Electronic phase transitions and magnetoresistance in a new bilayer manganate, Ca_2.5Sr_0.5GaMn₂O₈

Abstract

The crystal structure of the anion-deficient perovskite Ca2.5Sr0.5GaMn2O8 has been studied at 290 and 5 K by neutron diffraction (290 K; space group Pcm21, a = 5.4294(1), b = 11.3722(3), c = 5.2983(1)Å). The vacant oxide sites order to create a structure in which perovskite bilayers consisting of MnO6 octahedra are isolated from each other along [010] by a single layer of GaO4 tetrahedra. At 5 K the material is antiferromagnetic with an ordered magnetic moment of 3.09(1) μB per Mn cation. Magnetic susceptibility measurements suggest that short-range magnetic ordering within the bilayers occurs above 200 K, and muon spin relaxation data show that the transition to long-range magnetic order occurs between 150 and 125 K. The resistivity of Ca2.5Sr0.5GaMn2O8 decreases by an order of magnitude at 125 K, and ∼50% magnetoresistance is seen in a field of 80 kOe at 110 K.

Ferromagnetic clusters in the Brownmillerite bilayered compounds Ca2.5−xLaxSr0.5GaMn2O8: An approach to achieve layered spintronics materials

“…16 Further neutron diffraction study confirmed the presence of an AFM short-range spin-spin correlation.…”

“…16 The magnetic properties of the iso-structural compound Ca 2.5 Sr 0.5 GaMn 2 O 8 show a 3D short-range antiferromagnetic (AFM) ordering above 170 K, a 2D long-range AFM ordering over 160-170 K, and then a 3D long-range AFM ordering below ~ 150 K 18 with an ordered magnetic moment of 3.09 (1) μ B per Mn cation at 5 K (aligned along…”

“…However, this system shows an AFM-insulating behavior. 16 Now, if one can make the magnetic layers (MnO 6 bilayers) as a ferromagnetic (FM)-metallic in nature, the resulting compound becomes a system with a natural array of the FM-metallic (MnO 6 bilayer) / non- Significantly, the present study shows that the magnetic and electronic properties of the layered system Ca 2.5 Sr 0.5 GaMn 2 O 8 can be tuned/optimized by appropriate chemical substitution to achieve new spintronic material based on naturally occurring layered system for practical applications. The powder x-ray diffraction (XRD) measurements were performed on the samples at The temperature dependent resistivity measurements were performed using the standard four-probe method in the temperature range ~100-320 K under zero applied magnetic field.…”

“…The temperature dependence of resistivity indicates that the samples are insulating in nature. Battle et al 16 reported a drop in the resistivity value by an order of magnitude at ~125…”

An Ising ferrimagnet with layered and chained magnetic sublattices:

“…The site asymmetry Z ¼ ðV xx À V yy Þ=V zz is large, sensing rather ''pseudotetrahedral'' than tetrahedral point-charge geometry. site in manganite Ca 2:5 Sr 0:5 GaMn 2 O 8 gives birth to the n ¼ 2 brownmillerite phase, with the sequence of octahedral and tetrahedral layers OOTOOT [22]. Furthermore, it was shown recently in this brownmillerite-derived family that there exist also the n ¼ 3 member Ca 2 MnAlO 5:5 with the layered pattern OOOTOOOT 0 and the structure period as large as 2.9533 nm [23].…”