Hydrostatic pressure study of the paramagnetic-ferromagnetic phase transition in (Ga,Mn)As

Abstract

The effect of hydrostatic pressure on the paramagnetic -ferromagnetic phase transition has been studied in (Ga,Mn)As. The variation of the Curie temperature (T C ) with pressure was monitored by two transport methods: (1) -measurement of zero field resistivity versus temperature ρ(T), (2) -dependence on temperature of the Hall voltage hysteresis loop. Two specimens of different resistivity characteristics were examined. The measured pressure-induced changes of T C were relatively small (of the order of 1K/GPa) for both samples, however they were opposite for the two.(Ga,Mn)As is one of the most intensively investigated diluted magnetic semiconductors during last decades. The understanding of physical phenomena governing its magnetic properties is crucial for increasing Curie temperature (T C ) and thus for possible application of this material in spintronic devices. The origin of ferromagnetism in (Ga,Mn)As was quantitatively explained within the p-d Zener model assuming magnetic interaction between the localized magnetic moments of Mn 2+ ions mediated by holes in the valence band [1][2][3] . This model, in the case of semiconductors, where the carrier density is smaller than the magnetic ion concentration is equivalent to the Ruderman-Kittel-Kasuya-Yosida (RKKY) approach employed in the diluted magnetic metals 4 . Within this picture the ferromagnetic ordering temperature, T C depends in particular on the local p-d exchange interaction and a free hole concentration. It was demonstrated that indeed an increase of the hole concentration in a field effect transistor structure led to an enhancement of the ferromagnetic state 5. On the other hand it was found that the exchange energy scales with the lattice constant as, N 0 β ~ a 0 -3 , 1 and therefore an external hydrostatic pressure could influence the exchange coupling. Although the studies of (In,Mn)Sb diluted magnetic semiconductor under hydrostatic pressure provided an evidence for an increase in carrier-mediated magnetic coupling 6,7 , giving rise to higher Curie temperature, the effect of hydrostatic pressure on (Ga,Mn)As semiconductor is not as clear.6 Therefore additional study was performed in order to clarify the role of external hydrostatic pressure in the paramagneticferromagnetic phase transition in (Ga,Mn)As. p-type Ga 1-x Mn x As layers were grown by molecular beam epitaxy (MBE) on (100) GaAs substrate. In our studies two different samples were used: A777 and A963. The former sample had 20 nm thick layer of (Ga,Mn)As with Mn content x = 7%. After the MBE growth this sample was capped with amorphous As and annealed in the MBE growth chamber at the temperature of 210 ºC (controlled by the IR pyrometer) for two hours (see Ref. 8 for details). The Curie temperature determined from SQUID magnetometry was close to 85 K (Fig. 1, open symbols). The latter sample had a (Ga,Mn)As layer of 50 nm and x = 6%. This sample was not annealed after the MBE growth. The Curie temperature for A963 sample was approximately 50 K (Fig. 1, solid symbols). Since the amount o...

(Ga,Mn)As under pressure: A first-principles investigation

“…The first is a narrowgap topological insulator (Sb,V) 2 Te 3 [9], in which rather than intraband excitations (i.e., the standard RudermanKittel-Kasuya-Yosida mechanism), interband excitations (i.e., the Bloembergen-Rowland interactions) give a dominant contribution to the coupling between localized spins of transition metals (TMs) [6]. The second is (Ga,Mn)As in the vicinity of the metal-insulator transition, where the increase in the p-d hybridization enhances hole localization and, hence, diminishes T C [10].…”

“…There exists a number of experimental studies on the variation of T C under pressure for DMSs: (Pb,Sn,Mn)Te [7], (In,Mn)Sb [4,8], (Sb,V) 2 Te 3 [9], (Ga,Mn)As [8,10], and (Ge,Mn)Te [11]. The results of those studies reveal that for samples with high concentrations of band holes, T C increases with an increasing hydrostatic pressure p according to the expectations of the p-d Zener model [12].…”

Influence of Epitaxial Strain on Magnetic Anisotropy in (Ga,Mn)As

“…2). Shape of R XY (B) function shows that sample 2 exhibits an in-plane easy axis (compare with the hysteresis loops published in [5] for sample A963, which is the same sample). Anisotropy eld B A as a function of temperature was determined from experimental data using Eq.…”

“…Lattice mismatch calculated basing on Vegard's law [2] was equal to ε = −0.3% and ε = +0.6% for sample 1 and 2, respectively. Data for sample 2 was published in [5] as sample A963.…”

Emergence of pressure-induced metamagnetic-like state in Mn-doped CdGeAs2 chalcopyrite

“…In addition, the magnetovolume effect in Cd 1-x Mn x GeAs 2 reaches a value of spontaneous magnetostriction ω S =0.5-1.7% that significantly shifts the T C with dT C /dP ≈ -14.0 ÷ -6.8 K/GPa, which greatly exceeds the value of 2.7 K/GPa for Ge 1-x Mn x Te [16] and 1 K/GPa for (GaMn)As [17]. Thus, the ferromagnetic chalcopyrites demonstrate extreme sensitivity to external disturbances that motivates further interest to them via high-pressure studies.…”