57Fe NMR study of the magnetoelectric hexaferrite Ba0.5Sr1.5Zn

Abstract

Magnetoelectric hexaferrite Ba 0.5 Sr 1.5 Zn 2 Fe 12 O 22 (BSZFO) and Ba 0.5 Sr 1.5 Zn 2 (Fe 0.92 Al 0.08 ) 12 O 22 (BSZFAO) were investigated by 57 Fe nuclear magnetic resonance (NMR). The spin-canting angles of all NMR peaks were measured to assign each peak to corresponding Fe 3+ sites. It was revealed that the spin-canting angle of Fe 3+ ions at off-centered octahedra is fixed and Al 3+ ions substitute for Fe 3+ ions at those sites. The temperature dependence of the NMR frequency indicates that the low-temperature excitation is spin wave in ferromagnetic phase.

Effects of Al substitution and thermal annealing on magnetoelectric Ba0.5Sr1.5Zn2Fe12O22investigated by the enhancement factor of57Fe nuclear magnetic resonance

“…Then the data were taken during warming. The frequency of H 1 was 69 MHz, the frequency of the peak from tetrahedral and octahedral sites [14]. The shape and the frequency of the spectra are almost identical before and after annealing (figure 2(a)).…”

“…This conclusion, along with the fact that the slope of 1/T 2 changes around the CTC-ALC transition temperature, implies that the magnetic moments of the L and S blocks start to fluctuate as the temperature increases from zero, and that this increase becomes faster over 60 K. That is, the transition from CTC to ALC is gradual, not abrupt. Since the temperature dependence of the NMR frequency does not show any anomaly around 60 K [14], the fluctuation rate cannot be larger than the frequency at the point where the NMR spectrum was observed, at about 70 MHz.…”

“…Single crystals of BSZFO and BSZFAO were grown using the Na 2 O-Fe 2 O 3 flux method [13]; some of crystals were annealed under oxygen flowing condition at 900 °C for 8 days [11]. Annealed samples were the same samples used in [14]. 57 Fe NMR spectrum was obtained with our homemade spectroscopy using the standard Carr-Purcell spin-echo (π/2-π) sequence.…”

“…Fe 3+ ions are L = 0 ions but at the offcentered octahedra they have non-zero orbital moment, which is the origin of easy-plane magnetic anisotropy [7]. Since Al 3+ ions substitute for the Fe 3+ ions in the off-centered octahedral sites [14], the reduction of the easy-plane anisotropy seems to be natural. The as-grown BSZFAO needs larger H set than that of the annealed sample in order to develop the same net…”