Magnetic Properties of Sm 0.7 Ho 0.3 Fe 3 (BO 3 ) 4
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DISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Magnetic Properties of Sm0.7Ho0.3Fe3(BO3)4 A. A. Demidova,*, I. A. Gudimb, and E. V. Ereminb a
Bryansk State Technical University, Bryansk, 241035 Russia *email: [email protected] bKirensky Institute of Physics, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, 660038 Russia Received March 14, 2012
Abstract—The magnetic properties of a ferroborate single crystal of substituted composition Sm0.7H0.3Fe3(BO3)4 with competing Sm–Fe and Ho–Fe exchange interactions are studied. The measured properties and effects are interpreted in terms of a general theoretical approach based on the molecular field approximation and calculations using the crystal field model for a rareearth ion. The experimental temper ature dependences of the initial magnetic susceptibility in the temperature range 2–300 K, the anomalies in the magnetization curves for B || c and B ⊥ c in fields lower than 1.2 T, and the field and temperature depen dences of magnetization in fields lower than 9 T are described. The crystal field parameters and the parame ters of the R–Fe and Fe–Fe exchange interactions are determined during the interpretation of the experi mental data. DOI: 10.1134/S1063776112100020
INTRODUCTION Trigonal rareearth ferroborates RFe3(BO3)4 (R = Y, La–Lu) are of particular interest for the physics of magnetic phenomena as f–d compounds with a spe cific interaction of their rareearth and iron sub systems. Modern intense interest in the ferroborates is caused by the multiferroelectrical properties detected in them [1–3]. Since the discovery of new ferroborates of substituted compositions R1 – x R 'x Fe3(BO3)4, new possibilities for composition variations appeared and resulted in a variety of physical properties [4–9]. The iron subsystem in ferroborates becomes ordered at Néel temperatures TN ~ 30–40 K. Their rareearth subsystem is magnetized by an f–d interac tion and makes a significant contribution to magnetic anisotropy and the orientation of magnetic moments. Ferroborates can be easyaxis (magnetic moments of R = Pr, Tb, Dy, Fe are oriented along the c axis of a crystal) or easyplane (magnetic moments of R = Y, Nd, Sm, Eu, Er, Fe lie in the ab plane of a crystal) compounds or can pass spontaneously from the easy axis to the easyplane state, as in GdFe3(BO3)4 and HoFe3(BO3)4 (see, e.g., review [3]). The belonging of the ferroborates of substituted composition R1 – x R 'x Fe3(BO3)4 to the class of multi ferroics is being established [4, 6–8], and the effects caused by the competition of contributions, e.g., spontaneous reorientation transitions between the easyaxis and easyplane states, can appear if compet ing R–Fe and R'–Fe exchange interactions are present in them [4–8]. The available spectroscopic [10], magnetic, mag netoelectric, and magnetoelastic [3, 11–13] informa
tion indicates that the magnetic moments of iron in SmFe3(BO3)4 are antiferromagnetically ordered at TN ≈ 32–33 K and lie in the ab basal plane. Moreover, the magnetic moments of samariu
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