General synthesis of rare-earth orthochromites with quasi-hollow nanostructures and their magnetic properties

Abstract

Rare-earth orthochromites are extremely interesting because of their potential applications as multifunctional materials. However, it is still a great challenge for the general synthesis of nanostructured full rare-earth orthochromites series. Here, a facile and versatile solvothermal reduction strategy is successfully employed in the preparation of rare-earth chromites with quasi-hollow nanostructures. X-ray diffraction data show that all the products have the orthorhombic perovskite structure. The electron microscopy analysis reveals that the morphology of the product is seriously affected by the rare-earth ionic radius. Tube-like and vesicle-like structures can be formed for the larger and smaller rare-earth cationic radii, respectively. The experimental results suggest that the roomtemperature precursors of potassium rare-earth chromates serve as a self-template for the in situ reduction and formation of rare-earth orthochromites hollow structures. The magnetization studies demonstrate that all the products, as it would be expected, undergo a magnetic transition from paramagnetic to antiferromagnetic phase at the Néel temperature (T N1 ) attributed to Cr 3+ -Cr 3+ exchange and this critical temperature goes up linearly with an increase in the rare-earth ionic radius.Additionally, some samples exhibit a variety of fancy magnetic properties, including thermal hysteresis suggesting a first-order magnetic transition, magnetization reversal due to the antiparallel polarization of the R 3+ paramagnetic moments by the Cr 3+ canted antiferromagnetic ones, and magnetic exchange bias related to the spin reorientation transition of the Cr 3+ magnetic moments. † Electronic supplementary information (ESI) available: XRD patterns and SEM images of the typical room-temperature intermediates; TEM images of the typical 1200 C annealing sample; SEM images of LaCrO 3 , PrCrO 3 , NdCrO 3 and SmCrO 3 before and aer annealing; summary of the magnetic data based on the temperature dependence of the magnetization for all samples. See

Zero-field cooled exchange bias effect in La Sm1−CrO3 (x=0–0.9) ceramics

“…The strength of some peaks gradually weakens from x ¼0 to x ¼0.9 with increasing the concentration of La 3 þ , e.g. the strength of (020), (200), (211), and (122) peaks, and these peaks disappear when the value of x exceeds 0.5, which results from the change in iron radii as the radii of La 3 þ is larger than that of Sm 3 þ [10,11,13]. Typical Rietveld analysis results for SmCrO 3 and La 0.5 Sm 0.5 CrO 3 are shown in Fig.…”

“…Below the spin reorientation transition temperature (T SR ), the weak FM moment generates an internal field (H I ) at the R 3 þ site [28]. Due to the paramagnetic effect of magnetic R 3 þ , the antiparallel coupling between R 3 þ and Cr 3 þ sometimes brings about spin reorientation [10][11][12][13][14][15], negative magnetization [16][17][18][19], and EB effects [20][21][22][23]. By changing the magnitude of external magnetic field, tunable magnetic behavior can be obtained.…”

“…Recently, spontaneous magnetic anisotropy induced by spin reorientation causes renewed interests in rare-earth orthochromites [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. The compounds RCrO 3 (R ¼La-Lu, and Y) crystallize in orthorhombic distorted perovskite structure with four formula units per unit cell [27].…”

Large exchange bias effect in LaCr0.9Ru0.1O3

“…These observations suggest that the mixed magnetic phase can be introduced by proper doping either at R site or Cr site. A few pure RCrO 3 (R¼Nd and Sm) exhibit EB effect [13,14]. An exchange bias effect below 200 K is observed for Pr doped LCO [8].…”

Origin of the magnetization and compensation temperature in rare-earth orthoferrites and orthochromates

“…Further, the coupling in Eq. (2) renders a picture in which the magnetic ordering of the M spins and the oxygen octahedral tilting work together to create an effective magnetic field, B R eff , acting on the rare-earth sublattice and given by 31,33,35 ) the net magnetization vanishes at a specific compensation temperature, T comp . This effect has been attributed to the fact that, below a certain temperature, the R ions acquire a magnetization that is opposite to that of the Fe/Cr sublattice and grows faster than the one of the B ions when further decreasing the temperature, 26,27 as suggested by the relatively large paramagnetic susceptibility of the R spins.…”