J Supercond Nov Magn (2016) 29:15–18 DOI 10.1007/s10948-015-3283-3 LETTER Non-resonant Microwave Absorption in Terbium Powders G. Alvarez 1,2 · H. Montiel 3 · A. Conde-Gallardo 2 · R. Zamorano 1 Received: 10 November 2015 / Accepted: 14 November 2015 / Published online: 25 November 2015 © Springer Science+Business Media New York 2015 Abstract The non-resonant microwave absorption is reported in terbium powders at X-band (8.8–9.8 GHz) in the 160–300 K temperature region. Two microwave absorption-type responses are observed as follows: the mag- netically modulated microwave absorption spectroscopy (MAMMAS) and the low-field microwave absorption (LFMA). MAMMAS response detects the paramagnetic to antiferromagnetic-helical and to ferromagnetic transition at T N = 227 K and T C = 214 K, respectively, being con- firmed by means of magnetic measurements. Additionally, LFMA response is only observed at temperatures below ∼230 K, and it is associated with the magnetic order (antiferromagnetic-helical/ferromagnetic) at low tempera- ture in terbium powders. Keywords Terbium powders · Non-resonant microwave absorption · Magnetic transitions  G. Alvarez memodin@yahoo.com 1 Escuela Superior de F´ ısica y Matem´ aticas del Instituto Polit´ ecnico Nacional, U.P.A.L.M, Edificio 9, Av. Instituto Polit´ ecnico Nacional S/N, San Pedro Zacatenco, M´ exico DF 07738, M´ exico 2 Departamento de F´ ısica, CINVESTAV-IPN, A.P. 14-740, M´ exico DF 07360, M´ exico 3 Centro de Ciencias Aplicadas y Desarrollo Tecnol´ ogico de la Universidad Nacional Aut´ onoma de M´ exico, Cd. Universitaria, A.P. 70-186, M´ exico DF 04510, M´ exico 1 Introduction The heavy rare-earth metals have a hexagonal close-packed structure, and the magnetically ordered phases of the 4f -moments found in these metals are either ferromag- netic or the moments are antiferromagnetically modulated along the c-axis. In this latter magnetic-type order, the individual hexagonal layers are uniformly magnetized in a direction that changes from one layer to the next and the basic arrangements of the magnetic moments were deter- mined by neutron-diffraction experiments by Koehler in the 1960s [1]. In particular, the terbium is an easy-planar magnet in which the magnetic moments are ordered in an antiferromagnetic-helical structure at T N = 230 K, and it becomes a basal-plane ferromagnet with a phase transition at T C ∼220 K [1, 2]. On the other hand, the non-resonant microwave absorp- tion (NRMA) has been mainly employed to study at superconductor materials [3–7]. NRMA response is usually detected as a function of temperature (at a constant dc field) or as a function of an applied dc magnetic field (at con- stant temperature), being historically denominated as fol- lows: magnetically modulated microwave absorption spec- troscopy (MAMMAS) [4, 6–8] and low-field microwave absorption (LFMA) [3, 5–7], respectively. It is also nec- essary to mention that NRMA response may be caused not only by the superconductivity but also by phenomena associated with magnetic field-dependent microwave losses in the materials [7–9]. MAMMAS technique can be well adapted to detect a wide range of magnetic transitions in materials [7–9], where this microwave absorption profile can provide valuable information about the nature of the magnetic ordering and the different dissipative dynamics