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Magnetic properties of solid solutions between BiCrO 3 and BiGaO 3 with perovskite structures

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ABSTRACT

Magnetic properties of BiCr1−xGaxO3 perovskite-type solid solutions are reported, and a magnetic phase diagram is established. As-synthesized BiCrO3 and BiCr0.9Ga0.1O3 crystallize in a monoclinic (m) C2/c structure. The Néel temperature (TN) decreases from 111 K in BiCrO3 to 98 K in BiCr0.9Ga0.1O3, and spin-reorientation transition temperature increases from 72 K in BiCrO3 to 83 K in BiCr0.9Ga0.1O3. o-BiCr0.9Ga0.1O3 with a PbZrO3-type orthorhombic structure is obtained by heating m-BiCr0.9Ga0.1O3 up to 573 K in air; it shows similar magnetic properties with those of m-BiCr0.9Ga0.1O3. TN of BiCr0.8Ga0.2O3 is 81 K, and TN of BiCr0.7Ga0.3O3 is 63 K. Samples with x = 0.4, 0.5, 0.6 and 0.7 crystallize in a polar R3c structure. Long-range antiferromagnetic order with weak ferromagnetism is observed below TN = 56 K in BiCr0.6Ga0.4O3, TN = 36 K in BiCr0.5Ga0.5O3 and TN = 18 K in BiCr0.4Ga0.6O3. BiCr0.3Ga0.7O3 shows a paramagnetic behaviour because the Cr concentration is below the percolation threshold of 31%.

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Real parts of the ac susceptibility curves of BiCr1−xGaxO3 (x = 0 [17] and m—0.1). TN is the Néel temperature, and TSR is temperature of a spin-reorientation transition. The data for m-BiCr0.9Ga0.1O3 are shifted by +0.01 cm3/mol-Cr for the clarity.
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Figure 5: Real parts of the ac susceptibility curves of BiCr1−xGaxO3 (x = 0 [17] and m—0.1). TN is the Néel temperature, and TSR is temperature of a spin-reorientation transition. The data for m-BiCr0.9Ga0.1O3 are shifted by +0.01 cm3/mol-Cr for the clarity.

Mentions: BiCrO3 has the Néel temperature (TN) of 111 K (determined/defined here by peak positions on the FC dχ/dT versus T curves at 100 Oe). Below TN, the magnetic moments of Cr3+ ions in BiCrO3 are aligned along the a axis [14] in the G-type antiferromagnetic (AFM) structure, where all Cr–O–Cr interactions are AFM. BiCrO3 has a spin-reorientation transition (TSR) at 72 K (also defined by peak positions on the FC dχ/dT versus T curves at 100 Oe), where Cr3+ spins start to rotate away from the a axis in the (a, c) plane [13], but keeping the G-type AFM arrangement. Characteristic anomalies at TN and TSR can be clearly seen on the χ versus T, dχ/dT versus T and χ′ versus T curves of BiCrO3 and m-BiCr0.9Ga0.1O3 (figures 4(a), (b) and 5). We note that small anomalies are observed at 165 K in BiCrO3 on the 100 Oe FC χ−1 versus T curve (figure 4(c)); they were suggested to originate from a very small amount of the GdFeO3-type Pnma modification of BiCrO3 [4, 18]. We note that those anomalies at 165 K with different magnitudes were observed in all checked BiCrO3 samples (about a dozen of different samples (figure S17 of ESI), even synthesized by different groups); and those anomalies cannot be eliminated by further annealing and very slow cooling [18] suggesting that they are ‘intrinsic’ for bulk BiCrO3 samples. As-synthesized m-BiCr0.9Ga0.1O3 shows very similar magnetic behaviour with that of BiCrO3, but with TN = 98 K and TSR = 83 K. No additional magnetic anomalies above TN are found in m-BiCr0.9Ga0.1O3 in comparison with BiCrO3; it can be related with the higher temperature of the C2/c-to-Pnma transition in BiCr0.9Ga0.1O3 that results in a complete transformation. Magnetic properties of m-BiCr0.9Ga0.1O3 and o-BiCr0.9Ga0.1O3 are very similar with each other (figures 4 and S13 of ESI). Inverse magnetic susceptibilities of BiCrO3, m-BiCr0.9Ga0.1O3 and o-BiCr0.9Ga0.1O3 are given on figure 4(c). They show a noticeable deviation from the Curie–Weiss behaviour far above TN; this is why the Curie–Weiss fits are performed above 250 K for those samples (table 1). This fact can also explain why the effective magnetic moments are slightly larger than expected ones.


Magnetic properties of solid solutions between BiCrO 3 and BiGaO 3 with perovskite structures
Real parts of the ac susceptibility curves of BiCr1−xGaxO3 (x = 0 [17] and m—0.1). TN is the Néel temperature, and TSR is temperature of a spin-reorientation transition. The data for m-BiCr0.9Ga0.1O3 are shifted by +0.01 cm3/mol-Cr for the clarity.
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Figure 5: Real parts of the ac susceptibility curves of BiCr1−xGaxO3 (x = 0 [17] and m—0.1). TN is the Néel temperature, and TSR is temperature of a spin-reorientation transition. The data for m-BiCr0.9Ga0.1O3 are shifted by +0.01 cm3/mol-Cr for the clarity.
Mentions: BiCrO3 has the Néel temperature (TN) of 111 K (determined/defined here by peak positions on the FC dχ/dT versus T curves at 100 Oe). Below TN, the magnetic moments of Cr3+ ions in BiCrO3 are aligned along the a axis [14] in the G-type antiferromagnetic (AFM) structure, where all Cr–O–Cr interactions are AFM. BiCrO3 has a spin-reorientation transition (TSR) at 72 K (also defined by peak positions on the FC dχ/dT versus T curves at 100 Oe), where Cr3+ spins start to rotate away from the a axis in the (a, c) plane [13], but keeping the G-type AFM arrangement. Characteristic anomalies at TN and TSR can be clearly seen on the χ versus T, dχ/dT versus T and χ′ versus T curves of BiCrO3 and m-BiCr0.9Ga0.1O3 (figures 4(a), (b) and 5). We note that small anomalies are observed at 165 K in BiCrO3 on the 100 Oe FC χ−1 versus T curve (figure 4(c)); they were suggested to originate from a very small amount of the GdFeO3-type Pnma modification of BiCrO3 [4, 18]. We note that those anomalies at 165 K with different magnitudes were observed in all checked BiCrO3 samples (about a dozen of different samples (figure S17 of ESI), even synthesized by different groups); and those anomalies cannot be eliminated by further annealing and very slow cooling [18] suggesting that they are ‘intrinsic’ for bulk BiCrO3 samples. As-synthesized m-BiCr0.9Ga0.1O3 shows very similar magnetic behaviour with that of BiCrO3, but with TN = 98 K and TSR = 83 K. No additional magnetic anomalies above TN are found in m-BiCr0.9Ga0.1O3 in comparison with BiCrO3; it can be related with the higher temperature of the C2/c-to-Pnma transition in BiCr0.9Ga0.1O3 that results in a complete transformation. Magnetic properties of m-BiCr0.9Ga0.1O3 and o-BiCr0.9Ga0.1O3 are very similar with each other (figures 4 and S13 of ESI). Inverse magnetic susceptibilities of BiCrO3, m-BiCr0.9Ga0.1O3 and o-BiCr0.9Ga0.1O3 are given on figure 4(c). They show a noticeable deviation from the Curie–Weiss behaviour far above TN; this is why the Curie–Weiss fits are performed above 250 K for those samples (table 1). This fact can also explain why the effective magnetic moments are slightly larger than expected ones.

View Article: PubMed Central - PubMed

ABSTRACT

Magnetic properties of BiCr1−xGaxO3 perovskite-type solid solutions are reported, and a magnetic phase diagram is established. As-synthesized BiCrO3 and BiCr0.9Ga0.1O3 crystallize in a monoclinic (m) C2/c structure. The Néel temperature (TN) decreases from 111 K in BiCrO3 to 98 K in BiCr0.9Ga0.1O3, and spin-reorientation transition temperature increases from 72 K in BiCrO3 to 83 K in BiCr0.9Ga0.1O3. o-BiCr0.9Ga0.1O3 with a PbZrO3-type orthorhombic structure is obtained by heating m-BiCr0.9Ga0.1O3 up to 573 K in air; it shows similar magnetic properties with those of m-BiCr0.9Ga0.1O3. TN of BiCr0.8Ga0.2O3 is 81 K, and TN of BiCr0.7Ga0.3O3 is 63 K. Samples with x = 0.4, 0.5, 0.6 and 0.7 crystallize in a polar R3c structure. Long-range antiferromagnetic order with weak ferromagnetism is observed below TN = 56 K in BiCr0.6Ga0.4O3, TN = 36 K in BiCr0.5Ga0.5O3 and TN = 18 K in BiCr0.4Ga0.6O3. BiCr0.3Ga0.7O3 shows a paramagnetic behaviour because the Cr concentration is below the percolation threshold of 31%.

No MeSH data available.