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钙钛矿锰氧化物具备磁热效应高、性能稳定可控、成本低廉等显著优点, 是适用于室温磁制冷领域的优质候选工质材料之一. 但该体系内部电磁学性质复杂, 特别是关于铁磁相互作用机制和磁相变性质等关键科学问题仍然有待深入探索. 分析磁相变临界行为有利于揭示磁性材料内部的铁磁相互作用距离和机制等重要信息. 本文简要介绍了钙钛矿锰氧化物相关理论背景以及各种磁相变临界行为分析方法, 随后归纳了近年来多种钙钛矿锰氧化物的磁相变临界行为研究, 系统对比了不同带宽典型锰氧化物在单晶和多晶形态下的磁相变临界行为, 讨论了A/B位掺杂不同元素以及不同制备工艺条件对其临界参数的影响, 对其中渡越于一级和二级相变的La-Ca-Mn-O体系在不同磁场范围下的临界参数演化进行了讨论. 最后对处于磁相变三重临界点附近的部分锰氧化物材料的磁热效应研究进行了总结和展望.Hole-doped perovskite-type manganites have received intensive attention due to their intriguing physical phenomena such as giant magnetocaloric effect and magnetic-phase transitions. However, the mechanism of internal ferromagnetic interaction still needs to be further explored due to the complex natures of competing double-exchange (DE) and super-exchange (SE) interaction, Jahn-Teller (JT) polaron localization, charge ordering, and phase separation scenarios. Critical exponent analysis near magnetic phase transition is a powerful tool to investigate the details of the ferromagnetic interactions and has been used frequently in various magnetocaloric materials. In this article, the critical behavior analyses of perovskite manganites in recent years are comprehensively reviewed. A large number of studies have shown that even in single-phase materials with uniform structure and composition, the critical behavior can be affected by multiple factors such as grain boundary density and the degree of disorder, making them difficult to fully describe the intrinsic ferromagnetism. In this review, firstly, the critical behaviors of typical manganites with different bandwidths in single crystal and polycrystalline are discussed. In a double-exchange dominated system such as La-Sr-Mn-O, short-range 3D-Heisenberg model is basically in good accordance with optimally-doped single crystal sample. However, it would be replaced by long-range mean-field critical behavior in polycrystalline sample when the correlation length exceeds the crystallite size. In a typical intermediate bandwidth system such as La-Ca-Mn-O exhibiting a complex phase diagram described by competing SE/DE interactions, JT polaron localization/delocalization, and Griffith phase disorder, the critical exponent can vary from 3D-Heisenberg model to tricritical mean-field model, for the crossover from first to second order phase transition. Secondly, the studies of elements doping and different fabrication methods indicate that the critical behavior of manganites can be effectively modulated, and vary between different theoretical models including even nonuniversal exponent for highly disordered magnetic system. In the following part, the influence of magnetic field on the critical behavior and field induced crossover phenomena of La-Ca-Mn-O system near tricritical point is analyzed and discussed in detail. Furthermore, the magnetocaloric effects of materials near the tricritical point collected in many studies are listed and compared with each other. Excellent magnetocaloric properties with high magnetic entropy change and relative cooling power in plenty of researches indicate that ideal magnetocaloric material would be very likely to be found in the materials near the tricritical point, which lay at the borderline between first-order and second-order phase transition. Consequently, it is suggested that perovskite manganites are still quite promising in the potential magnetic refrigeration applications, and need to be further developed.
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Material Technique β γ δ Model Ref. La0.7Ba0.3MnO3SC MAP 0.35 1.41 5.5 3D-Heisenberg [26] La0.7Ba0.3MnO3PC MAP 0.493 1.059 3.15 Mean-field [27] La0.67Ba0.33MnO3PC MAP 0.464 1.29 3.78 Mean-field/3D-Heisenberg [28] La0.7Sr0.3MnO3SC MAP 0.37 1.22 4.25 close to 3D-Heisenberg [29] La0.75Sr0.25MnO3SC MAP 0.4 1.27 4.12 Mean-field/3D-Ising [30] La0.8Sr0.2MnO3PC MAP 0.5 1.08 3.13 Mean-field [31] La0.875Sr0.125MnO3SC MAP 0.37 1.38 4.72 3D-Heisenberg [32] La0.6Ca0.4MnO3PC MAP 0.25 1.03 5 Tricritical-Mean-field [33] La0.79Ca0.21MnO3SC MAP 0.09 1.71 20 nonuniversal [34] La0.8Ca0.2MnO3SC MAP 0.374 1.382 4.779 3D-Heisenberg [35] La0.82Ca0.18MnO3SC MAP 0.374 1.379 4.783 3D-Heisenberg [35] Nd0.6Sr0.4MnO3SC KF 0.308 1.172 4.75 3D-Ising [36] Nd0.6Sr0.4MnO3PC MAP 0.51 1.01 3.13 Mean-field [37] Nd0.67Sr0.33MnO3PC MAP 0.23 1.05 5.13 Tricritical-Mean-field [37] Nd0.7Sr0.3MnO3PC MAP 0.271 0.922 4.4 Tricritical-Mean-field [38] Pr0.6Sr0.4MnO3SC KF 0.312 1.106 4.545 3D-Ising [36] Pr0.6Sr0.4MnO3SC MAP 0.365 1.309 4.648 3D-Heisenberg [39] Pr0.6Sr0.4MnO3PC MAP 0.276 0.918 4.325 Tricritical-Mean-field [40] KF 0.273 1.001 4.325 Pr0.71Ca0.29MnO3SC MAP 0.37 1.38 4.62 3D-Heisenberg [41] Pr0.71Ca0.29MnO3PC MAP 0.521 0.912 2.71 Mean-field [42] Pr0.73Ca0.27MnO3SC MAP 0.36 1.36 4.81 3D-Heisenberg [41] Pr0.73Ca0.27MnO3PC MAP 0.362 1.132 4.09 3D-Heisenberg [42] 注: SC表示单晶; PC表示多晶. Material Technique β γ δ Model Ref. La0.67(Ca0.5Ba0.5)0.33MnO3 MAP 0.402 1.110 3.761 Mean-field/3D-Heisenberg [28] La0.7Ca0.15Ba0.15MnO3 MAP 0.438 1.032 3.360 Mean-field [27] La0.7Ca0.2Ba0.1MnO3 MAP 0.284 0.909 4.200 Tricritical-Mean-field/3D-Ising [43] KF 0.297 0.925 4.110 La0.7Ca0.15Sr0.15MnO3 MAP 0.491 1.054 3.150 Mean-field [27] La0.7Ca0.1Sr0.2MnO3 KF 0.360 1.220 4.400 3D-Heisenberg [44] La0.7Ca0.2Sr0.1MnO3 KF 0.260 1.060 5.100 Tricritical-Mean-field [44] La0.69Dy0.01Ca0.3MnO3 MAP 0.230 0.920 5.000 Tricritical-Mean-field [45] KF 0.250 0.870 4.480 La0.7Ca0.28Sn0.02MnO3 KF 0.218 0.858 4.936 Tricritical-Mean-field [46] La0.7Ca0.26Sn0.04MnO3 KF 0.467 1.095 3.345 Mean-field [46] La0.75Dy0.05Sr0.2MnO3 MAP 0.266 0.920 4.460 Tricritical-Mean-field [47] KF 0.272 0.931 4.420 La0.1Nd0.6Sr0.3MnO3 MAP 0.248 1.066 5.170 Tricritical-Mean-field [48] KF 0.257 1.120 5.170 Pr0.4Sm0.15Sr0.45MnO3 KF 0.324 1.212 4.812 3D-Ising [49] Pr0.3Sm0.25Sr0.45MnO3 KF 0.255 0.957 5.105 Tricritical-Mean-field [49] La0.57Nd0.1Sr0.33MnO3 MAP 0.356 1.152 4.235 3D-Heisenberg [50] KF 0.368 1.191 4.236 La0.57Nd0.1Sr0.28□0.05MnO3 MAP 0.312 1.173 4.760 3D-Ising [50] KF 0.326 1.183 4.619 Pr0.6Sr0.4MnO3 MAP 0.276 0.918 4.325 Tricritical-Mean-field [40] KF 0.273 1.001 4.325 Pr0.6Sr0.3□0.1MnO3 MAP 0.253 0.987 4.890 Tricritical-Mean-field [40] KF 0.242 0.945 4.890 Pr0.5□0.1Sr0.4MnO3 MAP 0.323 1.113 4.446 3D-Ising [40] KF 0.325 1.092 4.446 注: □表示离子空位. Material Technique β γ δ Model Ref. La0.67Ba0.33Mn0.98Ti0.02O3 MAP 0.537 1.015 2.890 Mean-field [51] KF 0.551 1.020 2.851 La0.67Ba0.33Mn0.95Fe0.05O3 KF 0.504 1.013 3.040 Mean-field [52] La0.7Ba0.3Mn0.95Ti0.05O3 MAP 0.374 1.228 4.260 3D-Heisenberg [53] La0.7Ba0.3Mn0.9Ti0.1O3 MAP 0.339 1.307 4.780 3D-Ising [53] La0.8Ba0.2Mn0.8Fe0.2O3 MAP 0.365 1.227 4.362 3D-Heisenberg [54] KF 0.318 1.159 4.645 La0.67Sr0.33Mn0.9Fe0.1O3 MAP 0.450 1.240 3.740 Mean-field/3D-Heisenberg [55] KF 0.538 1.330 3.470 La0.7Sr0.3Mn0.95Al0.05O3 KF 0.458 1.001 3.185 Mean-field [56] La0.7Sr0.3Mn0.95Ti0.05O3 KF 0.344 1.149 4.340 Mean-field/3D-Heisenberg [56] La0.7Sr0.3Mn0.9Co0.1O3 KF 0.457 1.114 3.440 Mean-field/3D-Heisenberg [57] La0.7Sr0.3Mn0.99Ni0.01O3 MAP 0.394 1.092 3.990 Mean-field/3D-Heisenberg [58] La0.7Sr0.3Mn0.98Ni0.02O3 MAP 0.400 1.082 3.790 Mean-field/3D-Heisenberg [58] La0.7Sr0.3Mn0.97Ni0.03O3 MAP 0.468 1.010 2.670 Mean-field [58] La0.7Sr0.3Mn0.98Cu0.02O3 KF 0.464 1.162 3.546 close to Mean-field [59] La0.7Sr0.3Mn0.96Cu0.04O3 KF 0.449 1.202 3.681 close to Mean-field [59] La0.67Ca0.33Mn0.9Cr0.1O3 MAP 0.555 1.170 2.710 Mean-field [60] La0.67Ca0.33Mn0.75Cr0.25O3 MAP 0.680 1.090 2.936 close to Mean-field [60] La0.67Ca0.33Mn0.9Ga0.1O3 MAP 0.380 1.365 4.590 3D-Heisenberg [61] KF 0.387 1.362 4.520 La0.7Ca0.3Mn0.95Ti0.05O3 KF 0.601 1.171 2.950 Mean-field [62] La0.7Ca0.3Mn0.9Ti0.1O3 KF 0.389 1.403 4.400 3D-Heisenberg [62] La0.7Ca0.3Mn0.91Ni0.09O3 MAP 0.171 0.976 6.700 Tricritical-Mean-field [63] La0.7Ca0.3Mn0.88Ni0.12O3 MAP 0.262 0.978 4.700 Tricritical-Mean-field [63] La0.7Ca0.3Mn0.85Ni0.15O3 MAP 0.320 0.990 4.100 3D-Ising [63] La0.7Ca0.3Mn0.95Cu0.05O3 MAP 0.490 1.040 3.120 Mean-field [64] La0.7Ca0.3Mn0.9Zn0.1O3 MAP 0.474 1.152 3.430 Mean-field [65] La0.8Ca0.2Mn0.9Co0.1O3 MAP 0.204 1.969 11.983 nonuniversal [66] KF 0.123 1.351 11.983 La0.8Ca0.2Mn0.8Co0.2O3 MAP 0.401 1.332 4.321 3D-Heisenberg [66] KF 0.418 1.303 4.321 Nd0.67Sr0.33Mn0.9Cr0.1O3 MAP 0.337 0.784 3.326 nonuniversal [67] Nd0.67Sr0.33Mn0.9Fe0.1O3 MAP 0.436 0.94 3.156 Mean-field [67] Nd0.67Sr0.33Mn0.9Co0.1O3 MAP 0.431 0.929 3.155 Mean-field [67] Pr0.67Sr0.33Mn0.95Al0.05O3 MAP 0.381 1.323 4.635 3D-Heisenberg [68] KF 0.381 1.320 4.635 Pr0.67Sr0.33Mn0.9Al0.1O3 MAP 0.374 1.333 4.667 3D-Heisenberg [68] KF 0.377 1.331 4.667 Material Technique β γ δ Model Ref. La0.6Sr0.4MnO3SG/800 ºC KF 0.560 1.140 3.035 close to Mean-field [69] La0.6Sr0.4MnO3SG/1100 ºC KF 0.480 1.052 3.190 Mean-field [69] La0.6Sr0.4MnO3SS KF 0.530 1.110 3.094 Mean-field [69] La0.67Sr0.33MnO3SS MAP 0.333 1.325 4.978 3D-Heisenberg [70] La0.67Sr0.33MnO3SG MAP 0.500 1.150 3.290 Mean-field [55] KF 0.479 1.260 3.630 La0.7Ba0.1Ca0.1Sr0.1MnO3WM MAP 0.448 1.148 3.563 Mean-field [71] KF 0.476 1.029 3.096 La0.7Ba0.1Ca0.1Sr0.1MnO3SG MAP 0.235 1.153 5.906 Tricritical-Mean-field [71] KF 0.262 1.165 5.447 La0.7Ca0.2Ba0.1MnO3BM MAP 0.265 0.867 4.271 Tricritical-Mean-field [72] KF 0.261 0.988 4.386 La0.7Ca0.2Ba0.1MnO3SS MAP 0.284 0.909 4.200 Tricritical-Mean-field/3D-Ising [43] KF 0.297 0.925 4.110 La0.7Ca0.2Sr0.1MnO3BM MAP 0.397 0.966 3.430 3D-Heisenberg [73] La0.7Ca0.2Sr0.1MnO3SS MAP 0.276 0.966 4.500 Tricritical-Mean-field [74] KF 0.315 0.954 4.028 La0.7Ca0.2Sr0.1MnO3SG MAP 0.484 1.037 3.143 Mean-field [74] KF 0.469 1.013 3.160 La0.7Ca0.3MnO3BM/40 nm MAP 0.485 1.051 3.100 Mean-field [75] La0.7Ca0.3MnO3BM/16 nm MAP 0.621 0.825 2.200 nonuniversal La0.7Ca0.3MnO3SG MAP 0.240 1.010 3.090 Tricritical-Mean-field [76] La0.75Ca0.25MnO3SG MAP 0.521 0.94 2.804 Mean-field [77] KF 0.529 0.939 2.775 La0.8Ca0.2MnO3SG MAP 0.505 1.004 3.060 Mean-field [78] KF 0.499 1.007 3.060 Nd0.7Ca0.15Sr0.15MnO3BM/4 h KF 0.243 0.907 4.540 Tricritical-Mean-field [79] Nd0.7Ca0.15Sr0.15MnO3BM/24 h KF 0.311 1.100 4.130 3D-Ising [79] Pr0.6Ca0.1Sr0.3Mn0.975Fe0.025O3SS MAP 0.644 1.075 2.763 Mean-field [80] KF 0.622 1.097 2.763 Pr0.6Ca0.1Sr0.3Mn0.975Fe0.025O3SG MAP 0.357 1.292 4.290 3D-Heisenberg [80] KF 0.370 1.220 4.290 Pr0.8Sr0.2MnO3SG MAP 0.260 0.978 4.760 Tricritical-Mean-field [81] KF 0.260 0.993 4.810 Pr0.8Sr0.2MnO3SS MAP 0.318 1.260 4.960 3D-Ising [82] KF 0.326 1.246 4.960 注: SS表示固相反应法; SG表示溶胶凝胶法(附烧结温度工艺条件); WM表示湿混法; BM表示球磨法(附平均粒径尺寸或球磨时间等工艺条件). Material Field range Technique β γ δ Model Ref. La0.6Ca0.4MnO3 1—2 T KF 0.249 1.008 5.043 Tricritical-Mean-field [83] 2—3 T KF 0.255 0.857 4.359 crossover 3—4 T KF 0.262 0.833 4.18 crossover 4—5 T KF 0.267 0.797 3.983 crossover 5—6 T KF 0.263 0.776 3.954 close to Tricritical-Mean-field La0.8Ca0.2MnO3 1—2 T KF 0.349 1.231 4.524 3D-Heisenberg/Ising [83] 2—3 T KF 0.316 1.081 4.421 crossover 3—4 T KF 0.281 0.992 4.534 crossover 4—5 T KF 0.272 0.91 4.341 crossover 5—6 T KF 0.259 0.918 4.552 Tricritical-Mean-field La0.7Ca0.275Ba0.025MnO3 2—3 T MAP 0.209 — — Tricritical-Mean-field [84] 3—4 T MAP 0.218 1.098 6.04 4—5 T MAP 0.227 1.06 5.67 La0.7Ca0.25Ba0.05MnO3 1—2 T MAP 0.221 — — Tricritical-Mean-field [84] 2—3 T MAP 0.225 1.052 5.68 3—4 T MAP 0.235 1.012 5.31 4—5 T MAP 0.249 1.022 5.1 La0.7Ca0.225Ba0.075MnO3 1—2 T MAP 0.216 0.973 5.5 Tricritical-Mean-field [84] 2—3 T MAP 0.224 0.982 5.38 3—4 T MAP 0.238 1.016 5.27 4—5 T MAP 0.253 0.992 4.92 La0.7Ca0.2Ba0.1MnO3 1—2 T MAP 0.301 1.382 5.59 Tricritical-Mean-field/3D-Ising [84] 2—3 T MAP 0.312 1.38 5.42 3D-Ising 3—4 T MAP 0.322 1.381 5.29 3D-Ising 4—5 T MAP 0.326 1.342 5.12 3D-Ising La0.7Ca0.3MnO3 10—14 T MAP 0.252 1.005 — Tricritical-Mean-field [85] Material TC/K ΔH/ T –ΔSM/(J·kg–1·K–1) RCP/(J·kg–1) Ref. La0.7Ba0.2Ca0.1MnO3SG 350 2 2.35 70 [87] 5 5.80 167 La0.7Ba0.2Ca0.1Mn0.95Al0.05O3SG 321 2 2.12 85 [87] 5 5.30 180 La0.7Ba0.2Ca0.1Mn0.9Al0.1O3SG 300 2 1.86 96 [87] 5 4.60 193 La0.7Ca0.3MnO3SS 255 1 4.52 45.2 [46] La0.7Ca0.28Sn0.02MnO3SS 200 1 2.79 55.8 [46] La0.7Ca0.26Sn0.04MnO3SS 167 1 1.58 69.5 [46] La0.69Dy0.01Ca0.3MnO3SS 246 5 14.94 100.24 [45] La0.6Ca0.3Ag0.1MnO3SS 256 2 3.89 55.51 [88] 5 6.95 179.78 La0.6Ca0.3Ag0.1MnO3SG 270 2 5.55 84.46 [88] 5 8.67 230.35 La0.6Ca0.3Sr0.1MnO3SG 304 2 2.89 98.17 [89] 5 5.26 262.53 La0.7Ca0.2Sr0.1MnO3SS 284 3 4.30 150 [90] La0.7Ca0.2Sr0.1MnO3BM 297 1 1.47 54.4 [73] La0.7Ca0.19Sr0.11MnO3BM 301 1 1.42 52.5 [73] La0.7Ca0.18Sr0.12MnO3BM 309 1 1.38 44.2 [73] La0.7Ca0.27Na0.03MnO3SS 260 4 8.10 232 [91] La0.7Ca0.24Na0.06MnO3SS 263 4 7.00 234 [91] La0.7Ca0.21Na0.09MnO3SS 271 4 6.90 236 [91] La0.7Ba0.1Ca0.1Sr0.1MnO3WM 315 2 1.34 102.51 [71] 5 3.16 284.53 La0.7Ba0.1Ca0.1Sr0.1MnO3SG 330 2 2.58 74.92 [71] 5 4.89 229.29 La0.8Na0.2Mn0.97Bi0.03O3SS 320 5 4.77 218 [92] La0.8Na0.2Mn0.97Bi0.03O3SG 257 5 5.88 252 [92] La0.4Pr0.3Ca0.1Sr0.2MnO3SS 289 2 3.08 83.3 [86] La0.6Gd0.1Sr0.3Mn0.8Si0.2O3SG 271 5 5.35 180 [93] La0.7Bi0.05Sr0.15Ca0.1Mn0.95In0.05O3SG 310 5 6.00 258 [94] 注: 1) 表中符号含义如下:TC为居里温度; ΔH为磁场变化范围; –ΔSM为最大磁熵变值; RCP为相对制冷能力, 由磁熵变曲线的峰值与半峰宽数值相乘而得; 2) SS表示固相反应法; SG表示溶胶凝胶法; WM表示湿混法; BM表示球磨法. -
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