Formation of short-range magnetic order and avoided ferromagnetic quantum criticality in pressurized LaCrGe3

Abstract

LaCrGe3 has attracted attention as a paradigm example of the avoidance of ferromagnetic (FM) quantum criticality in an itinerant magnet. Here, we combined thermodynamic (specific heat and thermal expansion), transport, x-ray, and neutron scattering as well as μSR measurements to obtain insights on the temperature-pressure phase diagram of LaCrGe3. Consistent with previous studies of the phase diagram by transport measurements, our thermodynamic data shows clearly that the FM transition at TFM changes its character from second order to first order when it is suppressed to low temperatures by pressure. In addition, previous studies demonstrated that for high pressures a new phase occurs below T2, which was proposed to be a long-wavelength antiferromagnetic state (AFMq). In this paper, we provide evidence from our thermodynamic data that this phase transition is preceded by yet another phase transition at T1>T2. Our μSR data indicate that full magnetic volume fraction is only established below T2, but that this magnetism is characterized by a short correlation length. Within the experimental resolution, our neutron-scattering data is not able to identify any magnetic Bragg peaks. Overall, the microscopic magnetic data is therefore consistent with the formation of FM clusters in the proximity of the avoided FM quantum critical point in LaCrGe3. This conclusion is at odds with the previous proposal of AFMq order and raises questions on the role of disorder in this stochiometric compound.

Magnetic properties of the itinerant ferromagnet LaCrGe3 under pressure studied by La139 NMR

“…Quite recently, the detailed studies on LaCrGe 3 using thermodynamic, transport, x-ray, neutron scattering and μSR measurements reported a modified zero-field phase diagram [T -p phase diagram, see Fig. 1(b)] [28]. Similar to the previous report [25], a clear tricritical point has been reported with FIG.…”

“…The high-pressure magnetic (HP-MAG) state is represented by the yellow colored area. It is noted that the HP-MAG state was initially considered as an antiferromagnetic state [25], but the recent measurements suggest a short-range ferromagnetic ordered phase as shown in (b) [28]. (b) Recent T -p phase diagram in zero magnetic field for LaCrGe 3 after Ref.…”

“…(b) Recent T -p phase diagram in zero magnetic field for LaCrGe 3 after Ref. [28]. The blue-shaded region corresponds to the region of FM order, which is schematically depicted in the insets by spins (arrows) pointing along the c axis.…”

“…a slightly different position [p = 1.5(1) GPa, T = 53(3) K]. According to Gati et al [28], the phase appearing under high p is likely not an AFM state but a form of disordered shortrange FM clusters. These results suggest that the avoided FM criticality in LaCrGe 3 has two features: (1) the change in the transition character from second order to first order and (2) the appearance of short-range ferromagnetic order rather than AFM order.…”

Field-Induced Modulated State in the Ferromagnet PrPtAl

“…For excess Fe (y ≳ 0.004), the modulated state is undercut by FM at low temperature, giving a behavior resembling that in PrPtAl. An avoided QCP under pressure in LaCrGe 3 [14,15] has recently been shown to give way to short-range order, rather than long-range modulated antiferromagnetism [16].…”