Topic Code:Invited
Magnetic field induced Elastic behaviour of FINEMET Melt spun ribbon
Md.Sarowar Hossain1, M.A. Hakim2 and P.K. Mukhopadhyay1*
1LCMP, S.N. Bose National Centre for Basic Sciences, Salt Lake, Kolkata-106, India
2DGCE, Faculty of Engineering, BUET, Bangladesh, Dhaka-1000, Bangladesh
1*
Abstract:Amorphous ribbons of the composition Fe76.5Cu1Si13.5B9(FINEMET)has been studiedbythe low temperature elastic properties using vibrating reed apparatus.Elastic properties were measured till 140K in presenceofand without magnetic field. Structural anomalies were found around 200K (ΔT = 4K) in zero field magnetic field which were shown as peaks in internal friction measurement and the same was replicated in the sound velocity. With the application of external field, the structural anomalies show a large thermal hysteresis,with width around 24K.
1. INTRODUCTION
FINEMET®materials are well known as Fe based alloys having nano crystalline grains, excellent soft magnetic properties and good stress sensing materials. While many studies have been carried out for soft magnetic properties of FINEMET, only a few workers have discussed magnetoelastic properties of FINEMET [1, 2]. The low temperature properties for the FINEMET samples is not reported so far. In the present workstudyof elastic properties through sound velocity and sound attenuation in low temperature (300K to 140K) has been carried out.
2. EXPERIMENTAL DETAILS
A Fe76.5Cu1Si13.5B9 metallic glass ribbon sample was prepared with the dimensions - 6 mm width and 20 to 22 µm thickness for our present study by melt spinning technique. Sample has been characterized by XRD, FE-SEM, VSM) from Lake Shore. The measurement of sound velocity and attenuation was done using vibration reed technique [3].A pair of externally mounted Helmholtz coils were used to generate of 300 Oe magnetic field.
2.1. Result and discussion
The XRD result and the FE-SEM image in Fig.2(a, b)confirm the amorphousity of the melt-spun ribbon.The magnetic moment in ZFC protocol for 50Oe applied field gradually increased and showed a small peak at around 340K and dropped till 400K. In 80K to 400K range sample showed ferromagnetic nature, as shown by quite high magnetic moment.
Fig.1(a) XRD and (b)of Fe76.5Cu1Si13.5B9
In Fig.2(a, b) we observed the relative change in sound velocity and internal friction(Q-1) as a function of temperature and hence shifting of transition temperature in presence of 300 Oe magnetic field.Itcanbe seen that as the temperature was lowered, initially the increased (meaning that the sample hardened) and the decreased (meaning that defects in the samples got pinned). However, at around 190K, both of these gave peaks signifying same structural changes occurring in the system. There is no magnetic transition around this temperature range, so the change must be due to structural change alone. But in presence of magnetic field of 300Oe the structural transition shifts to the lower side of temperature region (around 170K) with a larger thermal hysteresis. This is an unknown behavior and origin is unclear. We can only surmise that some structural reorganization must be taking place here, and the sample being ferromagnetic in nature, this was amplified in presence of external field.
Fig.2(a) sound velocity and (b)Q-1 under magnetic field and varying temperature
3. CONCLUSIONS
We found an amorphous FINEMETofsoft magnet with very low intrinsic coercivity. From the present sound velocity different structural anomalies were found at 180 K for the first time. We are yet to ascertain the reasons for it. However, on the whole the system showed good mechanical property.
4. ACKNOWLEDGMENT
SH is thankful to TWAS – Bose fellowship.
5. REFERENCE
[1] Pham DucThang, Hoang HaiDoung and Nguyen Hoang Nghi, J. Phys. 187, 1-5 (2009)
[2] L. Kraus and P. Švec J. Appl. Phys. Vol. 93, 7220 (2003)
[3]. P. K. Mukhopadhyay and A. K. Raychaudhuri, J. Phys. E. 20, 507 (1987)