Pressure driven magnetic order in Sr[Formula: see text] Ca[Formula: see text] Co[Formula: see text] P[Formula: see text]

The magnetic phase diagram of Sr[Formula: see text] Ca[Formula: see text] Co[Formula: see text] P[Formula: see text] as a function of hydrostatic pressure and temperature is investigated by means of high pressure muon spin rotation, relaxation and resonance ([Formula: see text] SR). The weak pressure dependence for the [Formula: see text] compounds suggests that the rich phase diagram of Sr[Formula: see text] Ca[Formula: see text] Co[Formula: see text] P[Formula: see text] as a function of x at ambient pressure may not solely be attributed to chemical pressure effects. The [Formula: see text] compound on the other hand reveals a high pressure dependence, where the long range magnetic order is fully suppressed at [Formula: see text] kbar, which seem to be a first order transition. In addition, an intermediate phase consisting of magnetic domains is formed above [Formula: see text] kbar where they co-exist with a magnetically disordered state. These domains are likely to be ferromagnetic islands (FMI) and consist of an high- (FMI-[Formula: see text] ) and low-temperature (FMI-[Formula: see text] ) region, respectively, separated by a phase boundary at [Formula: see text] K. This kind of co-existence is unusual and is originating from a coupling between lattice and magnetic degrees of freedoms.