Deposition Conditions

The deposition conditions (oxygen pressure PO2, deposition temperature TS, laser fluence, ...) can drastically influence the properties [45,46]. For Nd07Sr03MnO3 grown on (100)-LaAlO3 [47], the maximum resistivity peak shifts to lower temperatures as the deposition temperature decreases (the optimum TC of 175 K is obtained for TS = 615 °C). Yamada et al. [21] have shown that the TIM decreases with either TS or PO2 in La1-xPbxMnO3. The deposition temperature also strongly influences the microstructure of Pra7Sra3MnO3, since films grown at low temperature exhibit a columnar growth with well-connected grains while those deposited at higher temperature are poorly connected with plateletlike crystals [45].

In addition, it has also been shown that in-situ [48] or ex-situ [49] oxygen annealing is necessary to obtain the optimized properties. In particular, the postannealing of the films can lead to significant modification of the oxygen content and optimizes the physical properties [50] such as T!M [47], TC, and the CMR effect [1,3,5]. This annealing effect is necessary to achieve the optimum oxygen concentration of the films. Depending on the nature of the film and on the growth conditions, annealing is used either to fully oxidize the film (oxidative annealing) or to remove extra oxygen (reductive annealing). The effect of annealing was also observed in films annealed in N2 atmosphere [51]. The T!M transition shifts after the annealing to higher temperature and the MR ratio increases slightly. The magnetic transition also occurs at higher temperature after annealing. For example, the Curie temperature, TC, is found to increase from 200 K for as-deposited La0 8MnO3 film to 320 K after the fourth thermal treatment (see Fig. 2) [50]. In fact, the changes under annealing can also be seen on the position of the diffraction peak [41]: the out-of-plane parameter decreases, which relates to an increase of the Mn3+/Mn4+ ratio [15,50]. This annealing effect can lead to an improvement in physical properties (like in La0 8Ca0 2MnO3 where the T!M value is higher than that of the bulk [52]) but sometimes the resistivity peak is lower by more than 100 K [53]. In fact, Prellier et al. have shown that the entire phase diagram (see Fig. 3) is different in the ferromagnetic region of La1-xCaxMnO3 (0 < x < 0.5) [15] as compared to the bulk (in terms of transport and magnetic transitions).

Doping is another method used to improve the magnetic properties. For example, enhancement of the properties (T!M and TC) is observed with silver addition to the La07Ca03MnO3 target (5 wt%) [54] or with La2/3Sr1/3MnO3 films doped with Ag and grown by dual-beam PLD [55].

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