Journal of Magnetism and Magnetic Materials 215}216 (2000) 355}358 Neutron irradiation e!ect on the magnetic properties in Fe  Zr  B  H.C. Kim, S.C. Yu*, C.G. Kim, H.S. Han, W.K. Cho Department of Physics, Chungbuk National University, Gaeshin-Dong San 48 Cheongju 361-763, South Korea Department of Physics, Sun Moon University, Chung-nam 336-840, South Korea HANARO Center, Korea Atomic Energy Research Institute, Taejon 305-600, South Korea Abstract The e!ects of neutron irradiation on the magnetic properties in Fe  Zr  B  (at%) amorphous ribbon were studied by hysteresis loop and complex permeability measurements. The #uxes of thermal (n  ) and fast neutrons (n  ) #uences were 3.0910n  cm s and 1.8710n  cm s, respectively. After neutron irradiation, the imaginary part of com- plex permeability in low-frequency region decreased due to the decrease of wall motion, but the permeability in high-frequency region increased due to the enhancement of rotational magnetization. As a whole, initial permeability in neutron irradiated sample was larger than that in as-quenched one, but the coercive force and saturation magnetization did not change signi"cantly after neutron irradiation.  2000 Elsevier Science B.V. All rights reserved. Keywords: Neutron irradiation; Complex permeability; Amorphous alloy 1. Introduction Several recent investigations have dealt with the in#u- ence of radiation e!ect on the magnetic properties of metallic glasses. The observed changes in various mag- netic parameters such as Curie temperature [1], mag- netic permeability [2] and hysteresis loop parameters [3] clearly demonstrate that metallic glasses can be struc- turally modi"ed by neutron irradiation. Also, it is already known that the change of magnetic properties of amorphous alloy after the neutron irradiation is mainly due to the internal stress at the induced defect, and relaxation frequency of permeability spectra has been discussed in terms of the induced stress [4]. The present study was undertaken in order to investi- gate the in#uence of neutron irradiation on magnetic properties of ferromagnetic Fe  Zr  B  amorphous rib- bon with the fast neutron #uences of 1.9210, 2.6310 and 4.8510n  cm. The hysteresis loop * Corresponding author. Tel.: #82-431-261-2269; fax:#82- 431-275-6416. E-mail address: scyu@cbucc.chungbuk.ac.kr (S.C. Yu). and magnetic permeability measurements were carried out with the aim of studying the change of soft magnetic properties from the domain wall motion and rotational magnetization before and after the neutron irradiation. 2. Experiment The amorphous Fe  Zr  B  ribbon was prepared by rapid quenching technique in vacuum. The ribbon sample was about 20 m thick and 2 mm wide. The amorphous state of the sample was con"rmed by the X-ray di!ractometer using Cu}K  H radiation. The sam- ples were irradiated for 72 h using HANARO research reactor at Korea Atomic Energy Research Institute, where the temperature of the samples during irradiation was monitored as about 473 K. The #uxes of thermal (n  ) and fast (n  ) neutrons were 3.0910n  cm s and 1.8710n  cm s, respectively. The total integ- rated fast neutron #uences were 1.9210, 2.6310 and 4.8510 n  cm. Thermal annealing of the amorphous state of the sample was also carried out for 72 h at the temperature of 473 K in order to estimate the thermal annealing e!ect. 0304-8853/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 1 5 7 - 8