Spin-glass–like ground state and observation of exchange bias in Mn _0.8 Fe _0.2 NiGe alloy

Abstract

The ground-state magnetic properties of a hexagonal equiatomic alloy of nominal composition Mn0.8Fe0.2NiGe were investigated through dc magnetization and heat capacity measurements. The alloy undergoes a first-order martensitic transition below 140 K with simultaneous development of long-range ferromagnetic ordering from the high-temperature paramagnetic phase. The undoped compound MnNiGe has an antiferromagnetic ground state and it shows martensitic-like structural instability well above room temperature. Fe doping at the Mn site not only brings down the martensitic transition temperature, but it also induces ferromagnetism in the sample. Our study brings out two important aspects regarding the sample, namley i) the observation of exchange bias at low temperature, and ii) spin-glass–like ground state which prevails below the martensitic and magnetic transition points. In addition to the observed usual relaxation behavior, the spin glass state is confirmed by the zero-field–cooled memory experiment, thereby indicating cooperative freezing of spin and/or spin clusters rather than uncorrelated dynamics of superparamagnetic-like spin clusters. We believe that doping disorder can give rise to some islands of antiferromagnetic clusters in the otherwise ferromagnetic background which can produce interfacial frustration and exchange pinning responsible for spin glass and exchange bias effect. A comparison is made with doped rare-earth manganites where a similar phase separation can lead to a glassy ground state.

Hydrostatic pressure tuned magneto-structural transition and occurrence of pressure induced exchange bias effect in Mn0.85Fe0.15NiGe alloy

“…4 EBE is defined as the shift in the center of the M (H) isotherm while cooled in presence of external H. 4,22,23 EBE is particularly important because of its application in various technological fields, such as permanent magnets, magnetic recording media, sensors, and read heads.…”

“…and their derivatives have attracted renewed attentions for the observation of fascinating magneto-functional and physical properties such as, large magneticaloric effect (MCE), exchange bias effect (EBE), spin glass (SG) like ground state etc. [1][2][3][4][5][6][7][8][9][10][11][12] Among various members of MEAs, MnNiGe is one of the potential candidates which undergoes a first-order diffusionless structural phase transition, known as martensitic phase transition (MPT), at 470 K during cooling and orders spiral antiferromagnetically below 346 K. 1,3,4,8 Physical and chemical pressures are the two most influencing parameters that can affect the physical properties of these materials simply by modifying structural parameters like lattice volume, bond angle etc. 8,13,14 Among these two, chemical pressure approach (different doping studies) is much popular among the researchers due to easy sample preparation and measurement options.…”

“…FM strength again starts to decrease with further increase in Fe concentration and a SG like ground state was observed. 4,8 The direct exchange nature of the Mn-Mn intra-layer interaction plays the pivotal role towards the observation of non-monotonic effect of Fe-doping. In the present work, our aim is to address the effect of clean perturbation by applying external hydrostatic pressure on the structural and magnetic transition of a Fe-doped MnNiGe alloy with nominal composition Mn 0.85 Fe 0.15 NiGe.…”

Multifunctional behavior of Fe-doped MnNiGe magnetic equiatomic compound

“…Recently, magnetic equiatomic alloys (MEAs) of general formula MM X ′ (M, M transition ′ = metals, X ¼Si, Ge, Sn) have attracted renewed interest due to the observation of various magneto-functional properties, such as magnetic shape memory effect, exchange bias and large magnetocaloric effect [8][9][10][11][12][13]. The first-order diffusionless structural phase transition, called the martensitic phase transition (MPT), is the key to this functional behavior.…”

“…Recent studies indicate that Fe doping in Mn or Ni site induces ferromagnetism in otherwise antiferromagnetic alloy [11,16]. It has been found that Fe doping in tandem with the first order structural phase transition can give rise to coexisting fractions of ferromagnetic and antiferromagnetic phases and allows the samples to have large tenability under an applied magnetic field.…”