Influence of pressure on the magnetic behavior and the anomalous magnetoresistance inTb5Si3

Abstract

The compound, Tb 5 Si 3 , crystallizing in Mn 5 Si 3 -type hexagonal structure, was recently reported by us to exhibit a sudden and huge enhancement in electrical resistivity (ρ) at a critical magnetic field (H cr ) in the magnetically ordered state (< 70 K) tracking isothermal magnetization (M) behavior. We have investigated the influence of external pressure (≤15 kbar) and negative chemical pressure induced by Ge substitution for Si on M and ρ as a function of temperature (5-300 K) and magnetic field (<120 kOe), with the primary aim of understanding the field-induced anomalies. Focusing on isothermal M and magnetoresistance (MR) at two temperatures, 5 and 20 K, we find that this ρ anomaly persists under external as well as negative chemical pressures, however, with a change in the H cr . The pressure-derivative of H cr is negative and this trend and the MR behavior at the H cr are comparable to that observed in some Laves phase itinerant magnetic systems. On the basis of this observation, we speculate that the magnetic fluctuations induced at this critical field could be responsible for the MR anomalies. INTRODUCTION The process of metamagnetism [1], in which a low magnetic moment state of a magnetic material gets transformed to a high magnetic moment state with the application of an external magnetic field (H ext ), continues to attract attention in condensed matter physics. Some phenomena like 'giant magnetoresistance' and the 'giant magnetocaloric effect', which are of great current interest, are closely associated with this process. In particular, for the case of rareearth (R) intermetallics, such a field-induced change in magnetism has been widely reported in the literature. In these local-moment systems, the electrical resistivity (ρ) at the metamagnetic transition usually decreases resulting in negative magnetoresistance, MR [defined as {ρ(H)-ρ(0)}/ρ(0)], due to a reduction in magnetic scattering by the application of magnetic field (H). The reader may see, for instance, Ref. 2 for the behavior of the MR in Gd 5 Si 2 Ge 2 and in DySb following the metamagnetic transition. In contrast to this general behavior, recently we observed [3] an enhanced positive MR at the field-induced magnetic transition in the case of a localmoment system, Tb 5 Si 3 . We considered it important to obtain more experimental results on this compound to understand the origin of such a MR anomaly.At this juncture, it is to be noted that the itinerant systems [4] exhibiting the field-induced magnetic anomalies gained considerable theoretical and experimental interest. In particular, the above mentioned MR anomaly was in fact observed in the cubic Laves phase family, RCo 2 . These binary compounds have been subjected to intense experimental investigations over a period of two decades [5][6][7][8][9]. In these systems, the existence of field-induced transitions and MR anomalies is known to originate from the existence of a peak in the Co 3d density of states in the vicinity of Fermi level. Yamada [7] theoretically predicted that the ...

Solidification and crystal growth of binary Tb5Si3 intermetallics

“…It was accompanied by a curious behavior with a positive magnetoresistance following the metamagnetic transition. An unusual sensitivity of the electrical resistivity to a small magnetic field under pressure [10] and an influence of pressure on the magnetic behavior have also been detected [11]. Tb 5 Si 3 single crystals are highly desirable for revealing this curious physical behavior and its dependence on crystallographic orientation and on the direction of the applied external field.…”

Magnetic anomalies in single crystalline Tb5Si3

“…The Tb 5 Si 3 single crystals of 6mm in diameter and 30 mm length were grown at 3mm/h zone travelling velocity. The crystals were characterized by x-ray diffraction and the lattice constants were found to be a= 8 Measurement System (Quantum Design) in the transverse mode. The data were collected after cooling the sample from 120 K to the desired temperature in zero magnetic field.…”

“…This emphasizes that there could be a subtle difference in the physical origin of these transitions, for example, 'inverse metamagnetism' [3,4,[8][9][10] near 55 kOe and well-known metamagnetism near 75 kOe for 5 K. Otherwise, other features (increase of MR in the reverse cycle with a peak and hysteretic effect) are qualitatively the same as that observed for polycrystalline samples and the readers may see earlier publications [3,[8][9][10][11][12] for the implications (e.g., unusual nature of magnetic phase co-existence phenomenon in some field-range while reversing the field, involving high-resistive high-field phase and low-resistive low-field phase). It is also to be noted that the value of MR at the peak of the curves is several hundred percent, much larger than that observed for polycrystals.…”

“…In the magnetically ordered state, there is a field-induced magnetic transition and H c increases with decreasing temperature in the forward leg of magnetic-field cycle, attaining a value of about 58 kOe at 1.8 K and there is a positive jump in MR at H c [3,[8][9][10][11][12]. A careful look at our results revealed that there could be more than one magnetic anomaly in the vicinity of 69 K in agreement with earlier literature [13] and that there could be additional steps in isothermal magnetization (M).…”

Особенности электронной структуры и спектральных характеристик соединения Gd-=SUB=-5-=/SUB=-Si-=SUB=-3-=/SUB=-

“…В результате конкуренции таких взаимодействий происходит формирование раз-личных типов неколлинеарных магнитных структур, существенно влияющих на магнитные и транспортные характеристики соединений R 5 Si 3 . Установлено, что эти характеристики проявляют аномальное поведение под влиянием внешних воздействий [10][11][12][13][14][15][16]. Разнообразие физических свойств указанных интерметаллидов стиму-лирует интерес к исследованию их электронной структу-ры.…”