Tricritical wings and modulated magnetic phases in LaCrGe3 under pressure

Abstract

Experimental and theoretical investigations on itinerant ferromagnetic systems under pressure have shown that ferromagnetic quantum criticality is avoided either by a change of the transition order, becoming of the first order at a tricritical point, or by the appearance of modulated magnetic phases. In the first case, the application of a magnetic field reveals a wing-structure phase diagram as seen in itinerant ferromagnets such as ZrZn2 and UGe2. In the second case, no tricritical wings have been observed so far. Here, we report on the discovery of wing-structure as well as the appearance of modulated magnetic phases in the temperature-pressure-magnetic field phase diagram of LaCrGe3. Our investigation of LaCrGe3 reveals a double-wing structure indicating strong similarities with ZrZn2 and UGe2. But, unlike these simpler systems, LaCrGe3 also shows modulated magnetic phases similar to CeRuPO. This finding provides an example of an additional possibility for the phase diagram of metallic quantum ferromagnets.

Ferromagnetic quantum criticality: New aspects from the phase diagram of LaCrGe3

“…Interestingly, there are two successive transitions, as in the case of UGe 2 [32]. Another related similarity with UGe 2 is a broad anomaly in the temperature dependence of resistivity at low pressures within the FM state [10]. This indicates that, similar to UGe 2 , LaCrGe 3 has two ferromagnetic states (FM1 and FM2) which differ in magnetization value.…”

“…It vanishes around 40 K which corresponds to the temperature of the so-called tricritical point: the point at which the transition changes between first and second order. The stronger evidence for a first order transition comes from the observation of metamagnetic transitions for temperature below and pressure above the tricritical point when the field is applied along the easy axis of magnetization (c-axis) [10]. Indeed, this is a direct consequence of the transition being of the first order: as a first order ferromagnetic transition is suppressed, an applied magnetic field is able to re-induce the transition.…”

“…In UGe 2 and LaCrGe 3 , the tricritical point is near 24 and 40 K, respectively. During our recent investigation of the wing structure phase diagram of LaCrGe 3 , a careful determination of the wing near the tricritical point revealed a near tangent merging of the transition lines [10]. In fact, simple considerations using Landau theory of phase transitions revealed that the tangent merging of the wing lines at the tricritical point is general and should be observed in the other materials as well [41].…”

“…5, the hysteresis behavior of the metamagnetic transitions disappears at a critical point as the temperature is increased. The lines of critical points form a wing-structure phase diagram in the T -p-H space which has been determined recently in LaCrGe 3 [10], and is shown in Fig. 6.…”

“…In the same way as pressure can initially decrease the freezing point of water, physicist have been able to use pressure to decrease the Curie temperature to absolute zero temperature, leading to a quantum phase transition. Surprisingly, a variety of unconventional properties have been unveiled near the ferromagnetic quantum phase transition [1], including superconductivity [2][3][4][5], non-Fermi liquid behavior [6], tri-criticality [5,[7][8][9][10], and complex magnetic structures [11][12][13][14][15][16].…”