Tailoring the magnetism of Tb5Si2Ge2compounds by La substitution

Abstract

In order to study the crystal structure, phase relationships, and magnetic properties of the system Tb 5−x La x Si 2 Ge 2 , a series of polycrystalline samples with compositions ranging from x = 0 to x = 5 have been synthesized and characterized in detail. At room temperature, two structures have been detected: Compounds in the concentration range 0 x < 1 present a monoclinic Gd 5 Si 2 Ge 2 -type structure, while for x > 1 a tetragonal Zr 5 Si 4 -type structure is observed. The unit cell volume increases linearly with La concentration but with two different slopes: ∼18Å3 /x and ∼33Å 3 /x for 0 x < 1 (monoclinic) and x > 1 (tetragonal), respectively. In the monoclinic region, an increase of T C was observed, reaching a maximum value of T C ∼ 154 K, at the x = 0.75 composition. This feature is explained based on specific La occupancy at the R2 site which was supported by density functional calculations for low La concentration. The samples that crystallized in the tetragonal structure exhibit a linear decrease of T C (x) with a slope of ∂T C /∂x ∼ −38 K/x, reaching 0 K for the x = 5 composition. A magnetic and structural x-T phase diagram of the Tb 5−x La x Si 2 Ge 2 system in the temperature range 4-300 K is proposed.

Phase Competitions behind the Giant Magnetic Entropy Variation: Gd5Si2Ge2 and Tb5Si2Ge2 Case Studies

“…Such phenomenon was firstly reported in the Tb 5 Si 2 Ge 2 compound, when it was associated with the experimentally observed deviation from the expected linearity (from Curie-Weiss law) of the 1   (T) curve in the paramagnetic region, T > T C [33]. Later, different works, reported by Ouyang, Tian, Pereira and co-workers identified the Griffiths-like phase in other compounds of the R 5 T 4 family [23,[48][49][50]. All these compounds presented anomalies featuring their reciprocal susceptibility curve: a "stair-like" behavior occurring in an intermediate temperature region, T C < T < T G .…”

“…The remaining relevant information is summarized in Table 1. 95 [29] 270 [30,31] Although these compounds were already thoroughly studied [8,23,32,33], in order to exemplify the broad range of application of this procedure, we will only take into account the fact that both materials undergo structural transitions under temperature and/or magnetic field changes. We will also assume that for both structures involved, the FM state is the most stable at low temperatures. ]…”

“…In systems exhibiting magnetostructural transitions there is a strong competition between the magnetic and crystallographic degrees of freedom involved in the transition, which is very sensitive to extrinsic parameters-such as temperature, magnetic field, pressure-and intrinsic properties-disorder (chemical and strain) and microstructure [1,[21][22][23][24]. It is very difficult to theoretically predict the influence of intrinsic properties, but the effect of external parameters, such as magnetic field and temperature, can be predicted.…”

Suppression of magnetostructural transition on GdSiGe thin film after thermal cyclings

“…They transform from a magnetically disordered state to an ordered state (at a temperature close to its critical temperature), and consequently large magnetic entropy changes occur. In recent years, techniques such as doping and thermal treatments have been used to enhance the magnetocaloric effect [5][6][7][8][9][10][11] . It is consensual that the magnetic materials undergoing first-order phase transitions are the ones exhibiting larger MCE, which is a key-parameter for their application in refrigeration systems.…”

On the Growth and Physical-chemical Characterization of Tb5Si2Ge2 Thin Films Produced by Electron-beam Evaporation

“…In contrast, Tb 5 Si 2 Ge 2 undergoes first the structural and then the magnetic transition, at 95 K and 112 K, respectively on heating [17,18]. Nevertheless, the ability of coupling the magnetic and structural transition lead to a GMCE, as observed previously by applying external pressure or by Fe alloying [19,20]. The first thin film on this family of materials was produced by Hadimani and co-authors on Gd 5 Si 2.09 Ge 1.91 using femtosecond pulsed laser deposition, only presenting a magnetic transition [12], to the best of our knowledge, there are no reports on the successful deposition of Tb 5 Si 2 Ge 2 thin films, which show relevant physical properties for applications, namely high magnetic anisotropy like in case of Tb-Si thin film [21].…”