Broadband transverse susceptibility in multiferroic Y-type hexaferrite Ba0.5Sr1.5Co2Fe2O22

Abstract

Single phase multiferroics in which ordered magnetism and ferroelectricity coexist, are of great interest for new multifunctional devices, and among them Y-type hexaferrites are good candidates. Transverse susceptibility measurements, which have been proved to be a versatile tool to study singular properties of bulk and nanoparticle magnetic systems, have been carried out with a broadband system on polycrystalline Y type hexaferrites with composition Ba 0.5 Sr 1.5 Co 2 Fe 2 O 22 , optimal to exhibit multiferroic properties. In the temperature range 80-350 K transverse susceptibility measurements with DC fields up to ±5000 Oe reveal different behaviour depending on the sintering temperature. The thermal evolution of the anisotropy field peak exhibits four regions with different slopes: positive in 80-130 K, negative in 130-200 K, constant in 200-280 K and negative in 280-350 K, which can be considered a signature of spin transitions in this compound.

Broadband transverse susceptibility in multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22

“…The diffraction patterns reveal that samples sintered at 1050 ºC and 1150 ºC (samples A and B) are single phase Y-type hexaferrites with space group R-3m [11]. Sample C corresponds to Y type hexaferrite with secondary phase of Z type, together with SrFe 2 O 4 , so that the sintering temperature effect on phase formation is very similar to the observed in previous works [29]. The lattice parameters and particle sizes obtained for these samples reveal minor changes in the Y-type phase with the increase in sintering temperature: a= 5.8689 Ǻ, and c= 43.4760 Ǻ for the sample A, and 5.8634 Ǻ, and 43.4468 Ǻ for the sample B, whereas crystallite sizes are both around 100 nm (from Scherrer formula) and particle sizes of 2-6 m (from TEM results, not shown) in good agreement with literature data [13,31,32].…”

“…However, we can see clear differences among the sample sintered at 1250 ºC and the others. In the former we can observe that at low measuring temperatures the amplitude of TS is small and increases strongly over room temperature, being this behaviour similar to the Y-type system prepared with Co [29]. On the contrary, the latter exhibit a wide region at low temperatures with TS amplitude close to the maximum, a sudden decrease around room temperature, and a further increase to a lower TS peak around 7 % to finally reduce to zero when the temperature goes over the Nèel temperature.…”

“…In this sample the peak related to anisotropy at low T meas shifts slightly to higher applied fields, from 300 Oe at T meas =80 K to 400 Oe at T meas =220 K, and then reduces to zero at the top measuring temperature tested. This behaviour is to some extent similar to that observed in CoY hexaferrites [29], unless the comparative analysis of these two systems will be postponed to a further paper.…”

“…Transverse susceptibility measurements were carried out with a broadband automatic system [29] in which the sample rods form the core of a coil that produces a longitudinal AC magnetic field with frequency 1 kHz and maximum amplitude of 2 Oe. The sampleholder with the coil and a heating element is put inside a cryostat to allow temperature measurements in the range 80 K-350 K. The cryostat tail lies into the polar pieces of an electromagnet fed by a power supply Agilent 6675A that produces a DC magnetic field, measured with a FW Bell 5080 gaussmeter, perpendicular to the AC magnetic field.…”

“…Despite the early description of this kind of measurement [26] and its application [23], it is still of interest in nanoparticle magnetic systems [27,28]. In this work TS measurements have been carried out with a broadband system based on a LCR meter [29] on Y type hexaferrites with composition Ba 0.5 Sr 1.5 Zn 2 Fe 12 O 22 , (BSZFO) optimal to exhibit multiferroic properties [14]. According with our previous experience we expect that the different spiral magnetic configurations alter the TS results.…”