Journal of Alloys and Compounds 375 (2004) 31–33 Magnetic and structural studies of GdFe 2-x Hf x alloys I.A. Al-Omari a,∗ , S. Aich b a Department of Physics, Sultan Qaboos University, P.O. Box 36, PC 123, Muscat, Oman b Department of Mechanical Engineering, University of Nebraska, Lincoln, NE 68588, USA Received 10 October 2003; received in revised form 19 November 2003; accepted 19 November 2003 Abstract A series of GdFe 2-x Hf x alloys, where x = 0, 0.1, 0.15, 0.2, and 0.3, have been prepared by arc-melting. X-ray diffraction (XRD) reveals that all the samples studied have the cubic Cu 2 Mg type structure. The lattice parameter (a) and the unit cell volume (V) are found to increase with increasing Hf concentration. The magnetization were measured in a superconducting quantum interference device magnetometer (SQUID) in the temperature range 5–300 K. All samples under investigation are magnetically ordered at room temperature and at 5 K and the saturation magnetization is found to increase with increasing the Hf concentration at both temperatures. The increase in the saturation magnetization is due to the replacement of magnetic Fe by non-magnetic Hf which reduces the Fe sublattice moment in the GdFe 2-x Hf x ferromagnetic alloys. The Curie temperature (T c ) is determined using vibrating sample magnetometer (VSM) for all samples and found to decrease linearly with increasing Hf concentration, from 800 K for x = 0–590 K for x = 0.3. © 2003 Elsevier B.V. All rights reserved. PACS: 75.50.Bb; 75.50ww; 75.60.E; 61.18.F Keywords: Lattice parameter; Saturation magnetization; Curie temperature; Rare earth compounds; Transition metal compounds; Magnetic measurements 1. Introduction The intermetallic GdFe 2 alloys have the cubic C15 struc- ture (Laves phase), where Gd and Fe are coupled ferrimag- neticaly. This system of alloys and other similar systems display a quite distinct behavior when Fe is replaced by non-magnetic elements. Such systems are often studied both experimentally and theoretically because of scientific and practical reasons. For instance, the increase in magnetic or- dering temperature or magnetic moments is an important practical task. Buschow [1,2] studied the Gd–Fe system and found that GdFe 2 has a magnetic ordering temperature, T c = 796 K, and a saturation moment of 3.55  B /f.u. In a study of the magnetic properties of the GdFe 2 H x ferrimagnet, Mush- nikov et al. [3] found that during hydrogenation there is a sharp decrease in the energy of the Gd–Fe exchange inter- action and an increase in the magnetic moment of iron from 1.6  B in the initial compound to 2.2  B in the amorphous hydride alloy. Other studies [4–7] of RFe 2 H x , where R = Ce, Er, and Ho, compounds for x up to 4.2 showed that the ∗ Corresponding author. Fax: +968-514228. E-mail address: ialomari@yahoo.com (I.A. Al-Omari). absorption of H causes the cubic structure to expand and af- fects strongly the strength of the exchange interaction in the ferromagnetic structure of HoFe 2 . A previous study by Tang [8] of Tb(Fe 1-x T x ) 2 com- pounds, where T = Ti, V, Cr, and Mn, reveals that the spontaneous magnetostriction changes slightly upon T sub- stitution for Fe due to the filling of the iron d-band. Duc et al. [9] studied Gd(Fe,Ti) 2 and found that the Curie tem- perature decreases with increasing Ti concentration from 820 K for GdFe 2 to 750 K for GdFe 1.8 Ti 0.2 while the ex- change parameter A Gd–Fe increases from 16.2 × 10 -23 J for GdFe 2 to 22.4 × 10 -23 J for GdFe 1.8 Ti 0.2 . Recently, Al-Omari et al. [10] studied the magnetic and structural properties of GdFe 2-x Ti x alloys and found that the satura- tion magnetization increases with increasing Ti concentra- tion from 0 to 0.3 at room temperature and at 5 K. The re- placement of 3d metal atoms by Al is a method often used to test the magnetic properties of compounds. The effect of Al substitution for Fe on that magnetic and structural properties of Gd(Fe 1-x Al x ) 2 alloys was studied by Steiner [11]. This study showed that the Curie temperature decreases with in- creasing aluminum concentration from 795 K for GdFe 2 to 540 K for Gd(Fe 0.8 Al 0.2 ) 2 , and it reaches 150 K for GdAl 2 . 0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2003.11.029