-spin state was achieved only inside the magnetometer at a scan rate of 0.5 K min–1. Crystals of 1[BF4]2 are tetragonal (P421c, Z = 2; phase 1) at 300 K but transform to a highly twinned monoclinic phase 2 (P21, Z = 2) at 285 ± 5 K. These are forms of the “terpyridine embrace” crystal lattice, which often affords cooperative spin-transitions in iron/di(pyrazolyl)pyridine complexes. Phase 2 of high-spin 1[BF4]2 shows a significant temperature dependence by powder diffraction, which reflects increased canting of the monoclinic unit cell as the temperature is lowered. In contrast, 1[ClO4]2 retains phase 2 between 100 and 300 K, and was crystallographically characterized in its thermally trapped metastable high-spin state at 100 K, as well as its thermodynamic high- and low-spin forms at higher temperatures. The spin-crossover transition temperature in 1[ClO4]2 and related compounds correlates well with a parameter describing angular changes to the metal coordination sphere during the transition but not with other commonly used structural indices. The TIESST metastable high-spin state of 1[ClO4]2 shows no single molecule magnet properties at 2 K.

Room temperature huge magnetocaloric properties in low hysteresis ordered Cu-doped Ni-Mn-In-Co alloys

The reduction of the thermal hysteresis in first order magnetostructural transition is a determining factor to decrease energy losses and to improve the efficiency of magnetocaloric cooling based systems. In this work, a Cu doped NiMnInCo metamagnetic shape memory alloy (MMSMA) exhibiting a narrow thermal hysteresis (around 5 K) at room temperature has been designed. In this alloy, the induced L21 ordering process affects the phase stability in an unusual way compared to that observed in NiMnInCo and other NiMn based alloys. This ordering produces an increase in the Curie temperature of the austenite but hardly affects the martensitic transformation temperatures. As a consequence, the ordering increases the magnetization of the austenite without changing the transformation temperatures, doubles the sensitivity of the transformation to magnetic fields (the Claussius-Clapeyron slope goes from 2.1 to 3.9 K/T), improves the magnetocaloric effect, the reversibility and finally, enhances the refrigeration capacity. In addition, the magnetic hysteresis losses are among the lowest reported in the literature and the effective cooling capacity coefficient RCeff reaches 86 J/Kg for 2 T (15 % higher than those found in Ni-Mn based alloys) and 314 J/Kg for 6 T fields. Therefore, the ordered alloy possesses an excellent combination of low thermal hysteresis and high RCeff, not achieved previously in metamagnetic shape memory alloys near room temperature.

Screening for shape memory alloys with narrow thermal hysteresis using combined XGBoost and DFT calculation

Shape memory alloys (SMAs) are desirable candidates for elastocaloric effect materials, but they all suffer from large thermal hysteresis (Thys). This study analyzes multicomponent TiNi-based SMAs dataset by machine learning (ML) to explore new SMAs with narrow Thys. The second-largest eigenvalue λ2 of the stretch transformation matrix U is added to the original dataset to guide the ML process as a feature. Firstly, λ2 is obtained by first-principles calculations combined with ML. XGBoost Regressor (XGBR) combined with Leave-One-Out Cross-Validation (LOO-CV) is selected from four algorithms for modeling with the highest coefficient of determination R2 of 0.87. The introduction of λ2 improves the performance of the model. The dataset is divided into 15 groups based on different doping elements (such as Hf, Cu, Zr, etc.), among which TiNiCu is the most predictive component with the R2 of 0.89. Over 500 TiNiCu components are randomly generated and predicted Thys. Based on the contour maps created from the prediction results, it is found that Thys is likely to decrease with the increase of Cu doping in general, and minimum Thys occurs when the Cu is about 15 at. %, which is consistent with the existing experimental results. Eventually, a potential Thys minimum (1.2 K) region of TixNiyCuz (58.3%≤x ≤ 58.5%, 26.5%≤y ≤ 27%, 14.8%≤z ≤ 15.3%, x + y + z = 100%) SMA composition is predicted. Our study not only provides a potential selection of narrow Thys TiNi-based SMAs but also indicates combining of XGBoost and DFT calculation is an effective strategy for materials design.

Vanadium oxide thin films with extremely narrow thermal hysteresis loop width were obtained by Ta doping for THz modulation applications

Based on the application potential of VO2 thin film in THz modulation field, only keeping its modulation amplitude is no longer applicable, and the film also needs to have lower phase transition temperature and narrower loop width, etc. In order to solve this problem, and since the high valence ion doping can reduce the phase transition temperature of VO2 films, the effect of Ta5+ doping on the phase transition performance of VO2 films is studied and analyzed in this paper. In this work, based on DC reactive magnetron sputtering technology, un-doped and Ta-doped VO2 films were prepared on high-resistance silicon substrate by two-step method. The microstructure of VO2 films before and after Ta doping was characterized by XPS, XRD and SEM images to assist the study and analysis of the influence of Ta5+ ions on the crystal phase structure of VO2. Finally, when the doping concentration of Ta5+ is 0.71%, the phase transition temperature (TC) of VO2 film decreases to 37.5 °C, the loop width (ΔH) narrows to 1.03 °C, and the optical modulation amplitude is maintained at 64.2%, which makes it more suitable for THz modulator.

Low-field reversible magnetocaloric effect in Co-dopedMn-Cr-Sb alloys

The magnetic phase transition and magnetocaloric effect in the Mn1.89− x Cr0.11Co x Sb ( x =0, 0.04, 0.06) alloys were studied in this work. Results show that the alloys undergo the first-order magneto-elastic phase transition from ferrimagnetic phase to antiferromagnetic phase on cooling, with very narrow thermal hysteresis, i.e., 3–4 K. Co doping cannot only enhance the transformation temperatures of magneto-elastic phase transition, but also avoid the formation of unfavorable MnSb phase. Direct measurements on the adiabatic temperature change ∆ T ad are employed to evaluate the magnetocaloric properties for the studied alloys. Under the field change of 1.5 T, the maximum ∆ T ad up to −1.4 K and the reversible ∆ T ad of −1.2 K can be achieved in the Mn1.85Cr0.11Co0.04Sb alloy. The combination of very small thermal hysteresis and large low-field reversible magnetocaloric effect makes the present alloys very attractive for the potential applications in magnetic refrigeration.

Multi‐Magnetic Properties of a Novel SCO [Fe(3‐OMe‐Sal2trien)][Fe(tdas)2]·CH3CN Salt

The multi‐magnetic salt [Fe(3‐OMe‐Sal2trien)][Fe(tdas)2]·CH3CN (1) has been prepared and fully characterized by a variety of methods. The crystal structure of 1, determined at 150, 297 and 350 K, consists of alternating layers composed by a parallel arrangement of the chains of isolated π–π coupled cation pairs of [Fe(3‐OMe‐Sal2trien)]+ and anion pairs of [Fe(tdas)2]–. The complex magnetic behavior of this salt is consistent with the sum of the contributions from spin‐crossover (SCO) cations and strong antiferromagnetically (AFM) coupled dimeric [Fe(tdas)2]22– anions. The observed gradual thermally induced spin transition (T1/2 = 195 K) is relatable to the cation exhibiting disordering of ethylene (–CH2–CH2–) groups between two conformers with a narrow thermal hysteresis of 6 K. The dc magnetization measurements and 57Fe Mössbauer spectroscopy at room temperature are in excellent agreement between γHS(%) value and ratio of disordering of ethylene groups obtained from X‐ray analysis. Mössbauer spectra at 80 K and 296 K indicate a spin transition between S = 1/2 and S = 5/2 for the iron(III) saltrien‐cation and confirms S = 3/2 for the [FeIII(tdas)2]– anion. The experimental results are supplemented with a theoretical Density Functional Theory (DFT) analysis.

Surfactant-mediated prepared VO2 (M) nanoparticles for efficient solar steam generation

Herein, for the first time, we demonstrated the potential practicability of VO2 (M) as a low cost and stable photoabsorber coated on a piece of poplar wood (W/S8-M) in solar steam generation of Caspian Sea water. The evaporation rate of 3.63 kg m−2 h−1 and the solar steam generation efficiency of 75.60% for W/S8-M were obtained under 3 sun (3 kW m−2) irradiation within 40 min. The concentration of sodium ions in the seawater decreased from 3138.19 to 6.61 mg L−1 for W/S8-M which is far below the drinking water standards. The pH and electrical conductivity of seawater was decreased after desalination by W/S8-M to a large extent. A surfactant-mediated method using different amounts of cetyltrimethylammonium bromide (CTAB) was used to prepare VO2 (M). It was revealed that the sample prepared by addition of 0.08 g CTAB using hydrothermal method has the smallest particle size of 230 nm, the largest specific surface area of 14.542 m2 g-1, the greatest mean pore size of 43.53 nm, narrow thermal hysteresis width of 4.12 °C, and the lowest semiconductor–metal phase transition temperature of 65.23 °C. For the first time, the ATR-FTIR spectroscopy was used to monitor the SMT of VO2 (M) at different temperatures. We found that the samples have the same unique ATR-FTIR spectra below Tc with the characteristic band at 835 and a shoulder at 1020 cm−1 while at T > Tc, the fairly linear curves without any meaningful band are appeared.

Effect of chemical ordering annealing on superelasticity of Ni–Mn–Ga–Fe ferromagnetic shape memory alloy microwires**Project supported by the National Natural Science Foundation of China (Grant Nos. 51701099, 51801044, and 51671071), the Natural Science Foundation of Heilongjiang Province of China (Grant No. LH2019E091), and Fundamental Research Funds in Heilongjiang Provincial Universities, China (Grant No. 135409320). Thanks to the help of Technology Innovation

Ni50Mn25Ga20Fe5 ferromagnetic shape memory alloy microwires with diameters of ∼ 30–50 μm and grain sizes of ∼ 2–5 μm were prepared by melt-extraction technique. A step-wise chemical ordering annealing was carried out to improve the superelasticity strain and recovery ratio which were hampered by the internal stress, compositional inhomogeneity, and high-density defects in the as-extracted Ni50Mn25Ga20Fe5 microwires. The annealed microwires exhibited enhanced atomic ordering degree, narrow thermal hysteresis, and high saturation magnetization under a low magnetic field. As a result, the annealed microwire showed decreased superelastic critical stress, improved reversibility, and a high superelastic strain (1.9%) with a large recovery ratio (> 96%). This kind of filamentous material with superior superelastic effects may be promising materials for minor-devices.

Tuning the Reversible Magnetocaloric Effect in Ni–Mn–In‐Based Alloys through Co and Cu Co‐Doping

AbstractThe reversibility of the giant magnetocaloric effect (MCE) through the magnetic field–induced magnetostructural transformation in Ni–Mn–In‐based alloys is a key issue towards the potential magnetic refrigeration applications. In this work, Co and Cu are simultaneously doped to tune the reversible magnetocaloric properties associated with the magnetostructural transformation. Owing to the integration of large magnetization difference ΔM, suitable transformation entropy ΔStr, and narrow thermal hysteresis ΔThys in a Ni46Co3Mn35Cu2In14 alloy, the reversible field–induced inverse martensitic transformation is realized in a wide temperature range of 30 K under the field of 5T, yielding a maximum reversible magnetic entropy change ΔSMmax of 16.4 J kg−1 K−1. Moreover, under a low field change of 1.5T, a large reversible adiabatic temperature variation ΔTad of 2.5 K is also obtained, representing the highest value so far under the low field change of 1.5T in Ni–Mn‐based alloys. It is demonstrated that multi‐component alloying by combining the effects of appropriate substitutional elements is an effective way to develop high‐performance magnetocaloric materials.

VO2(A) nanorods: One-pot synthesis, formation mechanism and thermal transformation to VO2(M)

The monoclinic VO2(M) has promising applications in intelligent devices but its preparation still requires improvement to permit cost-effective mass production. In this work, we report a 2-stage approach for producing VO2(M) nanorods by (1) hydrothermal reduction of vanadium pentoxide by sodium bisulfate at 220 °C to form VO2(A), and (2) subsequent thermal activated phase transformation of VO2(A) to VO2(M) at 350–450 °C in vacuum. The obtained VO2(M) nanorods showed a reversible phase transition temperature at about 62.5 °C and a narrow thermal hysteresis width of 10 °C. The mechanism of the hydrothermal reduction was studied by combined ex situ microscopic and diffraction characterization of cooled samples as well as in situ PXRD experiments, in which the hydrothermal synthesis was monitored in real time by time-resolved diffraction datasets. It was found that the hydrothermal synthesis of VO2(A) is a 4-step process: (1) reduction of V2O5 to form VO2(B) nanoparticles, (2) oriented attachment of VO2(B) nanoparticles along the [110] direction, (3) formation of VO2(B) nanorods as a results of oriented attachments, and (4) hydrothermal transformation of the metastable intermediate VO2(B) nanorods to VO2(A) nanorods. This clear understanding of the mechanism will help the further optimization of synthesis temperature and time for preparing VO2(A). This method provides a low temperature thermal treatment alternative and hence helps the reduction of cost for the production of VO2(M), bring the mass application of VO2(M) one step closer.

On the influence of thermal hysteresis on the performance of thermomagnetic motors

Although thermal hysteresis might be a problem in the magnetocaloric refrigeration, the same is not necessarily true for thermomagnetic motor applications. This work presents a comparison of the magnetocaloric properties of materials with first order magnetic transition (having large or narrow thermal hysteresis) to those with second order magnetic transition, assessing the application of these materials in thermomagnetic motors through a thermodynamic approach. Results show that the larger the thermal hysteresis, the higher the specific work produced in a thermal cycle. This allows operation at higher temperature differences with high efficiency relative to Carnot efficiency, when compared with systems using narrow hysteresis and second order transition materials.

Spatiotemporal dynamics of the spin transition in[Fe(HB(tz)3)2]single crystals

The spatiotemporal dynamics of the spin transition have been thoroughly investigated in single crystals of the mononuclear spin-crossover (SCO) complex $[\mathrm{Fe}(\mathrm{HB}(\mathrm{tz}{)}_{3}{)}_{2}]$ ($\mathrm{tz}=1,2$,4-triazol-1-yl) by optical microscopy. This compound exhibits an abrupt spin transition centered at 334 K with a narrow thermal hysteresis loop of $\ensuremath{\sim}1$ K (first-order transition). Most single crystals of this compound reveal exceptional resilience upon repeated switching (several hundred cycles), which allowed repeatable and quantitative measurements of the spatiotemporal dynamics of the nucleation and growth processes to be carried out. These experiments revealed remarkable properties of the thermally induced spin transition: high stability of the thermal hysteresis loop, unprecedented large velocities of the macroscopic low-spin/high-spin phase boundaries up to 500 \textmu{}m/s, and no visible dependency on the temperature scan rate. We have also studied the dynamics of the low-spin \ensuremath{\rightarrow} high-spin transition induced by a local photothermal excitation generated by a spatially localized ($\O{}=2\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$) continuous laser beam. Interesting phenomena have been evidenced both in quasistatic and dynamic conditions (e.g., threshold effects and long incubation periods, thermal activation of the phase boundary propagation, stabilization of the crystal in a stationary biphasic state, and thermal cutoff frequency). These measurements demonstrated the importance of thermal effects in the transition dynamics, and they enabled an accurate determination of the thermal properties of the SCO compound in the framework of a simple theoretical model.

Functional fatigue of submicrometer NiTi shape memory alloy thin films

Submicrometer NiTi alloy thin films prepared using biased target ion beam deposition (BTIBD) recently revealed ultranarrow thermal hysteresis and a B2 ⇌ R-phase transformation path. Here, the authors investigate the influence of thermal cycles on the phase transformation characteristics of near-equiatomic NiTi alloy films with 800 nm thicknesses deposited using BTIBD. Evolution of transformation temperatures, thermal hysteresis, and recovery stress over thermal cycles is tracked using the wafer curvature method, and changes in atomic crystal structures are detected using x-ray diffraction. The authors find that the submicrometer thin films exhibit stabilized transformation temperatures, consistent recovery stresses, and reproducible narrow thermal hysteresis over up to 100 cycles although Ni49.7Ti50.3 films undergo two-stage phase transformation B2 → R-phase → B19′ while Ni50.3Ti49.7 films have one-stage transformation between the B2 and R-phases. The inherent deposition mechanism and transformation-path-related lattice distortion can be responsible for the reduced fatigue of functional characteristics in submicrometer NiTi alloy thin films.

Narrow thermal hysteresis of NiTi shape memory alloy thin films with submicrometer thickness

NiTi shape memory alloy (SMA) thin films were fabricated using biased target ion beam deposition (BTIBD), which is a new technique for fabricating submicrometer-thick SMA thin films, and the capacity to exhibit shape memory behavior was investigated. The thermally induced shape memory effect (SME) was studied using the wafer curvature method to report the stress-temperature response. The films exhibited the SME in a temperature range above room temperature and a narrow thermal hysteresis with respect to previous reports. To confirm the underlying phase transformation, in situ x-ray diffraction was carried out in the corresponding phase transformation temperature range. The B2 to R-phase martensitic transformation occurs, and the R-phase transformation is stable with respect to the expected conversion to the B19′ martensite phase. The narrow hysteresis and stable R-phase are rationalized in terms of the unique properties of the BTIBD technique.

Crystal size induced reduction in thermal hysteresis of Ni-Ti-Nb shape memory thin films

Ni41.7Ti38.8Nb19.5 shape memory alloy films were sputter-deposited onto silicon substrates and annealed at various temperatures. A narrow thermal hysteresis was obtained in the Ni-Ti-Nb films with a grain size of less than 50 nm. The small grain size, which means an increase in the volume fraction of grain boundaries, facilitates the phase transformation and reduces the hysteresis. The corresponding less transformation friction and lower heat transfer during the shear process, as well as reduced spontaneous lattice distortion, are responsible for this reduction of the thermal hysteresis.

Effect of platinum substitution on the structural and magnetic properties ofNi2MnGaferromagnetic shape memory alloy

${\mathrm{Ni}}_{2}\mathrm{MnGa}$ exhibits ideal ferromagnetic shape memory properties, however, brittleness and a low-temperature martensite transition hinder its technological applications motivating the search for novel materials showing better mechanical properties as well as higher transition temperatures. In this work, the crystal structure, phase transitions, and the magnetic properties of quaternary ${\mathrm{Ni}}_{2\ensuremath{-}x}{\mathrm{Pt}}_{x}\mathrm{MnGa}(0\ensuremath{\le}x\ensuremath{\le}1)$ shape memory alloys were studied experimentally by x-ray diffraction, magnetization measurements, and neutron diffraction and compared to ab initio calculations. Compositions within $0\ensuremath{\le}x\ensuremath{\le}0.25$ exhibit the cubic austenite phase at room temperature. The $x\ensuremath{\approx}0.3$ composition exhibits a seven-layer modulated monoclinic martensite structure. Within $0.4\ensuremath{\le}x\ensuremath{\le}1$, the system stabilizes in the nonmodulated tetragonal structure. The martensite transition has very narrow thermal hysteresis $0\ensuremath{\le}x\ensuremath{\le}0.3$, which is a typical characteristic of a shape memory alloy. By increasing $x$, the temperature of the martensite transition increases, while that of the magnetic transition decreases. The $x=1$ composition ($\text{NiPtMnGa}$) in the martensite phase undergoes a para-to-ferrimagnetic transition. The saturation magnetization exhibits a nontrivial behavior with increasing up to $x\ensuremath{\approx}0.25$, above which, it suddenly decreases. Powder neutron diffraction reveals the presence of antisite disorder, with about 17% of the original Ga sites being occupied by Mn. Computations suggest that the antisite disorder triggers an antiferromagnetic coupling between two Mn atoms in different crystallographic positions, resulting into a sudden drop of the saturation magnetization for higher $x$.